Part II: Diet Analysis
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mmmm.docxChapter 4
Carbohydrates
Chapter 4
Carbohydrates
Big Idea
Whole grains are an energy source with nutritional punch.
You likely eat grains every day—cereal, a sandwich, pasta, or your favorite rice dish.
Whole grains are vital to a healthful diet. In addition to fiber, whole grains offer
other slow-releasing carbohydrates, antioxidants, vitamins, and minerals, all of
which are needed for good health. Maybe you are on a diet and have been told to
limit or restrict your carbohydrate intake. How much is too much and which
carbohydrates are better for you? Can you promote a healthy weight with a
balanced intake of whole grains? Before we answer these questions, let’s examine in
brief the history of grain.
In ancient times whole grains were cracked open using quern stones that required
hours of hand labor. As technology slowly advanced, the quern stone was modified
into the millstone. It wasn’t until the advent of water wheels that human labor to
produce grains was reduced. About 2,500 years ago the Romans started milling flour
by turning one millstone wheel against another that did not move. The turning was
done by animals, slaves, and later by waterwheels. The process of milling breaks the
hard outer bran coat of the wheat seeds. The bran and germ, which contain the
majority of fiber, vitamins, and minerals, are removed by sifting. In the earliest
days, the whitest flour was chosen to make bread for the wealthy, and the coarsest
was given to the poor. One’s economic status was depicted by the color of brea
they ate. Wheat was the grain of choice for many cultures, as it not only produced
white flour but also contained gluten which gives wheat bread its elasticity and
lightness in texture. The word “flour” comes from a French word meaning
“blossom” and is metaphoric for the finest part of the meal. Bakers highly prized
their art and it was kept from the masses. In fact the baker’s mark was one of the
first trademarks
they ate. Wheat was the grain of choice for many cultures, as it not only produced
white flour but also contained gluten which gives wheat bread its elasticity and
lightness in texture. The word “flour” comes from a French word meaning
“blossom” and is metaphoric for the finest part of the meal. Bakers highly prized
their art and it was kept from the masses. In fact the baker’s mark was one of the
first trademarks.
In America, Oliver Evans built the first flour mill, which was powered by a
watermill. It used a series of elevators that moved grain through the mill, cleaning
it first, then grinding and sifting it. Today, modern milling produces three types of
flour; whole meal containing 100 percent of the grain, with nothing added or
removed; brown flour, containing 85 percent of the original grain with some bran
and germ and white flour, containing 75 percent of the wheat grain with the most
bran and germ removed. The vast majority of flour milled and used in foods and
cooking in America is white flour. The modern milling process of preparing white
flour removes between 50 and 85 percent of B vitamins, vitamin E, calcium, iron,
potassium, chromium, phosphorus, zinc, magnesium manganese, and coba
In the early nineteenth century several diseases stemming from vitamin and
mineral deficiencies, such as pellagra (niacin, B
3
), beriberi (thiamine, B
1
), and
anemia (iron), plagued many inhabitants of the nation. One of the first public health
campaigns was to improve the health of Americans by enriching flour, a dietary
staple. The B vitamins, niacin, thiamine, riboflavin, and folate were added along
with iron to combat dietary deficiencies and proved a successful strategy to
improve public health. However, enriched flour contains only 6 percent or less of
the recommended daily intake of the vitamins and minerals it “replaces.”
Overwhelming scientific evidence now shows that diets containing high amounts of
whole grains rather than refined white flour decrease weight gain and the risk for
many chronic diseases, including certain types of cancer and diabetes. Whole grains
contain a whole nutrient package that is not replaced by enriched flour. Consumers
are becoming more aware of the many health benefits of whole grains. However,
the food industry has created a puzzle for consumers in determining if a product is
made from 100 percent whole grains. “Whole wheat” does not always mean the
product is made with 100 percent whole grains, and brown breads are not always
healthier than white as the color may come from added caramel. The Food and Drug
Administration (FDA) has provided the food industry with specifics on how to label
whole-grain foods—to label it as made from 100 percent whole grains. The best
method to ensure the product is made from 100 percent whole grains is to check
the ingredient list. One-hundred percent whole-grain products list whole grains or
whole-wheat flour most often as the first ingredient and do not contain wheat flour,
white flour, yellow corn flour, semolina flour, degerminated flour, or durum flour.
In America, whole-grain choices are improving, but progress still needs to be made
on reducing the added sugar content of many industrially prepared breads,
assuring added fiber comes from good sources, eliminating ambiguous labels and
claims on packaging, and reducing the costs of whole-grain breads, which still
exceed that of white bread
hat Exactly Are Carbohydrates and How Many Types Are There?
Carbohydrates are the perfect nutrient to meet your body’s nutritional needs. They
nourish your brain and nervous system, provide energy to all of your cells (and
within proper caloric limits), and help keep your body fit and lean. Specifically,
digestible carbohydrates provide bulk in foods, vitamins, and minerals, while
indigestible carbohydrates provide a good amount of fiber with a host of other
health benefits.
Plants synthesize the fast-releasing carbohydrate, glucose, from carbon dioxide in
the air and water, and by harnessing the sun’s energy. Recall from
Chapter 3
"Nutrition and the Human Body"
that plants convert the energy in sunlight to
chemical energy in the molecule, glucose. Plants use glucose to make other larger,
more slow-releasing carbohydrates. When we eat plants we harvest the energy of
glucose to support life’s processes
Carbohydrates are a group of organic compounds containing a ratio of one carbon
atom to two hydrogen atoms to one oxygen atom. Basically, they are hydrated
carbons. The word “carbo” means carbon and “hydrate” means water.
Glucose
1
, the
most abundant carbohydrate in the human body, has six carbon atoms, twelve
hydrogen atoms, and six oxygen atoms. The chemical formula for glucose is written
as C
6
H
12
O
6
. Synonymous with the term carbohydrate is the Greek word
“saccharide,” which means sugar. The simplest unit of a carbohydrate is a
monosaccharide
2
. Carbohydrates are broadly classified into two subgroups, “fast-
releasing” and “slow-releasing.” Fast-releasing carbohydrates are further grouped
into the monosaccharides and dissacharides. Slow-releasing carbohydrates are long
chains of monosaccharides.
Fast-Releasing Carbohydrates
Fast-releasing carbohydrates are also known more simply as “sugars.” Fast-
releasing carbohydrates are grouped as either monosaccharides or dissacharide
Monosaccharides
For all organisms from bacteria to plants to animals, glucose is the preferred fuel
source. The brain is completely dependent on glucose as its energy source (except
during extreme starvation conditions). The monosaccharide galactose differs from
glucose only in that a hydroxyl (−OH) group faces in a different direction on the
number four carbon. This small structural
alteration causes galactose to be less
stable than glucose. As a result, the liver
rapidly converts it to glucose. Most
absorbed galactose is utilized for energy
production in cells after its conversion to
glucose. (Galactose is one of two simple
sugars that are bound together to make
up the sugar found in milk. It is later freed
during the digestion process.)
Fructose also has the same chemical formula as glucose but differs in its chemical
structure, as the ring structure contains only five carbons and not six. Fructose, in
contrast to glucose, is not an energy source for other cells
in the body. Mostly
found in fruits, honey, and sugarcane, fructose is one of the
most common
monosaccharides in nature. It is also found in soft drinks, cereals,
and other
products sweetened with high fructose corn syru
Less common monosaccharides are the pentoses, which have only five carbons and
not six. The pentoses are abundant in the nucleic acids RNA and DNA, and also as
components of fiber.
Lastly, there are the sugar alcohols, which are industrially synthesized derivatives
of monosaccharides. Some examples of sugar alcohols are sorbitol, xylitol, and
glycerol. (Xylitol is similar in sweetness as table sugar.) Sugar alcohols are often
used in place of table sugar to sweeten foods as they are incompletely digested and
absorbed, and therefore less caloric. The bacteria in your mouth opposes them,
hence sugar alcohols do not cause tooth decay. Interestingly, the sensation of
“coolness” that occurs when chewing gum that contains sugar alcohols comes from
them dissolving in the mouth, a chemical reaction that requires heat from the
inside of the mouth.
Disaccharides
Disaccharides
3
are composed of pairs of two monosaccharides linked together.
Disaccharides include sucrose, lactose, and maltose. All of the disaccharides contain
at least one glucose molecule.
Sucrose, which contains both glucose and fructose molecules, is otherwise known as
table sugar. Sucrose is also found in many fruits and vegetables, and at high
concentrations in sugar beets and sugar cane, which are used to make table sugar.
Lactose, which is commonly known as milk sugar, is composed of one glucose unit
and one galactose unit. Lactose is prevalent in dairy products such as milk, yogurt,
and cheese. Maltose consists of two glucose molecules bonded together. It is a
common breakdown product of plant starches and is rarely found in foods as a
disaccharide.
Slow-Releasing Carbohydrates
Slow-releasing carbohydrates are
polysaccharides
4
, long chains of
monosaccharides that may be branched or not branched. There are two main
groups of polysaccharides: starches and fibers.
Starches
Starch molecules are found in abundance in grains, legumes, and root vegetables,
such as potatoes. Amylose, a plant starch, is a linear chain containing hundreds of
glucose units. Amylopectin, another plant starch, is a branched chain containing
thousands of glucose units. These large starch molecules form crystals and are the
energy-storing molecules of plants. These two starch molecules (amylose and
3. Two monosaccharides joined
together.
4. A long chain of
monosaccharides that may be
branched or not branched.
Chapter 4 Carbohydrates
4.1 A Closer Look at Carbohydrates
172
amylopectine) are contained together in foods, but the smaller one, amylose, is
more abundant. Eating raw foods containing starches provides very little energy as
the digestive system has a hard time breaking them down. Cooking breaks down the
crystal structure of starches, making them much easier to break down in the human
body. The starches that remain intact throughout digestion are called resistant
starches. Bacteria in the gut can break some of these down and may benefit
gastrointestinal health. Isolated and modified starches are used widely in the food
industry and during cooking as food thickeners.
Humans and animals store glucose energy from starches in the form of the very
large molecule,
glycogen
5
. It has many branches that allow it to break down quickly
when energy is needed by cells in the body. It is predominantly found in liver and
muscle tissue in animals.
Dietary Fibers
Dietary fibers
6
are polysaccharides that are highly branched and cross-linked.
Some dietary fibers are pectin, gums, cellulose, and lignin. Humans do not produce
the enzymes that can break down dietary fiber; however, bacteria in the large
intestine (colon) do. Dietary fibers are very beneficial to our health. The Dietary
Guidelines Advisory Committee states that there is enough scientific evidence to
support that diets high in fiber reduce the risk for obesity and diabetes, which are
primary risk factors for cardiovascular disease.US Department of Agriculture. “Part
D. Section 5: Carbohydrates.” In
Report of the DGAC on the
Dietary Guidelines for
Americans, 2010. Accessed September 30, 2011.
http://www.cnpp.usda.gov/
Publications/DietaryGuidelines/2010/DGAC/Report/D-5-Carbohydrates.pdf
. Dietary
5. A highly branched
macromolecule consisting of
thousands of glucose
monomers held together by
chemical bonds.
6. Polysaccharides that are highly
branched and cross-linked and
only found in plant-based
foods, with the exception of
chitin (which forms the
exoskeletons of some animals).
Chapter 4 Carbohydrates
4.1 A Closer Look at Carbohydrates
173
Image removed due to copyright restrictions
fiber is categorized as either water-soluble or insoluble. Some examples of soluble
fibers are inulin, pectin, and guar gum and they are found in peas, beans, oats,
barley, and rye. Cellulose and lignin are insoluble fibers and a few dietary sources of
them are whole-grain foods, flax, cauliflower, and avocados. Cellulose is the most
abundant fiber in plants, making up the cell walls and providing structure. Soluble
fibers are more easily accessible to bacterial enzymes in the large intestine so they
can be broken down to a greater extent than insoluble fibers, but even some
breakdown of cellulose and other insoluble fibers occurs.
The last class of fiber is functional fiber. Functional fibers have been added to foods
and have been shown to provide health benefits to humans. Functional fibers may
be extracted from plants and purified or synthetically made. An example of a
functional fiber is psyllium-seed husk. Scientific studies show that consuming
psyllium-seed husk reduces blood-cholesterol levels and this health claim has been
approved by the FDA. Total dietary fiber intake is the sum of dietary fiber and
functional fiber consumed.
KEY TAKEAWAYS
• Carbohydrates are a group of organic compounds containing a ratio of
one carbon atom to two hydrogen atoms to one oxygen atom.
Carbohydrates are broadly classified into two subgroups, fast-releasing
and slow-releasing carbohydrates.
• Fast-releasing carbohydrates are sugars and they include the
monosaccharides and disaccharides. Slow-releasing carbohydrates
include the polysaccharides, amylose, amylopectin, glycogen, dietary
fiber, and functional fiber.
• Glucose is the most important monosaccharide in human nutrition.
Many other monosaccharides and disaccharides become glucose in the
body.
• Fiber-rich foods are scientifically proven to reduce the risk of obesity
and diabetes. Functional fibers are added to foods because they are
proven to have added health benefits.
Chapter 4 Carbohydrates
4.1 A Closer Look at Carbohydrates
174
Hight Gi 69
Medium Gi 56-69
Low Gi 56
Sweeteners with Trade
Name
Calories
Source/Origin
Consumer
Recommendations
Controversial Issues
Product Uses
& interest
groups
• warning
label
listed on
products
about
saccharin
and
cancer
risk in
animals
until 2001
when
studies
concluded
that it did
not cause
cancer in
humans
Acesulfame K
• Sunnette
• Sweet One
0 kcal/g
Discovered in
1967.
Composed of
an organic
salt, potassium
(K). Structure
is very similar
to saccharin’s.
It passes
through the
body
unchanged
which means
it does not
ADI: 15 mg/kg
body weight.
Body cannot
digest it.
*Can be used in
cooking.
Chewing gum,
powdered
beverage
mixes,
nondairy
creamers,
gelatins,
puddings,
instant teas
and coffees.
Chapter 4 Carbohydrates
4.7 The Food Industry: Functional Attributes of Carbohydrates and the Use of Sugar Substitutes
224
Sweeteners with Trade
Name
Calories
Source/Origin
Consumer
Recommendations
Controversial Issues
Product Uses
provide
energy.
Two hundred
times sweeter
than sucrose.
Cyclamates
• Sugar Twin
(Canada
only)
0 kcal/g
Thirty times
sweeter than
sucrose.
Discovered in
1937.
No ADI available.
1949, cyclamate
approved by FDA for
use. Cyclamate was
classified as GRAS
(Generally Recognized
As Safe) until 1970
when it was removed
from GRAS status and
banned from use in
all
food and beverage
products within the
United States on the
basis of one study that
indicated it caused
bladder cancer in rats.
Approval still pending
for use in the United
States since the ban.
Canada and other
countries use this type
of sweetener.
Recommended
as a substitute
for table sugar
for diabetics in
1950s, baked
goods.
Sucralose
• Splenda
1
Splenda
packet
contains
3.31
First
discovered in
1976.
Approved for
use in 1998 in
ADI: 5 mg/kg
body weight.
General
purpose
sweetener,
baked goods,
beverages,
Chapter 4 Carbohydrates
4.7 The Food Industry: Functional Attributes of Carbohydrates and the Use of Sugar Substitutes
225
Sweeteners with Trade
Name
Calories
Source/Origin
Consumer
Recommendations
Controversial Issues
Product Uses
calories
= 1g
the United
States and in
1991 in
Canada.
Derived from
sucrose in
which three of
its hydroxyl
(OH) groups
are replaced
by chlorine
(Cl−).
Six hundred
times sweeter
than sugar.
*Can be used in
cooking.
gelatin
desserts,
frozen dairy
desserts,
canned fruits,
salad
dressings,
dietary
supplements;
currently
recommended
as a
replacement
for table sugar
and additive
for diabetics.
Stevioside
• Stevia
• Sweet Leaf
N/A
Derived from
stevia plant
found in South
America.
Stevia
rebaudianan
leaves.
Classified as
GRAS.
Considered to be
a dietary
supplement and
approved not as
an additive, but
as a dietary
supplement.
Used sparingly, stevia
may do little harm,
but FDA could not
approve extensive use
of this sweetener due
to concerns regarding
its effect on
reproduction, cancer
development, and
energy metabolism.
Sold in health
food stores as a
dietary
supplement.
Sucrose
• Sugar
~4 kcal/
g
Extracted
from either
sugar beets or
sugar cane,
which is then
It is illegal to sell
true raw sugar in
the United States
because when
raw it contains
Over-consumption has
been linked to several
health effects such
as
tooth decay or dental
caries and contributes
Biscuits,
cookies, cakes,
pies, candy
canes, ice
cream, sorbets,
Chapter 4 Carbohydrates
4.7 The Food Industry: Functional Attributes of Carbohydrates and the Use of Sugar Substitutes
226
Chapter 5
Lipids
of
Inuit. The Inuit were fishers and hunters, primarily of sea mammals such as
whales,
walruses, and seals. They consumed a high-protein, high-fat diet. In fact,
the Inuit
consumed an average of 75 percent of their daily energy intake from
fat.Patricia Gadsby,
“The Inuit Paradox,” Discover
, 1 October 2004.
http://discovermagazine.com/2004/oct/inuit-paradox/article_print
.
Stefansson’s
research focused on the fact that the Inuit diet had no adverse effects on either
their
health or his own.Lieb, C. W. “The Effects of an Exclusive Long-Continued Meat
Diet.”
JAMA
87, no. 1 (1926): 25–26. doi:10.1001/jama.1926.02680010025006
These findings were supported by a later study in 1972, when the Greenland Inuit
first caught the attention of Dr. H. O. Bang from Aalborg University in Denmark. He
noted that although the Inuit consumed massive amounts of fatty ocean fish, which
are packed with omega-3s, none of the Inuit tested showed signs of heart disease. In
addition, there was significantly less evidence of joint disease and skin disease than
found in Western countries. Further research led Bang and his associate, Dyerberg,
to conclude that the omega-3 fatty acids (docosahexaenoic acid, or DHA, and
eicosapentaenoic acid, or EPA) present in the diet offer significant heal
Heart disease.
Further research supports Bang and Dyerberg’s finding
and shows DHA and EPA to be beneficial to heart health and human
development. EPA and DHA tend to reduce blood pressure, prevent
blood-clot formation (thereby reducing the risk of stroke), and protect
against irregular heartbeats.
•
Inflammation and autoimmune diseases.
According to research
published in the
Journal of the American College of Nutrition
, animal
experiments and clinical intervention studies indicate that omega-3
fatty acids have anti-inflammatory properties.Sears, B. “Anti-
Inflammatory Diets for Obesity and Diabetes.”
J Am Coll Nutr
21 (2008).
The low incidence of autoimmune and inflammatory disorders such as
psoriasis, asthma, and Type 1 diabetes and the complete absence of
multiple sclerosis has been observed and studied in the Inuit
population in Greenland.Brzezinski, A. “Review.”
Gastroenterol Hepatol
3, no. 10 (2007): 787–88.
http://www.ncbi.nlm.nih.gov/pmc/articles/
PMC3104160/
. Subsequent studies concur with these findings and it is
believed that omega-3 fats play an important role in the prevention
and treatment of coronary artery disease, high blood pressure,
arthritis, other inflammatory and autoimmune disorders, and
cancer.Simopoulos, A. “Omega-3 Fatty Acids in Inflammation and
Autoimmune Diseases.”
J Am Coll Nutr
21, no. 6 (2002): 495–505.
http://www.jacn.org/content/21/6/495.full
.
•
Brain health.
Omega-3 fats play an important role in maintaining
mental health and are crucial for brain function. Omega-3 fatty acids
may provide benefits such as expanding learning and memory
capacities. Early evidence suggests that the consumption of omega-3
fats is essential for synaptic transmission in the brain. Furthermore,
omega-3 fats seem to be most effective when obtained from foods
rather than from supplements.
You Decide
What sources of omega-3 fatty acids would you include in your diet and why?
As you read further, you will learn the different types of fats, their essential roles in
the body, and the potential health consequences and benefits of diets rich in
Chapter 5 Lipids
234
particular lipids. You will be better equipped to decide the best way to get your
nutritional punch from various fats in your diet.
5.1 What Are Lipids?
LEARNING OBJECTIVE
1. Explain the role of lipids in overall health.
Lipids are important fats that serve different roles in the human body. A common
misconception is that fat is simply fattening. However, fat is probably the reason we
are all here. Throughout history, there have been many instances when food was
scarce. Our ability to store excess caloric energy as fat for future usage allowed us
to continue as a species during these times of famine. So, normal fat reserves are a
signal that metabolic processes are efficient and a person is healthy.
Lipids are a family of organic compounds that are mostly insoluble in water.
Composed of fats and oils, lipids are molecules that yield high energy and have a
chemical composition mainly of carbon, hydrogen, and oxygen. Lipids perform
three primary biological functions within the body: they serve as structural
components of cell membranes, function as energy storehouses, and function as
important signaling molecules.
The three main types of lipids are triacylglycerols, phospholipids, and sterols.
Triacylglycerols (also known as triglycerides) make up more than 95 percent of
lipids in the diet and are commonly found in fried foods, vegetable oil, butter,
whole milk, cheese, cream cheese, and some meats. Naturally occurring
triacylglycerols are found in many foods, including avocados, olives, corn, and nuts.
We commonly call the triacylglycerols in our food “fats” and “oils.” Fats are lipids
that are solid at room temperature, whereas oils are liquid. As with most fats,
triacylglycerols do not dissolve in water. The terms fats, oils, and triacylglycerols
are discretionary and can be used interchangeably. In this chapter when we use the
word fat, we are referring to triacylglycerols.
Phospholipids
1
make up only about 2 percent of dietary lipids. They are water-
soluble and are found in both plants and animals. Phospholipids are crucial for
building the protective barrier, or membrane, around your body’s cells. In fact,
phospholipids are synthesized in the body to form cell and organelle membranes. In
blood and body fluids, phospholipids form structures in which fat is enclosed and
transported throughout the bloodstream.
1. The second most common of
the three basic lipids. Similar
to triacylglycerols,
phospholipids have an acid
containing phosphorus in place
of one of the fatty acids. These
lipids appear in all cell
membranes.
Chapter 5 Lipids
236
Sterols are the least common type of lipid. Cholesterol is perhaps the best well-
known sterol. Though cholesterol has a notorious reputation, the body gets only a
small amount of its cholesterol through food—the body produces most of it.
Cholesterol is an important component of the cell membrane and is required for the
synthesis of sex hormones, vitamin D, and bile salts.
Later in this chapter, we will examine each of these lipids in more detail and
discover how their different structures function to keep your body working.
The Functions of Lipids in the Body
Storing Energy
The excess energy from the food we eat is digested and incorporated into
adipose
tissue
2
, or fatty tissue. Most of the energy required by the human body is provided
by carbohydrates and lipids. As discussed in
Chapter 4 "Carbohydrates"
, glucose is
stored in the body as glycogen. While glycogen provides a ready source of energy,
lipids primarily function as an energy reserve. As you may recall, glycogen is quite
bulky with heavy water content, thus the body cannot store too much for lon
