1. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Protein Chapter 3

2. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Protein A component of every living cell Accounts for 20% of adult weight Immune to the controversy over optimal intake

3. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Protein (cont’d) Amino acids –Basic building blocks of protein –Composed of carbon, hydrogen, oxygen, and nitrogen atoms –20 common amino acids o9 are considered essential because the body cannot make them—indispensable; they must be consumed through food o11 are considered nonessential because they can be made by the body—dispensable

4. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Essential Amino Acids Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Valine

5. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Nonessential Amino Acids Alanine Arginine Asparagine Aspartic acid Cystine (cysteine) Glutamic acid Glutamine Glycine Proline Serine Tyrosine

6. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Protein (cont’d) Protein structure –Most contain several dozen to several hundred amino acids –Shape determines function

7. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Protein (cont’d) Functions of protein –Major structural and functional component of every living cell –Body structure and framework –Enzymes –Other body secretions and fluids –Acid–base balance –Transport molecules

8. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Protein (cont’d) Functions of protein (cont’d) –Other compounds –Some amino acids have specific functions within the body –Fueling the body

9. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Amino acids are the building blocks of protein. They are classed as either essential or nonessential. Which of these is an essential amino acid? a. Glycine b. Aspartic acid c. Tyrosine d. Leucine

10. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer d. Leucine Rationale: There are 20 common amino acids, 9 of which are classified as essential or indispensable because the body cannot make them. They must be supplied through the diet. These essential amino acids include histidine, leucine, phenylalanine, and tryptophan.

11. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Protein (cont’d) How the body handles protein –Digestion oBegins in the stomach oHydrochloric acid converts pepsinogen to the active enzyme pepsin oSmall intestine is the principal site of protein digestion oEnzymes located on the surface of the cells that line the small intestine complete the digestion

12. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Protein (cont’d) How the body handles protein (cont’d) –Absorption oAmino acids, and sometimes a few dipeptides or larger peptides, are absorbed through the mucosa of the small intestine –Metabolism oLiver acts as a clearinghouse  Retains amino acids to make liver cells, nonessential amino acids, and plasma proteins such as heparin, prothrombin, and albumin  Regulates the release of amino acids into the bloodstream

13. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Protein (cont’d) Metabolism (cont’d) –Liver acts as a clearinghouse (cont’d) oRemoves the nitrogen from amino acids oConverts protein to fatty acids which form triglycerides for storage in adipose tissue oForms urea from the nitrogenous wastes of protein

14. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Protein (cont’d) Protein synthesis –Complicated but efficient process that quickly assembles amino acids into proteins the body needs –Part of what makes every individual unique is the minute differences in body proteins –Important concepts oProtein turnover

15. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Important Concepts Protein turnover Continuous process Body proteins vary in their rate of turnover Metabolic pool Contains supply of each amino acid Consists of recycled amino acids from body proteins that have broken down and also amino acids from food In a constant state of flux

16. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Important Concepts (cont’d) Nitrogen balance –Reflects the state of balance between protein breakdown and protein synthesis –Determined by comparing the amount of nitrogen consumed (intake) with the amount of nitrogen excreted (output) –Healthy adults are in neutral nitrogen balance

17. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Important Concepts (cont’d) Nitrogen balance (cont’d) –Positive nitrogen balance: when protein synthesis exceeds protein breakdown –Negative nitrogen balance: an undesirable state that occurs when protein breakdown exceeds protein synthesis

18. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Protein (cont’d) Protein catabolism for energy –Physiologic and economic waste –Overtime, loss of lean body tissue occurs –Loss of 30% of body protein causes: oImpaired breathing oAltered immune function oAltered organ function oUltimately death

19. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Is the following statement true or false? Healthy adults are in a positive state of nitrogen balance.

20. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer False. Rationale: A neutral nitrogen balance, or state of equilibrium, exists when nitrogen intake equals nitrogen excretion, indicating protein synthesis is occurring at the same rate as protein breakdown. Healthy adults are in neutral nitrogen balance.

21. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Sources of Protein Protein quality –Differs based on content of essential amino acids –Quality can become a crucial concern

22. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Sources of Protein (cont’d) Complete and incomplete proteins –Complete proteins oHigh biologic value oProvide adequate amounts and proportions of all essential amino acids needed for protein synthesis necessary to support tissue growth and repair oAnimal proteins and soy protein are complete proteins

23. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Sources of Protein (cont’d) Complete and incomplete proteins (cont’d) –Incomplete proteins oLack adequate amounts of one or more essential amino acids oExcept for soy protein, all plants are sources of incomplete proteins oGelatin is also an incomplete protein –Complementary proteins o2 proteins that when combined provide adequate amounts and proportions of all essential amino acids needed to support protein synthesis

24. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Examples of Complementary Plant Proteins Black beans and rice Bean tacos Pea soup with toast Lentil and rice curry Falafel sandwich (ground chickpeas on pita) Peanut butter sandwich Pasta e fagioli (pasta with white beans)

25. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Examples of a Plant Protein Complemented by a Small Amount of an Animal Protein to Form a Complete Protein Bread pudding Rice pudding Corn pudding Cereal and milk Macaroni and cheese Cheese fondue French toast Cheese sandwich Vegetable quiche

26. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Dietary Reference Intakes RDAs –For healthy adults is 0.8 g/kg –Acceptable macronutrient distribution range for protein for adults is 10% to 35% of total calories When the RDA does not apply –Intended for healthy people only

27. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Dietary Reference Intakes (cont’d) Protein deficiency –Protein-energy malnutrition (PEM) oKwashiorkor  Results mainly from acute critical illnesses  Aggressive nutritional support is used to restore metabolic balance as quickly as possible oMarasmus  Occurs secondary to chronic diseases  Nutritional therapy is started slowly and advanced gradually

28. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Dietary Reference Intakes (cont’d) Protein excess –No proven risks from eating an excess of protein –Conflicting data as to whether high-protein diets increase the risk of: oOsteoporosis oRenal stones

29. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Sometimes the recommended daily allowances (RDAs) do not apply to a diet. Why is this true? a. Not everyone conforms to what is considered “normal”. b. When a body is in protein excess, the RDAs do not need to be adhered to. c. The RDAs are intended for healthy people only. d. The RDAs were designed to help sick people get well.

30. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer c. The RDAs are intended for healthy people only. Rationale: The RDAs are intended for healthy people only.

31. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Protein in Health Promotion Not addressed in the Dietary Guidelines for Americans Vegetarian diets –Pure vegetarians or vegans oEat no animal products oEat only plants oThey form the smallest group of vegetarians

32. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Protein in Health Promotion (cont’d) Vegetarian diets (cont’d) –Most American vegetarians are: oLacto-vegetarians whose diets include milk products oLacto-ovo vegetarians, whose diets include milk products and eggs Nutrients of concern –Most vegetarian diets meet or exceed the RDA for protein and are nutritionally adequate across the life cycle –Iron, zinc, calcium, vitamin D, and alpha-linolenic acid are nutrients of concern

33. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Protein in Health Promotion (cont’d) Is vegetarianism for everyone? –A personal choice, subject to personal interpretation –Proper planning means paying close attention to the nutrients of concern and using a vegetarian food guide for planning

34. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins