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Protein ch6
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  • 1. Protein
  • 2. Protein Basics
    • Amino acids = building blocks of proteins
      • 20 kinds, but only 9 are essential amino acids (EAA)
        • Phenylalanine, valine, tryptophan, methionine, threonine, histidine, isoleucine, leucine, lysine
      • EAA needs approx. 11% of total protein intake
        • Typical diet supplies 50% as EAA
        • Children have higher need for EAA, need high-quality protein in diet
    • Each amino acid contains carbon, hydrogen, and nitrogen
  • 3. Amino Acids
    • Each amino acid contains an “R” group
      • Specialized side-group
      • Examples:
        • Branch-chain amino acids (BCAA) have carbon and hydrogen “R” groups and can be used to make glucose if little or no CHO is consumed in the diet
          • Leucine, isoleucine, valine
        • PKU (phenylketonuria) – disease caused by inability to convert “R” group of phenylalanine to form tyrosine
  • 4. Page 211
  • 5. Amino Acids to Protein
    • Amino acids are connected via peptide bonds
      • Dipeptide
      • Tripeptide
      • Polypeptide
  • 6. Protein Digestion
    • Denaturation = change in shape
      • Heat, acid, alkali, agitation can denature proteins and deactivate them
    • Cooking denatures protein
      • Makes tough connective tissue softer, easier to chew, swallow, digest
      • Kills bacteria
      • Inactivates some biologically active proteins
  • 7. Fig. 6.7
  • 8. Fig. 6.10
  • 9. Protein Digestion
    • Stomach – begins digestion of protein
      • Acid denatures protein
      • Pepsin breaks polypeptides into smaller peptides
    • Small intestine - most protein digestion and absorption occurs here
      • Pancreatic juice contains proteases which complete digestion of peptides
      • Single amino acids and some di- and tripeptides are absorbed
  • 10. Synthesizing Protein
    • DNA = genetic code for all proteins made by the body
    • Change in amino acid  change in protein shape (and function)
      • Ex: sickle cell anemia
    Fig. 6.3
  • 11. Protein Turnover
    • Protein turnover = constant synthesis and breakdown of protein
      • Allows cells to adapt to changes in body circumstances
      • Amino acids are easily recycled, so we do not need to eat as much protein
    • If amino acid used for energy, made into glucose, or lost due to cell breakdown, waste product ammonia is produced
      • Liver turns ammonia into urea which is filtered by kidneys for excretion
  • 12. Protein Functions in the Body
    • Structure
      • Collagen – structural protein found in bones, skin
      • Keratin – structural protein found in hair, nails
    • Acid-base balance
      • Some proteins act as buffers (resist pH change)
  • 13. Protein Functions in the Body
    • Oncotic pressure
      • Presence of protein in small blood vessels attract water back into blood, partially counteracting blood pressure
        • If low protein in diet, too much fluid accumulates in tissues = edema
        • Hypertension, congestive heart failure, preeclampsia
    Fig. 6.9
  • 14. Thinking Time
    • What affect would a drop in pH (more acidic) have on body proteins?
    • Why might an elderly adult with a poor appetite have edema in her feet and ankles?
  • 15. Protein Functions in the Body
    • Hormones
      • Thyroid hormone, insulin, glucagon, growth hormone
    • Enzymes
      • Almost all are proteins or contain protein
    • Immune system
      • Antibodies are proteins
    • Energy
      • If low on CHO, liver and kidneys make glucose from BCAA
      • If starving, amino acids can be used for energy  muscle and organ wasting
  • 16. Thinking Time
    • Why does a patient with a poor appetite have a higher risk for infection?
    • Why do enzymes and hormones from animal or plant foods not adversely affect our bodies?
  • 17. Complete vs. Incomplete Protein
    • High-quality/Complete
      • Source: animal protein
      • Contains all 9 essential amino acids
    • Lower-quality/Incomplete
      • Source: plant protein
      • Missing at least 1 essential amino acid
      • Limiting amino acid = essential amino acid missing from protein food or in body
      • Complementary protein = plant protein that contains limiting amino acid of another plant protein
  • 18. Fig. 6.13
  • 19.  
  • 20. Vegetarianism
    • Types of vegetarianism:
      • Vegan = strict vegetarian
        • No animal products in diet
      • Lacto-ovo-vegetarian = consumes milk and egg products but no meat
      • Piscevegetarian – consumes fish but no other meat products
      • Pollovegetarian – consumes poultry but no red meat
  • 21. Vegetarianism
    • Health reasons
      • Generally lower risk for cardiovascular disease
        • Less saturated fat, no or little cholesterol, low sodium
        • More fiber, phytochemicals
    • Moral/ethical reasons
    • Financial reasons
  • 22. Legumes
    • Legumes provide an excellent source of protein (although incomplete protein)
      • Limiting amino acid = methionine
    • Also good source of fiber, vitamins and minerals
    • Digestive difficulty due to medium-chain length fibers that are fermented by bacteria in large intestine  gas, acid production
  • 23. Legumes
    • Beano – enzyme formula that may reduce gas production
    • Small servings
    • Start with split peas, limas, lentils
    • Dry bean prep:
      • Cook in boiling water for 3 min, turn off heat, cover, soak 2-3 hours, pour off water, use fresh water for cooking
    • Canned bean prep:
      • Pour off water, rinse well
  • 24. Soy
    • FDA approved health claim for lowering cholesterol because of soy protein
      • 25 grams/day
    • Sources: tofu, soymilk, soyflour, tempeh, miso, soynuts, edemame
    • Isoflavones in soy have possible health benefits:
      • Decrease menopause symptoms, osteoporosis risk, some cancer growth
  • 25. Protein Needs
    • Need to balance protein lost from breakdown (can be determined by urea in urine)
    • If growing, pregnant/lactating, or recovering from illness, need more protein
    • RDA: 0.8 grams/kg
      • 8-10% of total kcal intake
      • 46-56 grams/day needed vs. 65-100 grams actual intake!
    • Excess protein intake  amino acids stripped of nitrogen (converted to urea) and carbon skeleton stores as fat
  • 26. Protein-Energy Malnutrition
    • Marasmus – very inadequate protein and energy intake
      • Means “to waste away”
      • “ Skin and bones” appearance
      • Commonly seen in infants and young children not breastfed, weaned too early, or have water diluting formula
    • Kwashiorkor – very inadequate protein, marginal or adequate caloric intake
      • Marked edema, especially in belly
      • “ The evil spirit the first child gets when the next child is born”
  • 27. Fig. 6.12
  • 28. High-protein Diets
    • Pros:
      • Provide extra vitamin B6, iron, zinc
    • Cons:
      • May indicate low plant food intake  decreased fiber, vitamins, some minerals, no phytochemicals
      • Associated with cardiovascular disease risk (likely due to saturated fat intake)
      • High red meat consumption associated with colon cancer risk
      • Extra burden on kidneys to excrete excess nitrogen
      • Toxicity from certain amino acids if taken in large amounts (supplements)
  • 29. Supplementation
    • Amino acid supplements
      • Popular ergogenic aids in sports
      • Decrease absorption of similar amino acids
      • May lead to limiting amino acid situation in body
      • Little evidence that they are beneficial to athletes (except for endurance sports)