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Chapter 4 Chapter 4 Proteins

Ahmad Adeeb

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Chapter 4Chapter 4

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Key ConceptsKey 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.

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Amino Acids: Basic Building Amino Acids: Basic Building MaterialMaterial

• Each protein is made up 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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Classes of Amino AcidsClasses of Amino Acids

1-Indispensable amino acids “ عنه غنى ”ال Body cannot synthesize

2-Dispensable amino acids“ اساسي “غير Body can synthesize

***Conditionally indispensable amino acids Normally synthesized but some health

conditions may require dietary intake

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A Healthy BalanceA Healthy Balance

• Protein balance Catabolism: breakdown Anabolism: resynthesis

• Nitrogen balance 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 ProteinFunctions of Protein

• Tissue building

• Energy

• Water balance

• Metabolism

• Body defense system

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Notes Notes

• 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.

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Food Sources of ProteinFood Sources of Protein

• Complete proteins Meat Soy

• Incomplete proteins Plant-origin foods• Grains حبوب

• Legumes النبات قرون• Nuts

• Seedsبذور• Fruits and vegetables

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Vegetarian DietsVegetarian Diets

• Must combine foods to cover all amino acid needs

• Health benefits & risk

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Digestion of ProteinsDigestion of Proteins

• Mouth

• Stomach: enzymatic breakdown of protein by proenzymes (zymogens) Pepsin Hydrochloric acid Rennin ” in child”

• Small intestine Pancreatic secretions Intestinal secretions

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Body Needs for ProteinBody Needs for Protein

• Tissue growth needs

• Dietary protein quality Chemical score (CS) Biological value (BV)

• Additional needs due to disease

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Dietary Deficiency or ExcessDietary Deficiency or Excess

• Protein-energy malnutrition Kwashiorkor Marasmus

• Excess protein Usually means excess fat intake also Protein displaces other healthy foods in diet Kidneys stressed Potential calcium loss

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Dietary GuidesDietary Guides

• Recommended Dietary Allowances (RDAs) Relate to age, sex, weight

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

(children and adults)

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Protein NeedsProtein Needs

• Assumes individual consumes 2200 kcal per day; based on recommendation of 10% to 35% of total kcalories from protein

• 2200 kcal x 0.10 – 0.35 = 220 – 770 kcal per day from protein

• 220 – 770 kcal 4 kcal/g = 55 – 192.5g of protein per day