Chapter 4 Protein

1. Chapter 4 Protein

2. Objectives Identify the: nature of protein functions of protein identify the food sources of protein body needs of protein digestion of protein dietary protein requirements

3. Key concepts • Food proteins provide the amino acids necessary for building and maintaining body tissue • Protein balance, both within the body and in the diet, is essential to life and health • The quality of a protein food, and its ability to meet the body’s needs, is determined by the composition of amino acids

4. Definitions Amino Acids: Nitrogen-bearing compounds that form the structural units of protein Digested proteins yield their specific amino acids Conditionally indispensable amino acids: The body can make these. However, under certain circumstances such as illness, the body cannot make them in high enough quantities and they become indispensible in the diet.

5. Nature of Proteins • Amino Acids are the basic building material • Joined in unique chain sequences to form specific proteins • When digested, the various food proteins yield their constituent amino acids, which are then available for use by cells

6. Amino acids: basic building material Role as building units- All protein is made up of amino acids Each amino acid is joined by a peptide bond

7. Amino Acid(s) cont. • Two amino acids joined together are called a dipeptide. • Polypeptides are chains of up to 100 amino acids • Hundreds of amino acids are linked together to form a single protein.

8. Amino Acids: Basic building material Dietary importance- Amino acids are named for their chemical nature. Amino refers to the compound containing nitrogen Fats and carbohydrates have carbon, hydrogen and oxygen but no nitrogen Protein is 16% nitrogen – the primary source of nitrogen in the body

9. Amino acids

10. Classes of amino acids There are 20 common amino acids which are vital to human life and health: indispensable dispensable conditionally indispensable Indispensable amino acids- the body cannot manufacture them in sufficient quantity or at all Indispensable = necessary in the diet; cannot be left out Nine of them

11. Classes of Amino Acids Dispensable Amino Acids: Note: This term “dispensable” can be misleading. All amino acids have essential tissue building and metabolic functions. The five amino acids can be synthesized from other amino acids and thus, are not necessary in the diet.

12. Classes of Amino Acids Conditionally Indispensable: Under certain physiological conditions, the 6 amino acids, which are normally synthesized in the body like the dispensable amino acids, must be consumed in the diet.

14. Balance Concept: Refers to the relative intake and output of substances in the body to maintain equilibrium Necessary for health throughout life Can be applied to the life-sustaining protein and the nitrogen that it supplies

15. Balance Protein Balance- Proteins being broken down into amino acids is called catabolism, and then Resynthesized into tissue proteins as needed. This process is called anabolism The body also maintains a balance between tissue protein and plasma protein, which are further balanced with dietary protein intake

16. Nitrogen balance – indicates how well its tissues are being maintained- intake of protein in diet vs amount of nitrogen excreted in urine –also known as state of equilibrium or protein balance 1g urinary protein (nitrogen) = digestion and metabolism of 6.25 g of dietary protein At different times in life or states of illness or malnutrition, the balance may shift to + or – nitrogen balance Balance

17. Balance Positive nitrogen balance: • takes in more protein than excretes- storing extra protein in tissues E.g. during periods of rapid growth, pregnancy, lactation as well as in individuals who have been ill and are “building back up” with increased nourishment.

18. Balance Negative nitrogen balance: • takes in less protein than excreted- In children protein deficiency can cause growth retardation Can be due to inadequate protein intake Losing Nitrogen by breaking down more tissue than it is building up. E.g. Illness, malnutrition [Kwashiorkor]

19. Positive nitrogen balance

20. Functions of Protein Primarily tissue building- Largest portion of the body (except for water) is made up of protein. Body protein accounts for about ¾ of the dry matter in most tissue (exceptions: bone, adipose) Primary functions are to repair worn-out, wasted, or damaged tissue and build up new tissue

21. Functions of Protein Additional body functions of protein: Energy system- back up source for energy when there is an insufficient supply of CHO & fat Water balance – Plasma protein, especially albumin, help maintain water balance

22. Functions of Protein Metabolism- Protein aids metabolic function through enzymes, transport agents, and hormones Body defense system – Protein helps build special WBCs (lymphocytes) and antibodies as part of the body’s immune system to defend against disease and infections

23. Food Sources of Protein Types of food proteins – Food contains a mixture of proteins that complement each other- Key to balanced diet is variety: animal and plant sources Complete proteins = Protein foods that contain all 9 essential amino acids; found primarily in animal source, eggs, milk and cheese. Note: Soy products are the only plant source of complete protein Incomplete proteins – Protein food that are missing one or more of the nine indispensable amino acids. These proteins are generally of plant origin – e.g. seeds, vegetables, fruits

25. Vegetarian Diets Complementary Protein: A mixture of plant proteins can provide adequate amounts of amino acids when the basic use of various grains is expanded to include soy protein and other dried legume proteins (e.g. beans, peas) Matching plant foods so that the amino acids missing in one food are supplied in another This is the art of combining plant protein foods so that they “complement” one another and supply all 9 indispensable amino acids

26. Vegetarian Diets Types of vegetarian diets Lacto-ovo vegetarians – Eggs and dairy ok Lacto-vegetarians – Dairy ok, no eggs Ovo-vegetarians – Eggs ok, no dairy Vegans- No eggs or dairy, no animal products at all – only plant foods

27. Vegetarian Diets The most recent position paper from the American Dietetic Association and Dieticians of Canada states that a vegetarian diet, including vegan, can meet the current recommendations for all essential nutrients, including protein and that vegetarian diets are appropriate throughout all stages of life.

28. Health benefits and risk Lower levels of dietary saturated fat and cholesterol from animal fat Higher levels of CHO, fiber, Mg+, Boron, folate, phytochemicals, Vitamin C, E Lower body mass index and prevalence of obesity Lower death rates from heart disease, hypercholesterolemia, and hypertension Lower risk of Type II DM Lower risk of some forms of cancer (prostate, colon) Lower risk of dementia

29. Vegetarian Diet • For the most part this diet is considered an inexpensive and safe approach to prevent modern lifestyle diseases

30. Digestion of Proteins Mouth – Mechanical part of digestion is chewing Particles are mixed with saliva and passed on to the stomach as a semisolid mass Stomach - chemical digestion begins here Proteins are large and complex- All enzymes needed for break down of protein are stored in an inactive form called proenzymes or zymogens [which are activated upon need]. Can not store in active form or will break down walls of the stomach and intestines.

31. Digestion of Protein Stomach – 3 agents in gastric secretion help with chemical digestion: • Hydrochloric acid – converts pepsinogen to pepsin and also begins unfolding and denaturing of the complex protein chains. When they are unfolded it makes them more available for enzymatic action

32. Digestion of Protein (stomach cont’d) • Pepsin – Main gastric enzyme, stored as pepsinogen hydrochloric acid converts pepsinogen to pepsin which begins splitting the links of proteins and amino acids into short chains called peptides.

33. Digestion of Protein (stomach cont’d) • Rennin – Gastric enzyme in infancy and childhood- Important to digestion of milk. Rennin with Ca act on the casein of milk to produce a curd. Rennin prevents milk from moving too fast from stomach to small intestines by creating this curd

34. Digestion of Protein Small intestine – protein digestion starts in the acid environment of the stomach and is finished in the alkaline environment of the intestines. Pancreatic secretions break down protein to simpler and simpler substances: Trypsin, Enterokinase, Chymotrypsin, Carboxypeptidase

35. Digestion of Protein Intestinal secretions – Glands in the intestinal wall produce two more protein-splitting enzymes to complete the digestion process Aminopeptidase and Dipeptidase

36. Partial protein digestion by the enzyme pepsin and stomach acid • Further protein digestion by enzymes released by pancreas • Final digestion of protein to amino acids take place mostly inside cells of small intestine • Amino acids absorbed into the portal vein and transported to the liver. From here they enter the general blood stream. • Little dietary protein is present in the feces.

37. Recommendations for Dietary Protein Protein requirements: influencing factors Tissue growth needs – fetal growth, infant growth, lactation, adolescent growth and development Dietary protein quality – Four basic measures to determine protein quality (p. 55) Chemical score (CS Biological Value (BV) Net Protein Utilization (NPU) Protein efficiency ratio (PER) intake Illness or disease – fever and catabolism (increased tissue breakdown), increases body’s need for protein

38. Dietary Deficiency Protein-energy malnutrition (PEM) – Most severe cases are found in less industrialized countries where not only protein-rich foods are in short supply but all foods are. Children are at highest risk because of elevated needs during rapid growth and development Other persons at risk: Elderly Poor nutrition Disease or infection AIDS Cancer Liver Failure

39. Dietary Deficiency Two severe forms: Kwashiorkor – Common 18 – 24 month old- taken off breast because of new baby and put on high carbohydrate diet. Kwashiorkor is a Ghanian word that refers to a disease that takes over the child when the second child is born. A child may receive adequate total kcal but lack enough kcals from protein Marasmus – Very emaciated, low body fat, Chronic form of protein deficiency – basic starvation. Affects individuals of all ages; usually due to inadequate food sources

41. Excess Dietary Protein The body has a finite need for protein. Additional protein is stored as fat or used as energy after nitrogen is removed Problems with high-protein diets can include: May be high in saturated fats if unbalanced May increase risk for cardiovascular disease Kidneys may have to work overtime to rid the body of excess nitrogen Excess protein may increase calcium losses in the bone when dietary calcium is inadequate over the long term May risk nutritional deficiency if other food groups are limited or eliminated

42. Dietary Guidelines 10% - 35 % of total caloric intake from protein Example: To calculate the protein needs of an individual consuming 2000 kcal per day based on the DRI of 10-35% of total kcal: 2000 Kcal x .10 - .35 = 200 – 700 Kcal per day 200 – 700 /4 Kcal/g = 50 – 175 g protein per day Example: To calculate the protein needs of a female with a body weight of 125 lbs.: [ 0.8g of high quality protein/kg body wt./day (2.2 lbs = 1 kg) 125 lbs / 2.2lbs/kg = 56.81 kg. 56.81 x 0.8g/kg = 45.45 g protein /day