Chapter 004

Williams' Basic Nutrition & Diet Therapy

Chapter 4

Proteins

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14th Edition

Lesson 4.1: Proteins

1. Protein in food provides the amino acids necessary for building and maintaining body tissue.

2. Protein balance, both within the body and in the diet, is essential to life and health.

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The Nature of Proteins (p. 47)

Amino acids as basic building units Each protein is composed of hundreds of amino

acids Amino acids form unique chain sequences to form

specific proteins When protein foods are eaten, proteins are broken

down into amino acids Amino acids are reassembled in the body to form

a variety of proteins

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The Nature of Proteins (cont’d) (p. 47)

Proteins are relatively large, complex molecules May be subject to mutations or malformations

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The Nature of Proteins (cont’d) (p. 48)

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Dietary Importance (p. 47)

Amino acids Named for chemical structure Basic structure of carbon, hydrogen, and oxygen Primary source of nitrogen in diet Some contain small amounts of valuable minerals

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Classes of Amino Acids (p. 47)

Indispensable amino acids Body cannot manufacture in sufficient quantity

Dispensable amino acids Body can synthesize from indispensable

Conditionally indispensable amino acids Normally synthesized but some health conditions

may require dietary intake

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Balance (p. 49)

Protein balance Catabolism: breakdown Anabolism: resynthesis

Nitrogen balance (intake = excretion) Positive nitrogen balance: body stores more than it

excretes Negative nitrogen balance: body takes in less than

it excretes

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Functions of Proteins (p. 50)

Primary tissue building Water and pH balance Metabolism and transportation Body defense system Energy system

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Primary Tissue Building (p. 50)

Fundamental structural material of every cell Comprises bulk of:

Muscles Internal organs Brain Nerves Blood plasma

Protein repairs worn-out, wasted, or damaged tissue

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Water and pH Balance (p. 50)

Plasma proteins attract water, resulting in maintenance of normal circulation

Proteins have a unique structure to act as buffering agents

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Metabolism and Transportation (p. 51)

Enzymes Digestive enzymes: amylases, lipases, proteases

Transport agents Lipoproteins Hemoglobin

Hormones Insulin and glucagon

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Body Defense System (p. 51)

Immune system defends against disease and infection

Uses protein to build: White blood cells Antibodies

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Energy (p. 51)

May provide body fuel if the supply of carbohydrate and fat is insufficient for needs

Less efficient

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Lesson 4.2: Composition of Amino Acids

3. The quality of a protein food and its ability to meet the body’s needs are determined by the composition of amino acids.

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Food Sources of Protein (p. 51)

Complete proteins Meat, fish, poultry, seafood Soy

Incomplete proteins Plant-origin foods

• Grains• Legumes• Nuts• Seeds• Fruits and vegetables

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Vegetarian Diets (p. 51)

Must combine foods to cover all amino acid needs

Types of vegetarian diets Lacto-ovo vegetarian Lacto-vegetarian Ovo-vegetarian Vegan

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Case Study

K.C., a 32-year-old woman, wants to begin a strict vegan meal plan. She wants to make sure she eats well on this type of menu.

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Vegetarian Diets (cont’d) (p. 53)

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Case Study (cont’d)

To ensure K.C. maintains a healthy meal plan, she sets up a counseling session with the registered dietitian.

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Vegetarian Diets (cont’d) (p. 54)

Health benefits and risks Less saturated fat and cholesterol More fruits, vegetables, whole grains, other

healthful foods Lower BMI and risk of obesity Lower rate of cardiovascular disease Lower risk of renal disease Lower risk of type 2 diabetes

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Digestion of Proteins (p. 54) Mouth Stomach: enzymatic breakdown of protein by

proenzymes (zymogens) Hydrochloric acid Pepsin Rennin

Small intestine Pancreatic secretions

• Trypsin, chymotrypsin, carboxypeptidase Intestinal secretions

• Aminopeptidase, dipeptidase

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Summary of Protein Digestion (p. 57)

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Recommendations for Dietary Protein (p. 56)

Tissue growth Dietary protein quality

Chemical score (CS) Biological value (BV) Net protein utilization (NPU) Protein efficiency ratio (PER)

Additional needs caused by disease

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Recommendations for Dietary Protein (cont’d) (p. 58)

Illness or disease raise body’s need for protein Fever Catabolic tissue breakdown Traumatic injury Recovery from surgery Burns, pressure sores

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Recommendations for Dietary Protein (cont’d) (p. 58)

Dietary deficiency or excess Protein energy malnutrition

• Kwashiorkor• Marasmus

Excess protein• Usually also means excess fat intake• Protein displaces other healthy foods in diet• Extra burden on kidneys

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Dietary Guides (p. 59)

Recommended Dietary Allowances (RDAs) Relate to age, sex, weight Highest at birth and slowly declines into adulthood Men and women: 0.8 g/kg of desirable weight

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Dietary Guides (p. 59)

Dietary Reference Intakes (DRIs) from National Academy of Sciences 10% to 35% of total caloric intake from protein

(children and adults)

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Dietary Guidelines for Americans (p. 60)

High consumption of animal protein in the U.S. No benefits Some risks

• Cancer• Coronary heart disease• Kidney stones• Chronic renal failure

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Dietary Guidelines for Americans (cont’d) (p. 60)

Recommendations Choose variety of protein foods Increase amount and variety of seafood Choose proteins with less solid fats and oils

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Case Study

E.J. is 115 pounds and eats approximately 1600 calories per day

She is wondering how much protein she needs each day.

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