Module 6
Water, Vitamins, Minerals, Diet Planning and Supplements
A. Water Loss, Intake, Balance, and Imbalance
Water is often considered the most important nutrient. Failure to consume
other nutrients may result in harmful deficiencies Over a span of weeks, months, or
years, but humans can live for only a few days without water. It is the most abundant
substance in the body, compnising approximately 60 percent of an average person's
body weight. Water provides the aqueous medium for chemical reactions and other
processes within cells, transports substances throughout the body, facilitates
thermoregulation (maintenance of body temperature), and is critical to most other
physiological processes. Because of the additional physiological stress generated by
physical activity, exercise, and sport, fluid balance is an important consideration for
athletes and active people.
There are two major aspects to fluid balance that must be considered and
understood: (1) water volume and (2) the concentration of solutes in body fluid. First,
the body must have an adequate volume of water to meet physiological demands, a
condition referred to as euhydration. An excess amount of water is generally a
temporary condition in healthy people and is called hyperhydration, whereas an
insufficient volume of water in the body is termed hypohydration. The term
dehydration refers to the process of losing body water and moving from a state of
euhydration to hypohydration. Dehydration is often used interchangeably with
hypohydration, but these terms have different meanings.
Second, because of the potential for water to move from one area to another
by osmosis due to concentration differences, the overall concentration of substances
dissolved in body water must be considered as well. This is the concept of tonicity;
body fluids are considered to be hypotonic, isotonic, or hypertonic if they have a
concentration of solutes that is less than, the same as, or greater than the concentration
of solutes in the cells respectively. Although a number of substances are osmotically
active, the tonicity of body fluids is due largely to the concentration of electrolytes,
electrically charged cations such as sodium (Na*) and potassium (K*), and anions
such as chloride (Cl-) and phosphate (PO,*>).
The amount of water in the body depends on a variety of factors, including
body size, gender, age, and body composition. In general, larger people have more
body water compared to those of smaller stature, and males have more water than
females because men typically have more muscle mass and less body fat than women.
Body water percentage has an inverse relationship with both age and body fatness; it
declines with advancing age and increasing body fatness. On average, an adult's body
is approximately 60 percent water by weight, but individuals may range from 40 to 80
percent. An average 70 kg (154 lb) male has approximately 42 liters (L) of total body
water, and the average female approximately 30 L. Expressed as a nonmetric
measurement, the average female and male have approximately 8 and 11 gallons of
body water, respectively.
Water is distributed throughout the body. This distribution is often separated
into two major compartments: intracellular fluid (ICF) and extracellular fluid (ECF).
Intracellular fluid consists of all the water contained within the trillions of cells in the
body. Some cells have higher concentrations of water than others. All of these cells
maintain their integrity because of their cell membranes, which separates the fluid
inside the cells from the extracellular fluid. The ECF is further divided into
subcompartments. One subcompartment is the plasma, the watery portion of the
blood. Another is the interstitial fluid, the fluid that is found between the cells.
Approximately two-thirds of total body water is in the ICF, leaving approximately
one-third in the ECF.
Osmotic pressure is measured in milliosmoles (mOsm). When the number of
particles (solute) is measured per kilogram of solvent, the correct term is osmolality;
when measured per liter of solvent, the correct term is osmolarity. In nutrition and
medicine, osmolarity is the standard term, whereas in exercise physiology the term
osmolality is more commonly used because osmolality is not affected by temperature.
In humans, there is little difference between the values when the two methods are
calculated and compared (Gropper, Smith, and Groff, 2009). In this textbook, the term
osmolarity will be used.
It is important to note that although the ionic composition differs between the
ICF and the ECF, the osmolarity or total concentration of all solutes in those
compartments is generally the same. Shifts in fluid between the ECF and ICF occur
solely due to osmosis, the movement of water from an area of lower concentration to
an area of higher concentration. Under normal homeostatic conditions, the
osmolarities of the ECF and ICF are the same, and there is no net movement of water.
However, if the concentration in either compartment changes, a fluid shift may occur.
If sodium increases in concentration in the extracellular fluid, water would move by
osmosis out of the cells and into the ECF in an attempt to dilute the extracellular fluid
and restore balance. For example, heavy sweating can cause a large loss of plasma
volume due to water loss, resulting in an increased concentration of sodium in the
plasma. This stimulates movement of water out of the cells (that is, ICF) and into the
plasma (that is, ECF), causing the cells to shrink. Conversely, if the concentration of
sodium in the extracellular fluid is decreased, the osmolarity of the ECF would be less
than that in the cells, and water would move by osmosis into the cells in an attempt to
correct the concentration imbalance. The resulting movement of water into the cells
would cause the cells to expand.
Water loss from the body is generally categorized as either insensible or
sensible. Insensible refers to avenues of loss that are not normally noticed by the
individual, including water lost through ventilation and through nonsweat diffusion
through the skin. With each breath, the inspired (inhaled) air is humidified to protect
delicate lung tissues from drying. The water vapor that is added is then lost with the
subsequent expiration, because the water is not recaptured before the air is exhaled
from the body. This water loss is typically not noticed except on cold days when we
can “see our breath.” When warm, humid air from the lungs is rapidly cooled by the
cold air outside, water vapor condenses into water droplets that can be readily seen.
Water losses by this route can increase in environments in which the air is colder and
drier, as more water vapor needs to be added to the inspired air. Increased levels of
ventilation as a result of exercise may also cause an increased insensible loss of water.
The renal system provides the major physiological mechanism for controlling
fluid balance in the body via the production and excretion of urine. Urine output can
vary dramatically, but for the average person under homeostatic conditions it is
approximately 1,500 ml per day (~54 oz or 6-7 cups). The amount of renal water loss
is highly variable and can be influenced by the amount of fluid and salt intake, renal
function, the action of various hormones, and the consumption of compounds that
have a diuretic effect.
The addition of water to the body is primarily accomplished through the fluid
content of beverages and foods consumed each day, and secondarily through
metabolism (Figure 7.6). On average, an adult will take in approximately 2,350 ml
(~84 oz or 10.5 cups) of water each day from beverage and food sources, but there
can be considerable variation depending on how much an individual eats and drinks.
Adults in the United States consume ~20-25 percent of their total daily water intake
via food, 35-40 percent from tap or bottled water, and the remainder from other
beverages.
The amount of water in the body is constantly changing, with fluid being
added and removed through the mechanisms discussed above. The body is said to be
in fluid balance if a sufficient amount of fluid is present that allows for the body to
function normally. Although the body has sensitive mechanisms to maintain fluid
balance over time, it is possible to exceed the capabilities of these mechanisms in
either the short or long term. In general, the amount of fluid consumed is not carefully
matched to the body’s daily needs. The usual overall strategy is to drink an excess of
water, retain what is needed to maintain fluid balance, and excrete the excess.
Deviations from this basic strategy can result in imbalances.
Consumption of large amounts of water very quickly (for example, 3,000 ml
or ~104 oz or ~13 cups in 4 hours, as some slow marathon runners have done) can
result in a state of hyperhydration that can actu- ally be dangerous to one’s health, and
can even result in death (Almond et al., 2005). The excess water dilutes the
concentration of solutes in the extracellular fluid. Before the kidneys have a chance to
excrete the extra water, the reduced osmolarity in the ECF provokes a shift of water
from the ECF into the cells, causing them to swell. Nerve cells, especially those in the
brain, are particularly sensitive to this swelling and may cease to function properly,
resulting in impaired brain function, coma, or even death. This condition can occur
during certain types of endurance exercise and is discussed later in this chapter (see
section on hyponatremia).
Distribution of water throughout the body is regulated by both the volume of
water and the osmolarity of the extracellular fluid. Osmolarity is influenced by the
concentration of solutes, particularly certain electrolytes. Sodium is the most
important electrolyte in the extracellular fluid because it exists in the largest amount
and therefore has a large and direct affect on osmolarity. The body must respond to
changes in the amount of sodium in the ECF by adjusting water volume. An increase
in sodium in the ECF will increase the volume of water and a decrease in sodium will
result in a decrease in ECF water volume. Other electrolytes that may influence water
distribution are potassium, calcium, magnesium, chloride, and phosphate.
The only route of intake for sodium is by ingestion, through either foods,
fluids, or rarely, salt tablets (sodium chloride). Similar to water, sodium is generally
consumed in excess of the body’s requirements and the body relies on the renal
system to excrete what is not needed. Many factors influence the amount of sodium in
the diet, but the largest factor in industrialized countries is the consumption of
processed foods at home and at restaurants. For the average American adult,
processed food is the source of 77 percent of daily sodium intake. The addition of
table salt (that is, sodium chloride) to foods accounts for approximately 11 percent of
daily sodium intake. The remaining sodium (~12 percent) occurs naturally in water
and in foods such as milk, vegetables, and grains.
Potassium, the pri- mary intracellular cation, is consumed via foods and
beverages or occasionally, through the use of a salt substitute (potassium chloride).
Potassium is abun- dant is unprocessed foods such as fruits, vegetables, whole grains,
beans, and milk. Low dietary potassium intake in the United States is a reflection of a
low daily fruit and vegetable intake and the high intake of pro- cessed foods;
processing results in substantial potas- sium losses. Examples of foods with a high
potassium content include bananas, orange juice, and avocadoes. Less than 3 percent
of U.S. adults are likely to receive an adequate amount of potassium from their diets
(Institute of Medicine, 2004). Potassium found in food is easily absorbed from the
gastrointestinal tract (greater than 90 percent absorption).
Although there are several electrolytes involved in fluid and electrolyte
balance, the initial dietary focus tends to be on sodium and potassium. Two other
cations—calcium and magnesium— are discussed in Chapter 9. The corresponding
anions, such as chloride and phosphate, receive little dietary attention. The chloride
content of the diet can be reasonably well predicted from salt intake and phosphorus is
widely found in food. A dietary deficiency of either would be extremely rare.
B. Effect of Exercise on Fluid Balance
Under normal conditions, most healthy sedentary individuals regulate their
fluid balance (that is, achieve homeostasis) relatively easily. Thirst and hunger
mechanisms usually lead people to consume water in excess of the body’s daily needs,
with the excess being excreted. If there is a shortfall in fluid consumption, the body
can respond in the short-term by reducing urine excretion, which conserves water and
maintains fluid balance. Exercise challenges fluid homeostasis because of the critical
role that body fluids play in thermoregulation (maintaining an appropriate body
temperature). Exercise causes an increase in body temperature, and a major
mechanism for lowering body temperature is the evaporation of sweat. The loss of
fluid through sweat may have a large impact on fluid balance, in both the short and
long term. Physical activity or exercise, especially in hot and humid conditions,
represents a substantial challenge for the regulation of body temperature, fluid
homeostasis, and, subsequently, performance (Armstrong and Epstein, 1999). In
contrast to sedentary individuals who can regulate their fluid balance easily, athletes
may have a difficult time preventing dehydration and severe hypohydration. These
conditions can negatively impact training, performance, and health.
Exercise can result in water shifting between compartments within the body
and in accelerated loss of water from the body. As the cardiovascular system adjusts
to the demands of exercise by increasing blood flow and oxygen delivery, the
increased pressure in the blood vessels results in some of the fluid leaking into the
surrounding interstitial space. This fluid is lost from the plasma and plasma volume
therefore declines slightly as the water shifts within the extracellular fluid
compartments. This decrease in plasma volume occurs within the first few minutes
after exercise begins with the amount being largely dependent upon the exercise
intensity. The decline may be up to approximately 5 percent of plasma volume if the
exercise is intense. As explained earlier, an average adult male has approximately 2.8
L of plasma. A5 percent loss would be approximately 140 ml (5 oz) of water, an
amount that would not likely impair exercise performance. However, plasma volume
losses up to 10-20 percent can occur with prolonged exercise, and losses of this
magnitude may compromise cardiovascular function and ultimately reduce exercise
performance.
The rate at which the body loses water through sweating depends upon a
variety of factors. Exercise intensity can influence sweat rate through its independent
effect on core temperature. At any given room temperature, increased exercise
intensity results in higher body temperatures, and higher body temperatures will
stimulate higher sweat rates. Increased exercise intensity requires higher energy
expenditure, which results in a greater amount of metabolic energy being converted to
heat.
Clothing, uniforms, and protective gear may fur- ther influence the rate of
sweating by providing a bar- rier to heat loss. This type of clothing may provide an
insulating effect, trapping more heat in the body, or it may adversely affect the
evaporation of sweat by reducing the surface area of the skin that is exposed. Athletes
in sports with certain uniform traditions or requirements may be at greater risk for
heat injury and fluid imbalances. Football uniforms provide an excellent example.
They generally cover most of the skin and have thick padding in many places that can
have an insulating effect. Protective gear such as helmets, arm wrappings, padding,
and gloves add to the thermoregulatory challenge and may result in greater fluid loss
through sweat. Other examples include the fire protection gear worn by firefighters,
hazardous materials suits worn by public safety workers, and chemical warfare
protection suits worn by military personnel.
Consider a world-class female runner competing in the Olympic Marathon,
which is contested during the Summer Games, often in hot and humid conditions. She
will run for a little over 2 hours and could lose approximately 2 L of sweat per hour or
a total of 4 L of water! This may approach 10 percent of total body water or almost 10
pounds of water weight loss in a 100- pound runner if she were to consume no fluids.
With such a sweat rate, it is easy to see how large amounts of fluid can be lost very
quickly under certain exercise or environmental conditions. Because fluid
homeostasis is a balance of water intake and loss, fluid intake is essential. But can an
athlete prevent overall fluid loss when sweating heavily by drinking water or other
fluids?
Dehydration, or moving to a state of hypohydration as a result of fluid loss,
can have an adverse impact on core temperature and ultimately on exercise
performance (Sawka et al., 1998). When there is a loss of body water, the majority of
the water comes initially from the ECF, specifically from the plasma. Therefore, as
body water is lost through heavy sweating, there is a gradual loss of blood volume, a
condition known as hypovolemia. Because sweat is hypotonic in relation to blood,
fewer electrolytes and other solutes are lost in sweat in proportion to the amount of
water lost. In this case, the plasma that remains is more concentrated and its
osmolarity increases. Both of these conditions may adversely affect thermoregulation
and exercise performance.
The main function of blood flow is to deliver oxygen-laden blood to tissues,
and the need for oxygen delivery is greatly increased during exercise, particu- larly in
the exercising muscles. Blood flow also helps to control body temperature, and this
thermoregulatory function is used to a greater extent during exer- cise in the heat. A
finite and relatively small amount of blood is available to fulfill both these functions,
and exercise in the heat sets up a competition for this limited resource. The situation
gradually becomes worse as the athlete dehydrates because total blood volume
continues to decline.
Fluid loss through sweating is the major concern for the exercising athlete, but
sweat is composed of more than water. Sweat contains the electrolytes sodium,
potassium, and chloride; small amounts of minerals such as iron, calcium, and
magnesium; and trace amounts of urea, uric acid, ammonia, and lactate. Of these,
sodium is present in the largest amount. During light sweating, sodium and chloride
are reabsorbed from the tubule of the sweat gland and are not lost in large amounts.
During heavy sweating, however, the sweat moves through the tubule at a rate that is
too fast for substantial reabsorption, so sodium and chloride losses are proportionally
greater.
Athletes who train and eompete at these distances and durations should
experiment during training to determine the need for sodium and carbohydrate
replacement during exercise. For example, an athlete who is a heavy sodium excreter
can look for accumulation of salt on skin or clothing after training and experiment
with various replacement strategies during and after exercise (Maughan and Shirreffs,
2008). Although the focus of this chapter is water and electrolytes, the intensity and
length of time of activities such as marathon running and Olympic distance triathlons
also result in substantial utilization of carbohydrate stores, and the ingestion of
carbohydrates to maintain the availability and use of this fuel is also important.
Athletes may experience painful muscle cramps during or immediately after
exercise, known as exercise-associated muscle cramping (EAMC). It has long been
believed that such cramping is due to dehydration, changes in electrolyte
concentrations, or both. Therefore, athletes have been advised to hydrate properly and
eat more foods rich in potassium such as bananas. In addition, potassium, calcium,
and magnesium supplements are advertised to athletes as a way to prevent or recover
from muscle cramps. The ingestion of sodium via 1-2 oz (30-60 ml) of pickle juice
has also been recommended.
Despite a widespread belief that EAMC in all athletes is caused by
dehydration and electrolyte loss, the scientific evidence that supports this theory is
rather limited (Schwellnus, 2009). Although EAMC often occurs in conjunction with
heavy sweating, dehydration, and electrolyte losses, there is not strong evidence that
athletes who experience cramping have significantly different levels of dehydration or
electrolytes than noncramping athletes. Experimental intervention studies also do not
provide strong evidence for this approach. For example, limited studies of pickle juice
have failed to show its effectiveness in relieving EAMC (Miller et al., 2010; Miller,
Mack, and Knight, 2009). The American College of Sports Medicine (ACSM) (Sawka
et al., 2007) position paper notes that recommendations to avoid dehydration and
sodium deficits to prevent muscle cramps is based on consensus and usual practice
(that is, Evidence category C) not experimental evidence (that is, Evidence categories
A and B).
Some athletes experience exertional heat cramps, which is total-body
cramping when exercising in the heat. This type of cramping can involve muscles all
over the body, not just the ones directly involved in the exercise, and does appear to
be caused by sodium depletion and dehydration as well as muscle fatigue. Case
studies of tennis and football players suggest that exertional heat cramps may be the
result of rapid and large losses of fluid and sodium. Those who fall into this group,
known as “salty sweaters,” benefit from sodium-containing beverages during exercise
and the consumption of an adequate amount of sodium and water after exercise
(Bergeron, 2007). Adding salt to food, eating salty foods, and consuming beverages
with sodium are all ways to replenish sodium before the next exercise session. Salty
sweaters must closely match salt (sodium chloride) and fluid intake to sodium,
chloride, and fluid losses on a daily basis. As there are many nonnutritional causes of
cramping (for example, lack of stretching), each athlete should determine the likely
causes of their cramping and, through trial and error, institute strategies that are
known to prevent the causative factors.
C. Strategies to Replenish Water and Electrolytes
Exercise and physical activity can have a substantial impact on fluid balance.
Water and electrolyte loss must be compensated for to maintain long-term fluid
homeostasis. Single events or bouts of exercise may cause large disruptions in fluid
balance and need immediate attention. However, many athletes experience small
deficits on a daily basis, and these small cumulative deficits become more pronounced
deficits over several days or weeks. Athletes should develop a practical approach to
monitoring their hydration status and a strategy for water and electrolyte replacement
to maintain a status of euhydration and appropriate osmolarity.
There are a variety of ways to monitor the body's hydration status. These
methods have varying degrees of accuracy, difficulty, and expense. Typically, the
methods that are the most accurate are also the most difficult and time-consuming to
perform and the most expensive. These methods are best suited for use in research
studies and are rarely practical for day-today use by athletes or those who exercise or
compete recreationally. Daily monitoring requires an approach that is practical, and
easy to administer and understand.
To precisely determine an individual’s hydration status, the amount of total
body water and the osmolarity of the plasma must be known. Accurate measures of
total body water are often determined using isotope dilution, most commonly
deuterium oxide (also discussed in Chapter 2). When a known volume of water
having a known radioactivity level is consumed, it is diluted as it is absorbed and
distributed throughout the water compartments of the body. After distribution and
equilibration, a sample of body water can be taken and analyzed for its radioactivity.
Total body water volume can then be determined from the degree of dilution of
radioactivity. This method, though accurate, is expensive and time-consuming,
requires trained personnel, and is not suitable for daily monitoring.
One of the challenges for athletes and professionals who work with them is to
translate scientifically based recommendations into practice. Athletes have many
questions about water, sports beverages, and foods that may be used to replenish fluid,
electrolytes, and carbohydrates. No single strategy or product is “best” for all athletes;
each athlete needs a personalized plan. Development of an individualized plan
involves four steps: assessment, goals, actions, and reassessment.
Successful planning begins with assessment of hydration and electrolyte
status. For practical reasons, most athletes self-assess their hydration status by using
thirst, urine color, and/or body weight to roughly determine if they are adequately
hydrated. Self-assessment of electrolytes is more difficult and is often based on
observing salt crystals on skin or clothing, tasting salty sweat, or experiencing
conditions known to result in the loss of electrolytes such as vomiting or diarrhea.
Any athlete who has experienced electrolyte-related conditions, such as hyponatremia
or exertional heat cramps, should consult with medical professionals, such as a sports
medicine physician or a sports dietitian.
Athletes should be encouraged to consume enough fluid to match fluid loss
and prevent performanceattenuating hypohydration, while not exceeding the amount
of fluid lost. A substantial reduction in the incidence of hyponatremia in an
ultradistance triathlon was observed after participants were educated about
appropriate fluid intake, and access to fluids during the race was decreased slightly by
reducing the number of fluid stations and increasing the distance between them
(Speedy, Rogers, Noakes, Thompson, et al., 2000) Because the body’s fluid balance
mechanisms can be temporarily overwhelmed, an athlete’s fluid and sodium intake is
an important part of fluid homeostasis.
Dehydration can have an adverse effect on training and performance, thus
athletes have attempted to manipulate body fluid levels prior to exercise by
hyperhydrating. The idea is to increase the amount of body water prior to exercise so
when fluid is lost during exercise, a critical level of hypohydration is not reached as
quickly. Theoretically, this could prevent or delay a decline in performance. Short-
term hyperhydration can be achieved relatively easily by fluid overload, the
consumption of excess fluids in the hours before exercise. This overconsumption
results in an increase in total body water, an increase in plasma volume, and a
potential improvement in thermoregulation and exercise performance in the heat.
Because the kidneys react quickly to an overload of fluid, urine production is
increased and the resulting full bladder and need to urinate may be an interfering
factor for the upcoming exercise. Consumption of large quantities of fluid may also
result in gastric discomfort. Hyponatremia may also be a concern if very large
volumes of hypotonic fluid are consumed.
D. Classification of Vitamins
Vitamins are essential nutrients needed in small quantities for the proper
functioning of the body. Table 8.1 lists 13 vitamins that have been identified as
essential. Vitamins are often classified based on their solubility. Those vitamins that
are fat soluble include vitamins A, D, E, and K. All of the B vitamins (thiamin,
riboflavin, niacin, pantothenic acid, biotin, folate, B,, and B,,) and vitamin C are water
soluble. Some of the characteristics associated with vitamins are related to their
solubility.
The fat-soluble vitamins are absorbed and transported in the same way as fat
(see Chapter 6). Absorption may take several hours and transport in the blood requires
that they be bound to a carrier. Fat-soluble vitamins are stored in liver and adipose
(fat) cells. Although each fat-soluble vitamin has a recommended daily intake, the
ability to store these vitamins means that daily intake can vary without immediate risk
for deficiency. For example, on days when vitamin E intake is lower than usual, the
body has a ready store of vitamin E for use. On days when vitamin E intake is
adequate, stores that have been reduced can be increased. This ability to store fat-
soluble vitamins helps the body to guard against deficiencies, but it also means that
toxicities can occur if excessive amounts are consumed over long periods of time.
These toxicities, although rare, can cause substantial health problems, especially in a
major organ such as the liver. Optimal intake—not too little, not too much—is an
important goal.
Vitamins play an important role in overall health. Because each vitamin plays
a specific role that cannot be replaced or substituted by another vitamin, it is
important to consume an adequate amount of each vitamin. Consumption of excessive
amounts of vitamins should be avoided since toxicities, even of certain water-soluble
vitamins, can occur. Two sets of guidelines have been created that help quantify
adequate but not excessive amounts. As discussed in Chapter 1, the Dietary Reference
Intakes is a set of values that helps answer the question, “How much [of a nutrient] is
needed each day?” The Tolerable Upper Intake Levels (UL) help address the question,
“How much is too much?”
There are a number of ways in which exercise could alter vitamin
requirements. These include (1) decreased absorption from the gastrointestinal tract,
(2) increased loss via sweat or urine, (3) increased utilization due to the stress of
exercise, or (4) increased need associated with large gains and maintenance of skeletal
muscle mass. Alternatively, there are a number of adaptations the body can make to
the stress of exercise that might preserve vitamins. For example, exercise may cause
the body to decrease excretion or effectively recycle vitamins. Because the body has
so many adaptive mechanisms in response to exercise, an increase in utilization does
not necessarily mean an increase in dietary need.
At the present time the effect that exercise has on vita- min requirements is
presumed to be relatively small, and any small additional demand is adequately cov-
ered by the requirements set forth for sedentary humans. Perhaps the most striking
feature that stands out in a review of the scientific literature in this area is not
evidence of an increased demand for vitamins imposed by the stress of exercise, but
the marginal dietary intake of vitamins that exists for some athletes as well as by
sedentary adults.
Vitamin deficiencies do not occur overnight, especially in previously well-
nourished adults. Any vitamin deficiencies will progress through stages—at first mild,
then moderate, and ultimately, severe. Severe deficiencies are termed clinical
deficiencies whereas mild and moderate deficiencies are called subclinical
deficiencies. These terms describe indistinct points on a continuum. There are no
clear-cut divisions between mild and moderate and moderate and severe deficiencies.
Mild deficiencies can develop if vitamin intake is poor or absent. As discussed
previously, many adult diets are lacking sufficient amounts of vitamins and, over time,
mild vitamin deficiencies can develop. In a few cases the intake of a vitamin could be
zero. For example, vegans do not consume any animal-derived products and their
diets could be devoid of vitamin B,,, which is found only in animal foods. Vitamins
must also be properly absorbed and utilized by the body, which is the case for most
people, but poor vitamin absorption can be a consequence of some gastrointestinal
diseases. Inadequate vitamin intake from the diet is one of the few factors associated
with vitamin deficiencies that can be easily documented. The first step in determining
a potential vitamin deficiency is an assessment of usual vitamin intake from food.
E. The Roles of Vitamins in the Body
Each vitamin has a unique chemical composition as well as specific
biochemical roles. Many vitamins are involved with enzymatic activity, particularly as
part of a coenzyme. Enzymes are proteins that regulate metabolic reactions. Some
enzymes depend solely on their protein structure to function, but many require a
cofactor, which helps the enzyme to be more stable. The cofactor may be a vitamin or
a mineral ion. When the enzyme contains a cofactor it is referred to as a coenzyme.
Coenzymes are usually involved in speeding up a reaction, typically by transferring a
functional group as substrates are converted to other compounds.
Thiamin (B,), riboflavin (B,), niacin (B,), vitamin B,, pantothenic acid, and
biotin are often referred to as the B-complex vitamins. These vitamins are primarily
involved in the production of ATP as they are part of the enzymes that regulate these
reactions. Table 8.4 lists some of the vitamins and their associated coenzymes and
biochemical pathways, whereas Figure 8.3 highlights the vitamin-containing
compounds involved in energy metabolism.
Athletes in training produce more ATP than nonathletes, so another logical
question is whether athletes need more thiamin than sedentary individuals. Although
the number of studies is limited, it does not appear that exercise increases the need for
thiamin. Dietary intake studies have found that most athletes consume a sufficient
amount of thiamin. When energy expenditure is high, many athletes focus on
consuming high-quality carbohydrates, such as breads, cereals, and grains, to ensure
that muscle glycogen is adequately resynthesized. In doing so, they consume
sufficient thiamin and meet or exceed the DRI for this vitamin. Low thiamin intake in
athletes is typically associated with caloric restriction and consumption of low-
nutrient-dense carbohydrates, such as foods or beverages high in sugar and low in
fiber and vitamins
Riboflavin is part of two coenzymes involved in ATP production, flavin
mononucleotide (FMN) and flavin adenine dinucleotide (FAD). These coenzymes are
necessary for the numerous oxidationreduction reactions that occur because they can
accept or release hydrogen atoms (Figure 8.3). The synthesis of these enzymes is
under hormonal control. When tissues are saturated with riboflavin the excess is
excreted in the urine. Exercise increases the need for riboflavin (Woolf and Manore,
2006). Most athletes consume sufficient riboflavin, although there have been reports
of low intake by athletes who consume too few kilocalories. Riboflavin is found in a
wide variety of foods such as breads and cereals, vegetables, meat, and dairy products
such as milk, and athletes consuming a sufficient amount of energy would not likely
be deficient.
Many people are somewhat familiar with thiamin, riboflavin, niacin, and
vitamin B, but may be unfamiliar with the remaining B-complex vitamins,
pantothenic acid and biotin. Although these vitamins may be mentioned less often,
they are almost always included in vitamin B-complex supplements. Pantothenic acid
is part of coenzyme A (CoA), an important compound in aerobic metabolism. Like
other enzymes, acetyl CoA is made up of two parts, acetate (also known as acetic
acid) and coenzyme A. Pantothenic acid is intimately involved in energy metabolism
as a part of this compound, but large amounts of pantothenic acid do not increase the
rate of energy reactions. Biotin is also involved in a number of energy-related
reactions.
Oxygen is needed to produce ATP from carbohydrates, fats, or proteins by our
aerobic energy pathways, that is, oxidative phosphorylation. The majority of oxygen
used in oxidative phosphorylation reactions is reduced to water but a small percentage
(~4—-5 percent) is not. Instead, free radicals are produced. Free radical is a broad
term that includes reactive oxygen species (ROS), such as ozone and superoxide
radicals, and reactive nitrogen species (RNS), such as nitric oxide. Free radicals are
unstable chemical compounds that can destroy cells by damaging cellular membranes,
proteins, and DNA. These compounds will always be present because they are part of
normal physiological processes, including exercise. In fact, some free radicals help to
destroy bacteria and other foreign particles, so they can have beneficial effects.
However, in excessive amounts free radicals have many detrimental effects and the
body has several mechanisms to counteract them. The key issue is that there is a
balance between rate of production and rate of clearance. When the balance favors the
overproduction of free radicals then oxidative stress occurs, which can lead to
damaged cells, tissues, and organs.
One of the more intriguing aspects of this type of research is the reported
increase in oxidative stress in some athletes who use antioxidant supplements.
Scientists have been trying to determine why antioxidant supplements might produce
detrimental effects. One theory is that antioxidant vitamins in high concentrations act
as pro-oxidants. Pro-oxidants increase the formation of free radicals and enhance
oxidative damage. In the case of vitamin C, pro-oxidant activity can occur at high
concentrations but the effect is indirect since the vitamin C reacts with copper and
iron, which then interact with other compounds to form free radicals. The
concentration of vitamin C in the blood is one of at least three factors that determines
if the vitamin C acts as a pro-oxidant or an antioxidant.
Vitamin E is the primary antioxidant found on or near cell membranes. Cell
membranes contain a high proportion of polyunsaturated fatty acids, which can be
oxidized by a variety of free radicals. The destruction of the lipid in the cell
membrane is a chain reaction requiring several steps. Vitamin E’s role is to break the
chain reaction. Free radicals are a thousand times more likely to react with vitamin E
than with polyunsaturated fatty acids (Viitala et al., 2004). For these reasons, vitamin
E is an essential vitamin because it can prevent oxidative damage and maintain the
integrity of cell membranes. Severe damage to cell membranes would cause the cell to
leak fluid, leading to cellular death. As noted earlier, once vitamin E acts as an
antioxidant it must be regenerated. Several compounds can regenerate vitamin E
including vitamin C. The ratio of vitamin E to unsaturated fatty acids in cell
membranes is estimated at 9:1,000- 2,000. Therefore, a very important part of the
body’s defense mechanisms is the regeneration of vitamin E.
Vitamin A is a broad term and includes both preformed vitamin A (for
example, retinol) and vitamin A precursors, known as carote- noids. Carotenoids,
which are found in the red, orange, and yellow pigments in plants, have some
antioxidant properties. Beta-carotene is the best known and most studied carotenoid
but it is a less powerful antioxidant than some of the other carotenoids, such as
lycopene and lutein. Compared to vitamin E, carotenoids are weak antioxidants.
However, they do interact with some reactive oxygen species (for example, singlet
oxygen molecules) and inactivate them. Due to their chemical properties, the
carotenoids do not need to be regenerated, as is the case for vitamin E and C.
Vitamins A and D are associated with growth and development in various
ways. Although both are fat soluble, these two vitamins have very different chemical
structures. Vitamin D has four rings, one of which is broken. This structure allows it
to easily bind with proteins. The basic structure of vitamin A is a ring and a
polyunsaturated side chain, but because the side chain can be different there are a
number of closely related compounds that have vitamin A activity. These compounds
can interact with or be converted to other compounds, so vitamin A has many
different functions in the body.
Vitamin A toxicity is rare, but it can occur. The UL is 3,000 mcg of preformed
vitamin A. Excess preformed vitamin A can cause liver damage. Vitamin A toxicity is
associated with birth defects, so pregnant women are cautioned to supplement with a
safe dose of vitamin A as prescribed by their physician. Vitamin A toxicity from beta-
carotene is highly unlikely because of its relatively low rate of absorption and the
amount that can be converted to preformed vitamin A is well regulated by the body.
F. Sources of Vitamins
Most vitamins are obtained from three sources: they exist naturally in food,
they are added to foods during processing, and they are manufactured as dietary
supplements. An orange is a food that naturally contains approximately 70 mg of
vitamin C. A fruit punch drink with vitamin C added has about 50 mg. Vitamin C
supplements come in 100, 300, 500, and 1,000 mg tablets. The vitamin C found in
each is the same chemical compound but the dose can vary considerably.
Athletes, like other consumers, have many questions about vitamins. Can
athletes meet their daily vitamin needs by eating food alone? Are there advantages to
getting vitamins from food instead of from supplements? Are there advantages to
using vitamin supplements? Will taking a multivitamin every day do the trick? As is
often the case in a complicated subject like nutrition, many factors must be considered
before such questions can be answered.
Are there advantages to getting vitamins from food? The answer is yes.
Vitamins are found naturally in food with water, minerals, and other biologically
active compounds and they provide needed calories in the form of carbohydrate,
protein, and/or fat. In other words, when you get vitamin-rich foods you get more than
just the vitamins. Vitamin supplements are singular in focus—they provide only
vitamins. As mentioned previously, vitamins are required for energy metabolism but
they do not provide energy-containing compounds—carbohydrates, proteins, or fats.
In a previous section, the answer to the question “Can eating food alone meet
the daily vitamin needs of an athlete?” was yes. But each athlete must ask another
question, “Does my diet provide the vitamins I need?” The answer to that question
depends on the amount and types of foods consumed. One way to estimate the
nutrient content of one’s diet is to record food intake for 3 to 7 days by using a food
diary (see Appendix E). All foods and beverages consumed can then be entered into a
computer program that estimates the nutrient content of the diet and compares it to the
DRI. In the case of vitamins, estimated intake can also be compared to the Tolerable
Upper Intake Levels.
Adding vitamins to food began in the United States as a way to prevent
vitamin deficiencies, which were widespread in the 1930s and 1940s. In the 2000s,
manufacturers began adding vitamins to foods such as meal replacement bars, energy
bars, and energy beverages, products that are highly marketed to athletes. To gain
market share in the highly competitive new product market, manufacturers are adding
“nutrient horsepower” to foods. In other words, they are adding many vitamins in
high doses so consumers perceive their products as being more nutritious than other
similar products.
It behooves athletes to look carefully at the dose of any multivitamin
supplement that they are considering taking. The amounts shown in Table 8.13 and
Table 8.14 are from actual supplements available for purchase. Table 8.13 is typical of
the amounts shown in a one-a-day type multivitamin supplement, whereas Table 8.14
is typical of a high-potency vitamin supplement. The UL is provided as a basis of
comparison but is not required to appear on the supplement label. Notice that the
amounts contained in the high-potency vitamin supplement are very high when
compared to the Daily Value. Despite the high levels, such vitamin preparations are
legal to sell.
G. Classification of Minerals
Vitamins and minerals are often mentioned in the same breath. Although there
are some similarities between these classes of nutrients, minerals differ from vitamins,
especially watersoluble vitamins, in several ways. The chemistry, absorption,
metabolism, and excretion of minerals are generally very different when compared to
vitamins. In the case of two minerals, calcium and iron, there are medical tests that
can help quantify the amount in the body, providing valuable information for
detecting and treating low bone density and iron deficiency.
Twenty-one minerals have been identified as essential as shown in Table 9.1.
Minerals are often divided into two categories based on the amount found in the body.
Those found in relatively large amounts (about 5 g in a 60 kg [132 lb] person) are
termed macrominerals and include calcium, phosphorous, magnesium, sodium,
potassium, chloride, and sulfur. Microminerals, also known as trace minerals, are
found in comparatively smaller amounts in the body. These include well-known
minerals, such as iron, as well as lesser-known ones, such as manganese and
molybdenum.
Another classification method for minerals is based on function. Minerals
critical to proper bone formation include calcium, phosphorus, magnesium, and
fluoride. Several minerals are electrolytes and have either a positive or negative
charge. Sodium, potassium, and chloride are prime examples of minerals that function
as electrolytes and help to maintain body fluid balance. Iron is central to proper red
blood cell formation. Many enzymes contain minerals such as zinc, selenium, or
copper, and some of these minerals are necessary for the proper functioning of the
immune system.
Minerals may also be lost in urine. For example, acute exercise results in
increased postexercise zinc blood concentration, as zinc moves from muscle cells into
the extracellular fluid. Some of this zinc may then be excreted via the urine. Similarly,
more iron may be lost in the urine of athletes than in sedentary individuals (Gleeson,
Nieman, and Pedersen, 2004; Gleeson, Lancaster, and Bishop, 2001). Although it is
recognized that mineral loss can be greater in athletes, it is also known that the
consumption of excess miner- als, such as zinc and iron, can be detrimental to the
athlete by compromising the immune system (Gleeson, Nieman, and Pedersen, 2004).
Therefore, thought must be given to the best way to compensate for larger- than-
normal losses due to exercise. Moderate losses of minerals via sweat or urine can be
offset by adequate mineral intake from food. Athletes who have substantial losses
may need to increase their dietary intake or supplement the diet with the lost
mineral(s). The best approach should be determined on an individual basis.
It is difficult to draw broad conclusions about mineral intake by athletes
because individual intake can differ substantially among teammates in the same sport.
In general, athletes with a low energy intake are likely to be deficient in one or more
of the following minerals: calcium, iron, zinc, selenium, magnesium, and copper.
Energy-restricted athletes known to be at risk include distance runners, female
gymnasts, ballet dancers, teenage synchronized skaters, wrestlers, and jockeys. Some
studies have shown substantial deficits, particularly of iron and zinc. Some of the
trace minerals have not been assessed, but it is likely that athletes who are deficient in
iron and zinc are also deficient in some of the other trace minerals. These athletes are
also likely to have low vitamin intakes (Ziegler et al., 1999, 2002, 2005;
Jonnalagadda, Ziegler, and Nelson, 2004; Leydon and Wall, 2002; Venkatraman and
Pendergast, 2002). However, it is possible for athletes who are restricting food intake
to consume a sufficient amount of some minerals if the foods chosen are highly
fortified (for example, calcium and iron added). Some of these athletes also routinely
take mineral supplements.
H. Mineral Deficiencies and Toxicities
Survival requires that the body be in a state of homeostasis, and the status of
minerals is no exception to this rule. One of the major ways the body maintains its
mineral balance is by altering either the amount absorbed, the amount excreted, or
both. In general, absorption is low or moderate for most minerals, in part, because
excretion is normally low. Most minerals can be stored in tissues, and high or low
storage levels alter the amount absorbed or excreted. For example, when iron storage
is high, absorption may drop to a low level, whereas if iron storage is low the body
can increase absorption to a small degree. High storage levels may also affect
excretion. When the body needs to limit iron intake, it may leave iron stranded in the
mucosal cells, which are sloughed off the intestinal villa and excreted. Mineral
homeostasis is maintained through the interplay of storage levels, absorption, and
excretion.
However, mineral metabolism is much more complicated than simply
adjusting intake and output. Calcium is an example of a mineral under substantial
hormonal control. Its metabolism is regulated by several hormones that influence not
only calcium absorption and excretion but also its deposition and resorption from
bone. Bone is a substantial storage site for several minerals, including calcium and
sodium. Absorption and excretion may be the bookends, but in between there are
other substantial influences such as hormones, altered metabolism, or storage capacity
that help the body maintain mineral homeostasis.
The amount of any nutrient absorbed from food depends on whether the body
is in a state of deficiency. For example, under normal conditions 70 percent of the
phosphorus consumed is absorbed. When the body is deficient in phosphorus, as is the
case of some elderly women, absorption can increase to about 90 percent. Notice that
the body tries to compensate for a deficiency by increasing absorption but that it
cannot increase absorption to 100 percent. There are limits to the body’s ability to
adapt. This is one reason mineral deficiencies occur.
Despite the body’s adaptive mechanisms, mineral deficiencies can occur if
intakes are too low over time. Any mineral deficiency will be progressive—at first
mild and difficult to detect, then moderate, and, ultimately, severe, if not detected and
treated. As with vitamin deficiencies, mild and moderate mineral deficiencies, also
called subclinical-deficiencies, often progress over a long period of time with no
visible signs or symptoms. When signs or symptoms do appear, they are usually
subtle and nonspecific.
Osteoporosis is a clinical calcium deficiency and normally develops over
many decades. Based on 2002 figures, 8 million women and 2 million men in the
United States over the age of 50 have osteoporosis (National Osteoporosis
Foundation, 2010). Loss of calcium from bone is exacerbated in women when
estrogen production declines substantially. For most women this estrogen decline is a
result of menopause, but for some female athletes, low circulating estrogen is a result
of a prolonged low caloric intake concurrent with the high energy expenditure of
intense training (see Chapter 12). Low energy availability can result in amenorrhea,
the cessation of menstruation. In two studies of amenorrheic female distance runners
between the ages of 20 and 30, 10-13 percent were diagnosed with osteoporosis.
For most of human history food was the only source of minerals. Very small
amounts of trace minerals are found in food, so there was little risk of consuming
toxic amounts from the diet. As medical research advanced, mineral deficiencies
could be detected. When a deficiency was diagnosed, it was easily reversed with
either a change in food intake or short-term mineral supplementation.
Supplementation was monitored as part of the medical treatment and toxic levels
could be avoided. The scientific focus was on one of two points on the continuum—
deficiency or toxicity.
The distance between deficiency and toxicity has been fairly well defined;
however, the difference between the amounts needed to prevent chronic diseases in
the well-nourished individual and those that result in toxicity is poorly understood and
hard to measure. The best advice for those who supplement with minerals, especially
trace minerals, is to supplement carefully and monitor dosages to avoid potential
toxicities. Fraga (2005) suggests that self-prescribed, poorly monitored intake of trace
mineral supplements will put some people on the borderline of toxicity.
I. The Roles of Minerals in Bone Formation and Blood Formation
At least eight minerals are involved in bone formation. Eighty to 90 percent of
the mineral content.of bone consists of calcium and phosphorus incorporated into
hydroxyapatite crystals, Ca,(PO,),0H. Fluoride is also incorporated, increasing the
size of the crystal and making it less fragile. However, too much fluoride makes the
crystal too large and brittle, and fragility is increased. In addition to the structural
minerals, several minerals play indirect roles. Magnesium sits on the surface of the
hydroxyapatite crystal and helps to regulate bone metabolism. Iron, zinc, and copper
are part of various enzymes that are needed to synthesize collagen.
The more than 200 bones in the body obviously are involved in skeletal
support, movement, and protection of vital organs. However, bones play other
important roles such as maintaining mineral homeostasis and acid-base balance. The
strength and hardness of bones and lack of dimensional growth in adults may lead
people to believe that bone has “finished growing” after adolescence and is not
metabolically active in adulthood. To the contrary, bone is a dynamic tissue that is
biologically active from birth throughout the entire life span.
Three major bone-related processes are growth, modeling, and remodeling.
Bones grow both longitudinally (in length) and radially (in thickness), as is evidenced
by children and adolescents who grow taller and whose bones get thicker. Modeling is
the process by which bones are reshaped, often in response to mechanical force.
Mechanical stress is placed on bones by our everyday weight-bearing activities
resisting the force of gravity and by the actions of muscles on bones during exercise.
Modeling occurs in children and adolescents and to a smaller degree in adults. For
adults, the most common of the three processes is remodeling. Remodeling is
important because “old” bone that has been microdamaged is replaced by “new”
bone, which helps to maintain bone strength. The remodeling process is also vital to
maintaining proper metabolism, such as calcium balance in the blood.
Peak mineral density (PMD) or peak bone mass refers to the highest bone
mineral density achieved during one’s lifetime. The largest amount of bone mineral is
added during childhood and adolescence. By the end of adolescence, 95 percent of the
adult skeleton has been formed; only 5 percent of bone density is accumulated
between ages 20 and 35 (Rizzoli et al., 2010). Peak bone density of trabecular bone is
achieved between the ages of 20 and 30, whereas cortical bone density peaks later,
usually between ages 30 and 35.
Achieving peak bone density is critically important because bone loss is a
natural consequence of aging. Estimates of yearly bone loss for women between the
ages of 18 and 50 years range from 0.25 to 1 percent per year (Vondracek, Hansen,
and McDermott, 2009). With the onset of menopause, estrogen deficiency results in a
yearly bone loss of 1-2 percent, initially much of it from the vertebrae. In the decade
after menopause, women can lose a total of 20-30 percent of bone density from
trabecular bone and up to 5-10 percent from cortical bone (Ilich and Kerstetter, 2000).
Older men lose bone density at a fairly constant rate of about 1 percent per year.
A favorite adage among endurance athletes is “oxygen is everything.” It is no
wonder that athletes, particularly endurance athletes, look at training and nutrition
strategies that result in optimal oxygen delivery. The nutrient most associated with
oxygen is iron. Blood consists of three types of cells—erythrocytes (red blood cells),
leukocytes (white blood cells), and platelets. This section will focus only on
erythrocytes, the blood cells whose primary function is the transport of oxygen.
Secondary functions include carbon dioxide and nitric oxide transport. Simply stated,
oxygen must be picked up from the lungs and transported to cells. Conversely, carbon
dioxide must be picked up from cells and transported to the lungs. Both of these
processes depend on hemoglobin, which transports approximately 98 percent of the
oxygen (~2 percent is dissolved in the blood plasma) and 30 percent of the carbon
dioxide (60 percent is transported as bicarbonate and 10 percent is dissolved in.blood
plasma).
Hemoglobin (heme = iron, globin = protein) is an iron-containing protein
found in the red blood cells that can bind oxygen (Figure 9.4). At the center of the
heme portion of the molecule is iron (Fe). This iron atom forms six bonds, four with
nitrogen (to maintain the molecule’s ring structure), one with the amino acids in the
protein portion of the molecule (globin), and one with oxygen. There are four heme
molecules in each molecule of hemoglobin; thus a fully saturated hemoglobin
molecule can carry four molecules of oxygen. Each red blood cell (RBC) contains
more than 250 million molecules of hemoglobin. There are approximately 30 trillion
red blood cells, so it is easy to see that the body has a phenomenal capacity for
oxygen transport.
In areas of the body where oxygen levels are high (high partial pressures of
oxygen), such as the lungs, hemoglobin has a high affinity for oxygen and is able to
bind it readily. This is important for the fast and complete diffusion of oxygen from
the lungs into the blood flowing through the pulmonary circulation. Under most
circumstances, both at rest and for most people during exercise, there is nearly 100
percent saturation of oxygen on the hemoglobin molecules in the blood that passes
through the pulmonary circulation. This is reflected in a common clinical test, the O,-
Hb saturation percentage, usually measured with a pulse oximeter or by the more
invasive blood gas analysis.
Hemoglobin measures the iron-containing protein found in red blood cells.
Values below the normal range may indicate iron deficiency anemia, a recognized
disease, or false (runner’s) anemia, which is not a true anemia. Normal hemoglobin
values are 13.8 to 17.2 g/dl for males and 12.1 to 15.1 g/dl for females. Those who
live or train at higher altitudes generally have hemoglobin concentrations nearer the
upper end of the normal range. Values below 13.8 and 12.1 g/dl, for males and
females, respectively, are usually indicative of iron deficiency anemia, but false
anemia should be ruled out. In iron deficiency anemia, the body lacks the iron it needs
to produce a normal amount of red blood cells. Hematocrit is also reduced because it
is a measure of the proportion of red blood cells in blood plasma. In false (runner's)
anemia, the slightly decreased hemoglobin value is due to plasma volume expansion
associated with endurance training.
J. The Basis of the Diet-Planning Framework
The word diet is used in two distinct ways in the English language. By
definition, a diet consists of the food and drink that a person normally consumes. Thus
each person is always “on a diet.” But the word diet is also used to describe a
restricted intake of food and drink, usually for the purpose of weight loss. Thus it is
common to hear a person say “I need to go on a diet,” “I’m on a diet,” or “I’ve gone
off my diet.” A diet is a pattern of eating. Sometimes people change their usual pattern
of eating by adopting a weight-loss diet in an effort to change body composition. This
is true for athletes, who wish to fine-tune body composition, and for sedentary people,
many of whom are overweight or obese. One's usual diet may also need to change due
to a medical condition, such as diabetes or heart disease. Changing one’s usual pattern
of eating is never easy, especially if it involves restriction.
Humans are biologically designed to be physically active. When physical
activity is high, a higher caloric diet is needed to maintain body weight. This higher
caloric intake makes it relatively simple to obtain all the nutrients needed because
larger volumes of food can be eaten. For example, a 5'7" 140 lb (170 cm 63.6 kg), 24-
year-old nonpregnant female well-trained rugby player would need ~2,500 kcal daily
to maintain energy balance and body composition. At this caloric intake it is easy to
plan a diet that meets all nutrient requirements. Although predominantly nutrient-rich
foods should be consumed to support her activity, some foods that are high in sugar
and fat and lower in nutrients can easily be incorporated into her diet plan.
An athlete’s daily energy requirement varies according to the training cycle
because energy expenditure from exercise can change considerably. The annual
training schedule of a female rower (crew) is shown in Figure 10.1. The lowest energy
expenditure (33 kcal/kg) is during the off-season, when this rower purposefully does
no training. When this athlete returns to training after the off-season, energy
expenditure increases (from 33 kcal/kg to 40 kcal/kg) _ and continues to increase as
the volume of training increases (to 44 kcal/kg). The highest energy expenditure for
the athlete in this example is during double days, when rowers engage in high-
intensity and highvolume training in both morning and afternoon practices. This is
prior to the opening of racing season and increases caloric need to more than 50
kcal/kg for a short period of time. During racing season, the total energy expenditure
is similar to the beginning of the season when the athlete returned to training (40
kcal/kg). To maintain energy balance, this rower must consume a substantial amount
of food over the 9-month training period and substantially decrease caloric intake
when training is reduced dramatically ' during the off-season. The creation of a diet
plan that has been divided into distinct periods to support training and performance is
sometimes called nutrition periodization. Each athlete should create a nutrition plan
that matches training.
Once the energy (kcal) goal has been established, the goals for macronutrients
can be considered in the proper context and a dietary prescription can be developed.
Because athletes may need higher carbohydrate and protein intakes than sedentary
individuals these two macronutrients are considered first. The athlete does not want to
compromise the intake of these important nutrients, so their energy content is
accounted for early in the diet planning process. Assume that the 24-year-old female
athlete mentioned earlier needs approximately 6 g of carbohydrate and 1.2 g of
protein per kilogram of body weight. Based on these goals, of the 2,500 kcal this
athlete wants to consume daily, ~1,768 kcal should come from carbohydrates and
proteins.
In the area of sports nutrition, the energy-containing and muscle-related
nutrients tend to be emphasized, especially carbohydrates and proteins. However, the
human body requires more than just macronutrients. For optimal performance,
training, and health, people need an array of other compounds referred to as
micronutrients. Micronutrients are substances that are needed in small quantities for
normal growth, development, and maintenance of the body, such as vitamins and
minerals (see Chapters 8 and 9). Vitamins and minerals do not contain energy so they
have no caloric value. But they are found in foods that contain carbohydrates,
proteins, and fats and are a necessary part of a healthy diet.
Processed foods that have added sugar or fat tend not to be nutrient dense
because the fat and sugar provide additional kilocalories but few or no additional
nutrients. Solid fats and added sugars are known as SoFAS. As shown in Figure 10.4,
Americans currently consume 35 percent of their total caloric intake from SoFAS and
only 65 percent from nutrient-dense foods. In contrast, the 2010 Dietary Guidelines
recommend that approximately 5-15 percent of total caloric intake should be from
SoFAS with the remaining 85-95 percent from nutrientdense foods. Consuming a
large amount of low-nutrient-dense foods daily will usually result in overconsuming
kilocalories, yet underconsuming nutrients. Thus, ironically, an obese person may be
malnourished and an athlete’s caloric intake may be too high while nutrient intake is
too low.
K. Translating Nutrient Recommendations into Food Choices
One such tool is the Food Intake Patterns developed for MyPyramid. These
intake patterns are briefly shown in Figure 10.5. (More detailed information is
available in Appendix C and at http://www.mypyramid.gov.) The foods have been
grouped according to their nutrient content. The groups are fruits, vegetables, grains,
meat and beans, milk, and oils, and the amounts of each group are adjusted based on
caloric level. Choosing minimally processed foods from these groups helps athletes
focus on a whole foods, total diet approach. These patterns are a good starting point
for use with athletes who have little nutrition knowledge.
The Food Intake Patterns developed for MyPyramid are public domain
documents and can be freely copied and distributed. Many health professionals use
these guidelines to provide basic nutrition information to consumers, some of whom
are physically active. Those who work directly with athletes in training, such as
certified strength and conditioning specialists (CSCS) and certified athletic trainers
(ATC), also use these tools to communicate basic nutrition information. This helps
athletes receive a consistent message about the importance of nutritious foods such as
fruits, vegetables, whole grains, lean proteins, beans, nuts, and hearthealthy oils.
These same types of foods will be used to plan the athlete's diet, but the amount of
food will be determined by the intensity and duration of training, and the distribution
throughout the day will depend on various factors such as timing before and after
exercise.
Many athletes can recite what has become known as the stereotypical athlete’s
dinner: broiled chicken breast without skin, plain baked potato, steamed broccoli,
whole wheat roll, nonfat milk, and fruit for dessert. Although this meal is nutritious
and does provide ample carbohydrates, proteins, and nutrients, athletes may have
difficulty coming up with ideas for other dinners that are equally nutritious and find
themselves in a food rut. They may also not like certain foods or not be able to
tolerate them. Planning and preparing varied meals is always a challenge. If they do
not already know how to do so, most athletes find that they need to learn to cook.
“Prior to exercise” is not a well-defined term, but in sports nutrition it usually
refers to an approximately 4-hour period before exercise begins. Pre-exercise,
pretraining, and precompetition meals are also terms that are used. For some athletes,
pretraining and precompetition meals are similar because training and competition are
similar. But in other cases they are remarkably different because a training session
will last for many hours but a race will be over in seconds or minutes.
Early start times of competitive events may alter the athlete’s usual eating
pattern. For example, rowers in a 2,000 m (~1'4 mile) race with a 7:00 a.m. start time
will be up at 4:00 a.m. and may not have any appetite because they are usually asleep
at this time. Eating a banana at 6:00 a.m. and sipping a sports beverage would provide
a small amount of glucose that would be quickly absorbed, but any more food or fluid
than that may be too much before high-intensity, short-duration exercise. Marathon
runners often put a sports drink and a carbohydrate snack next to their bedside and
consume it in the early hours of the morning of competition when they get up in the
night to use the bathroom. The need for trial and error, and some creativity, cannot be
overemphasized. The wrong precompetition meal can be far more detrimental ‘ than
the right precompetition meal can be beneficial!
Intake of foods and fluids during exercise is vitally important for endurance
and ultraendurance athletes, such as distance runners and cyclists, triathletes, and
adventure racers, and those who engage in intermittent, high-intensity exercise for
more than 1 hour, such as soccer and basketball players. Athletes in other sports, such
as golf, softball, or baseball, may consume food and/or fluids, but the demand for
either is less than athletes engaged in higher-intensity sports. Obviously, some athletes
cannot ingest any food or fluids during an event.
At halftime, they may. have a carbohydrate snack, such as a banana, orange, or
energy bar, and fluid. Athletes in sports such as (American) football usually
concentrate on fluid intake rather than carbohydrate intake. A track athlete who is
running a short race lasting only seconds or a few minutes does not need to be
concerned about food or fluid intake during competition, but that same athlete who
runs an individual race, is part of two relays, and performs the long jump will need to
have some carbohydrates and fluid during the track meet. Each situation is different,
and it is the intensity and duration of the exercise and the conditions under which
athletes train and compete that will primarily dictate the need for food and fluid
during training and competition.
After exercise the athlete is essentially trying to “kill four birds with one
stone,” because optimal recovery depends on replenishing carbohydrate, protein,
water, and electrolytes, particularly sodium. Some athletes choose to consume liquid
“meals,” such as specially formulated postexercise beverages, because they are
convenient and preformulated. However, other athletes prefer “real” foods that
contain both carbohydrate and protein, such as chocolate milk, yogurt with fruit in the
bottom, or cereal with milk. A turkey and cheese sandwich with salty pretzels and a
large beverage is an example of a postexercise meal that provides the four major
nutrients that an athlete who sweats heavily focuses on at the start of the recovery
period.
Caffeine is considered safe for most adults although it has several known side
effects. Blood pressure is increased both at rest and during exercise, heart rate is
increased, gastrointestinal distress can occur, and insomnia may result. The side
effects are more likely to occur in people who are caffeine naive (that is, do not
routinely consume caffeine). For routine users, some tolerance to caffeine’s effects
develops. Developing tolerance means that the user must increase the dose to produce
the desired effect. Caffeine is addictive and sudden withdrawal results in severe
headaches, drowsiness, inability to concentrate, and feelings of discontent. Addiction
has been documented with doses as low as 100 mg daily.
Caffeine and its role in performance has been well studied, and the consensus
opinion is that caffeine stimulates the central nervous system, resulting in a
heightened sense of awareness, a decreased perception of effort, and/or an increased
pain threshold (Burke, 2008; Doherty and Smith, 2005). There is scientific evidence
that caffeine consumed at an appropriate dose can enhance the performance of
distance runners, cyclists, and cross country skiers as well as runners, cyclists,
swimmers, and rowers who engage in highintensity activities lasting 1-20 minutes.
In the context of this textbook, alcohol refers to the consumption of ethanol.
Alcohol consumption is described as “drinking,” and one drink is defined as 2 0z (~15
ml) of ethanol. Three to 4 oz (90 to 120 ml) of wine, a 10 oz (300 ml) wine cooler, a
12 oz (360 ml) beer, or 112 0z (45 ml) of hard liquor (e.g., a “shot” of whiskey) each
contain approximately 2 oz (15 ml) of ethanol. Moderate alcohol intake is defined as
the consumption of up to one drink per day for women and up to two drinks per day
for men. A widely accepted definition of binge drinking is four or more drinks by a
female and five or more drinks by a male at one time. The NCAA bans alcohol use by
athletes only in the sport of rifle (NCAA Bylaw 31.2.3 Banned Drugs); however,
many colleges and universities have team rules that ban alcohol or limit its
consumption by players who are of legal drinking age. Alcohol contains 7 kcal/g, and
one “drink” typically provides ~100 to 150 kcal.
L. Dietary Supplements and Ergogenic Aids
Proper diet is fundamental to good health and athletic performance. Athletes
recognize its important roles, but many find it difficult to consume a diet that supports
training. Athletes spend millions of dollars on dietary supplements each year in the
belief that their use will help them improve their athletic performance or make them
healthier. Although some dietary supplements may have this effect, others may have
the opposite effect, resulting in impaired performance or health. Although rare, dietary
supplements | have actually contributed to or caused the deaths of some athletes.
Athletes could also unintentionally consume a banned substance because the purity of
dietary supplements can vary.
Consuming a diet that supports training and good health is a long-term
investment. Like any other longterm project, the benefits may not be evident on a day-
to-day basis. Athletes looking for a “quick fix” will not likely find it through diet
alone. One of the lures of dietary supplement use is the possibility of immediate
results. Many supplements are advertised as the newest and fastest way to enhance
performance, and the promise, hope, and hype are often hard to resist. Some dietary
supplements are also ergogenic aids. An ergogenic aid is any substance or strategy
that improves athletic performance, but the term is often used to describe substances
or techniques that increase the production of energy or the ability to do work. Many
ergogenic aids are drugs or medical procedures, such as blood doping, but some, such
as creatine, are dietary supplements.
Before consuming any dietary supplement or using any ergogenic aid, the
athlete should answer five questions: Is it legal? Is it ethical? Is it pure? Is it safe? Is it
effective? It is critical for athletes, parents, coaches, trainers, sports dietitians, exercise
physiologists, physicians, and anyone else involved in sports medicine to learn about
dietary supplements and ergogenic aids and how to address this ever-changing aspect
of athletics. Many people do not realize that dietary supplements are loosely regulated
in many countries, including the United States.
Practitioners will have little credibility with athletes if they simply dismiss the
use of dietary supplements. Regardless of the practice setting, practitioners can play a
very important role. Those with scientific training can explain the purported
physiological mechanisms and effects and discuss how a supplement might benefit or
harm the individual athlete. The complexity of the dietary supplement issue requires
that recommendations be evidence based and individually considered. Some
information is available on the label of the supplement (see Spotlight on supplements:
Understanding a Dietary Supplement Label), but the label does not include
information about safety and effectiveness. Serious discussion needs to take place to
determine if, and how much, of a supplement would be safe and effective for an
athlete to use. Such decisions should not be made on a whim by the athlete and should
not be taken lightly by the practitioner.
It is the professional's role to provide as much unbiased information as
possible to the athlete. Anyone selling a supplement is not an unbiased source of
information. Athletes should be aware that individuals who sell dietary supplements
might be involved in multilevel marketing (MLM). MLM is a form of direct sales that
allows a person (distributor) to buy a product wholesale and resell it. Sales goals may
be established, and any unsold product is costly to the distributor, so there is pressure
to sell a certain amount of product, typically to relatives, friends, and acquaintances.
Distributors may also derive income from the sales of other distributors that they have
recruited.
Vitamins and minerals are some of the most widely used supplements by
athletes, typically as a way to compensate for poor dietary intake and to avoid illness
(Petroéczi et al., 2007, 2008; Greenwood et al., 2000; Jonnalagadda, Rosenbloom, and
Skinner, 2001). But how beneficial might they be for improving nutritional health or
performance? The answer to that question depends on the athlete’s current diet and is
determined by comparing the athlete’s intake with the Dietary Reference Intakes
(DRI) for vitamins and minerals, as discussed in Chapters 8 and 9. This is a good
starting point for a discussion of dietary supplements with athletes because the need
for vitamin or mineral supplementation can be easily evaluated (see Spotlight on
supplements: Should I Take a Vitamin or Mineral Supplement?).
Botanicals are compounds that have been extracted from foods and then
concentrated in pills or tablets. Popular botanical supplements include extracts of
garlic and soy, which are used for health-related but not performance-related
purposes. Herbs are plants with nonwoody stems, and herbals are the compounds,
known as active ingredients, that are found in those plants. Some herbal supplements
have active ingredients that are not found in food, and their effects are more druglike
than foodlike. However, dietary supplements are regulated as foods, not drugs. A
monumental difference between food and drug regulation is that foods are generally
assumed to be safe until proven otherwise, whereas drugs may not be sold until the
Food and Drug Administration grants approval based on scientific data of safety and
effectiveness.
