Nutrition

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Chapter 7: Protein

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Amino Acids

  • Building blocks of protein

  • Contain
  • Nitrogen group (amine)
  • Acid group (carboxyl group)
  • Hydrogen
  • Side chain (R-portion)
  • Determines protein name
  • Sometimes sulfur

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Amino Acids

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Amino Acids

  • 20 Total
  • 9 Essential
  • 11 Non-essential
  • Some conditionally essential
  • Essential during infancy, disease or trauma

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Conditionally (Semi)-Essential Amino Acids

EAA: methionine --> (semi EAA): cysteine

EAA: phenylalanine --> (semi EAA): tyrosine

If cysteine and tyrosine are not consumed

in the diet, methionine and phenylalanine will be used to make them.

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Phenylketonuria

Phenylalanine Tyrosine

(Essential AA) phenylalanine hydroxylase (Nonessential AA)

“ MISSING; LACKING”

Control Intake Becomes essential

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Synthesis of
Non-essential Amino Acids

  • How are we able to make these?

  • Transamination Reactions

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Transamination

Process of transferring an amine group from one AA to a carbon skeleton to form a new AA

Produce NEAA’s

Enzymes used in these reactions are termed aminotransferases

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Figure 07_03

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“Generic” Transamination

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Common Transaminations

glutamate + pyruvate -ketoglutarate + alanine

glutamate + OAA -ketoglutarate + aspartate

Alanine

Transaminase

Aspartate

Transaminase

Glutamic acid and α-ketoglutarate, an intermediate in the Krebs cycle, are interconvertible by transamination. Glutamic acid can therefore enter the Krebs cycle for energy metabolism, and be converted by the enzyme glutamine synthetase into glutamine, which is one of the key players in nitrogen metabolism.

Aspartic acid has an alpha keto homolog which is oxaloacetate

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Deamination

  • Removal of an amine group from an AA
  • Some Aas lose their amine group w/o transferring to a carbon skeleton
  • Amine group needs to be excreted as it forms ammonia
  • Ammonia (NH3) incorporated into urea in the liver via the urea cycle
  • Urea travels through bloodstream to kidneys and is excreted in urine

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Figure 07_03

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Disposal of Excess Amino Group

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Deamination

  • Carbon skeleton can then be:
  • Burned for energy
  • Synthesized in fatty acids – stored in adipose tissue
  • Converted to glucose (gluconeogenesis)

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Synthesis of Proteins

  • Amino Acids connected by peptide bonds
  • Dipeptide; Tripeptide
  • Oligopeptide: 4-9 AA linked together
  • Polypeptide: >10 (50-100) AA linked together
  • Proteins
  • Most proteins in food are large polypeptides (>100)
  • Major part of lean body mass

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Synthesis of Proteins

  • Determined by gene expression
  • DNA code transferred from nucleus to cytosol via mRNA
  • Transcription phase
  • Forming mRNA from portion of DNA
  • Translation phase
  • Synthesis of polypeptide chains by ribosomes based on data contained in mRNA
  • DNA determines shape and function of proteins

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Text art 07_03

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Proteins

  • What determines their function?

  • Sequence, shape, and structure

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Structure

  • Primary
  • Sequence of AA
  • Secondary
  • Bends and folds held together by bonds
  • Tertiary
  • 3-D shape
  • Quaternary
  • 2 or more proteins interacting together

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Example

  • Sequential order of AA is imperative for a proteins’ function
  • Only 1 AA out of sequence can result in major structural malformation
  • Sickle Cell Disease

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Figure 07_06

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Denaturation and Adaptation

  • Denaturation of Protein
  • Altering protein’s 3 dimensional structure
  • Acid, alkaline, heat, enzymes and agitation

  • Adaptation of Protein Synthesis
  • Constant state of breakdown, rebuilding and repair
  • Protein turnover

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Turnover and Metabolism

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Sources of Protein

  • Diet and recycling of body protein
  • North America
  • 70% supplied by meat, poultry, fish, milk and milk products, legumes and nuts
  • Worldwide
  • 35% of protein comes from animal
  • Incorporate more plant protein

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Protein Quality

  • Ability of a food protein to support body growth and maintenance
  • Measured under condition that protein intake is adequate but NOT excessive
  • Protein exceeding this amount is used less efficiently

  • High quality protein or complete protein

  • Low quality protein or incomplete protein

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Protein Quality

Measured by the following:

  • Biologic value
  • Protein efficiency ratio
  • Chemical score of protein
  • Protein Digestibility Corrected Amino Acid Score (PDCAAS)

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Biological Value

  • Measure of how efficiently a food protein can be turned into body tissues
  • If contains all 9 EAAs, should be able to efficiently incorporate the food protein into body proteins

  • Egg white has highest BV 100
  • All nitrogen that is absorbed is retained

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Protein RDA

  • Adults
  • .8g/kg healthy body weight

  • Recovery states
  • .8 –2 g/kg body weight

  • Endurance or strength athletes
  • .8 –1.7 g/kg body weight

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RDA for Protein

  • Promotes equilibrium
  • 0.8 g of protein / kg of healthy body weight

154 lb = 70 kg

2.2 lb/kg

70 kg x 0.8 g protein = 56 g protein

kg healthy body wt

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RDA for Protein

  • Protein needs increase in the following:
  • Growth
  • Pregnancy
  • Endurance, strength athletes
  • Wound healing

  • About 10-35% of total kcal
  • Most of us eat more than the RDA for protein
  • Excess protein cannot be stored as protein

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2.unknown

Nitrogen Balance

Positive Nitrogen balance:

  • State in which nitrogen intake exceeds nitrogen losses
  • Growth, pregnancy, recovery after illness, athletic training (body building)

Negative Nitrogen balance:

  • State in which nitrogen losses from the body exceed intake
  • Poor intake, fever, burns, infections, PEM, kidney disease, prolonged bed rest
  • Results in loss of LBM

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Nitrogen Balance

  • To determine the balance between protein gain and loss

.16 x protein = N Protein = N x 6.25

N balance = 24 h protein Intake - [24 hr UUN + 4 g*]

6.25 g

N loss in the urine Other N

losses

*Estimates insensible losses of nitrogen (fecal, dermal, hair, sweat, GI, etc.)

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Digestion and Absorption

  • Stomach
  • Proteins denatured by stomach acid (pH ~2)
  • Gastrin stimulates release of pepsinogen from the chief cells in stomach

  • Pepsinogen converted to pepsin by acid in stomach
  • Pepsinogen (proenzyme)  pepsin

  • Pepsin breaks peptide bonds—larger proteins to smaller polypeptides

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Digestion and Absorption

  • Small Intestine
  • Protein stimulates release of GIP, CCK

Pancreatic enzymes (proteases) secreted into small intestine

Protein digestion completed in the small intestine

All polypeptides hydrolyzed into di, tri peptides, AA

Trypsinogen  Trypsin

Chymotrysinogen  Chymotrypsins

Procarboxypeptidases  Carboxypeptidases

Di, tripeptidases, aminopeptidases

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Digestion and Absorption

  • Di- and tripeptides, amino acids
  • Broken down into AA in intestinal wall before entering circulation
  • Absorbed into portal vein
  • Transported to liver
  • Resynthesized into proteins, albumin synthesis, gluconeogenesis, fat, energy
  • Enter general circulation

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Digestion and Absorption

  • Whole proteins not absorbed
  • Exception during infancy
  • Immature GI tract
  • Absorption of intact proteins can contribute to development of food allergies

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Figure 07_12

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Functions of Proteins

  • Producing Vital Body Structures
  • Maintaining Fluid Balance
  • Edema
  • Contributing to Acid Base Balance
  • Buffers
  • Forming Hormones, Enzymes and Neurotransmitters

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Functions of Proteins

  • Contributing to Immune Function
  • Anergy is immune incompetence
  • Transporting Nutrients
  • Forming Glucose
  • Gluconeogenesis
  • Muscle wasting is cachexia
  • Providing Energy
  • 4 kcal/gm

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Health Concerns

  • Protein- Energy Malnutrition (PEM)
  • Marasmus
  • Minimal amounts of energy, protein and other nutrients
  • Kwashiorker
  • Minimal amounts of protein and moderate energy deficit
  • High Protein Diets

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Protein-Energy Malnutrition (PEM)

  • One of the most prevalent forms of malnutrition in the world

  • Affects >500 million children worldwide

  • In the US:
  • Homeless people, those living in substandard housing in inner cities, rural areas

  • Hospitalized people with chronic diseases (cancer, pulmonary problems), AIDS, trauma, severe infections

  • People suffering from anorexia nervosa

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Kwashiorkor

  • Diet is low in protein compared to energy intake
  • Person may have  energy needs due to infection
  • Sometimes seen in sick people in the hospital
  • Signs/symptoms:

Diarrhea Fatigue

Growth failure Infections

Edema Dry flaky skin

LBM loss

Fatty liver

Multiple vitamin, mineral and electrolyte deficiencies

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Marasmus

  • Diet is very low in protein AND energy (and all other nutrients)
  • “Skin and bones” appearance
  • No subcutaneous fat

  • May occur in:
  • Infants whose formula is over-diluted
  • People with anorexia nervosa

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Figure 07_15

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Marasmus

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Protein-Energy Malnutrition (PEM)

  • Results in
  • Poor growth (children, infants)
  • Weight loss (adults)
  • Poor immune function and more infections
  • Poor wound healing

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Is a High-Protein Diet Harmful?

  • High in:
  • total fat, saturated fat, and cholesterol

 risk of heart disease

  • Low in:
  • fiber, vitamins, phytochemicals
  • Can cause ketosis, esp if inadequate in CHO
  • Burden on the kidney, increased calcium loss

  • High protein from food up to ~3.0 gm/kg probably has no severe long term health consequences
  • No Upper Limit for protein

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High Protein Diets

  • People on high protein diets are encouraged to drink more fluid to help excrete the extra nitrogen produced as a result of protein/amino acid metabolism

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Food Protein Allergies

  • Prevalence is increasing
  • Most common allergens: 90% of all
  • Peanuts, tree nuts ( > 3 years)
  • Milk* products ( > 1 year)
  • Soy* (> 6 months)
  • Wheat* (> 6 months)
  • Eggs* (egg whites > 2 years)
  • Fish, shellfish (> 3 years)
  • * = more likely to be outgrown with age

Vegetarianism

  • Vegans
  • Excludes all foods of animal origin
  • Lactovegetarians
  • Includes milk and milk products
  • Lactoovovegetarians
  • Includes milk, milk products and eggs
  • Semi-vegetarian

Exclude meat (beef, pork, lamb) but will eat seafood, poultry, dairy

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Factors Influencing One’s Decision to Become a Vegetarian

Health reasons

Religious beliefs

Concern for environment

Concern for cruelty to animals

Financial

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Health Benefits

Vegetarian diets tend to be:

High in fiber, antioxidants and phytochemicals

Lower in saturated fat, cholesterol, total fat

Vegetarians, in general, have less:

Obesity, CVD, hyperlipidemia, hypertension, Type 2 diabetes, constipation, diverticulosis

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Potential Nutrient Inadequacies with Vegan Diets

Greatest risk to infants, growing children (growth retardation), pregnant women

B12

Vitamin D

Calcium

Iron

Zinc

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Iron

  • Beef is best source
  • Iron deficiency anemia
  • Take a multivitamin with iron, eat iron fortified foods

Vitamin B12

  • Found only in animal sources
  • Pernicious anemia
  • Consume B12 fortified foods, take a multivitamin with B12

Calcium, Vitamin D

  • Milk & milk products are our best source
  • Increased risk for osteoporosis
  • Consume calcium fortified foods, take a calcium & Vitamin D supplement

Zinc

  • Primarily in red meat, fish
  • Zinc deficiency can cause growth retardation, contribute to poor

wound healing

  • Eat plenty of whole grains, take a multivitamin with zinc

Potential Nutrient Deficiencies

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Terminology

Complete protein

  • A dietary protein containing all the EAA’s
  • Foods of animal origin

Incomplete protein

  • Protein which does not have all of the EAA’s in adequate amounts for protein synthesis
  • Plant foods

Complementary proteins

  • 2 or more proteins whose amino acid make-up complement each other in such a way that the EAA missing from one is supplied by the other

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Complementary Protein

Food 1 Food 2

CC CCCC

AAAA AA CAR CAR CAR

RRR RRR CAR CAR CAR

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Peanut butter (incomplete protein): high in lysine

Bread: low in lysine (limiting AA)

Put them together  PB sandwich which is a complete protein

(complementary protein)

Complementary Proteins

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Other Examples of Complementary Food Combinations

Beans and rice

Bean burrito

Split pea soup with bread

Curried lentils and rice

Stir fried tofu and vegetables over rice

Corn tortilla with beans

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Servings

Group

Lactovegetarian

Vegan

Key Nutrients Supplied

Grains

6 – 11

8 – 11

Protein, thiamin, niacin, folate, vitamin E, zinc, magnesium, iron, and dietary fiber

Legumes

1 – 2

2

Protein, vitamin B-6, zinc, magnesium, and dietary fiber

Nuts, seeds

1 – 2

2

Protein, vitamin E, and magnesium

Vegetables

3 – 5 (include one dark green or leafy variety daily)

4 – 6 (include one dark green or leafy variety daily)

Vitamin A, vitamin C, and folate

Fruits

2 – 4

4

Vitamin A, vitamin C, and folate

Milk

2 – 3

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Protein, riboflavin, vitamin D, vitamin B-12, and calcium

Soy Nutrition

Soy foods contain:

Protein

Fiber

Calcium

Isoflavones (genistein, daidzein), saponins, lignans, phytosterols, and other phytochemicals

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  • Isoflavones and other phytochemicals
  • May protect against hormone-related cancers
  • Breast, prostate, endometrial

  • Lowers the level of LDL cholesterol
  • When substituted for animal protein in the diet

  • Soy foods may reduce calcium loss from bones

  • Soy may ease menopausal symptoms
  • More research needed here

Soy Nutrition

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Soy Foods

Tofu

Tempeh

Textured vegetable protein (TVP)

Soy milk

Soy nuts

Soy milk, soy beans,

tofu

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Soy Foods

Grams of soy protein

Tofu, 4 oz 13

Soy burger , 1 12

Soy milk. 1 cup 6-10

Roasted soy nuts, ½ cup 20

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Soy Recommendations

  • 25 gm per day

  • Obtain from foods for most benefit (rather than supplements)

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Servings

Group Lactovegetarian Vegan Key Nutrients Supplied

Grains 6 – 11 8 – 11 Protein, thiamin, niacin, folate,

vitamin E, zinc, magnesium, iron,

and dietary fiber

Legumes 1 – 2 2 Protein, vitamin B-6, zinc,

magnesium, and dietary fiber

Nuts, seeds 1 – 2 2 Protein, vitamin E, and

magnesium

Vegetables 3 – 5 (include

one dark green

or leafy variety

daily)

4 – 6 (include

one dark green

or leafy variety

daily)

Vitamin A, vitamin C, and folate

Fruits 2 – 4 4 Vitamin A, vitamin C, and folate

Milk 2 – 3 -- Protein, riboflavin, vitamin D,

vitamin B-12, and calcium