Roles of Proteins Building material –Growth Collagen –E.g. bone or tooth »Collagen matrix...

Roles of Proteins

• Building material– Growth

• Collagen– E.g. bone or tooth

» Collagen matrix» Calcium crystals are deposited

– Ligaments and tendons– Glue holding cells together

– Maintenance• Proteins needed for new cells (skin cells

replaced every 30 days)• New proteins for growing hair and nails• Muscle cells after exercise

Copyright 2005 Wadsworth Group, a division of Thomson LearningCopyright 2005 Wadsworth Group, a division of Thomson Learning

Roles of Proteins• Enzymes

– Catalysts– Allow a reaction to happen without being

affected themselves


Roles of Proteins• Hormones

– Signalling mechanism in the body


Roles of Proteins• Regulation of fluid balance

– Edema– Proteins absorb water– If proteins accumulate in the area

around cells, they attract water causing edema

– Edema may be caused by


Roles of Proteins• Acid-base regulation

– Proteins act as buffers• A buffer is a mixture of a weak acid and its conjugate base or a weak

base and its conjugate acid.

• An acid is any molecule that can provide a H+ ion and a base is any molecule that can receive a H+ ion

• Proteins act as buffers because they tend to have both capabilities

– Acidosis, Alkalosis• Rare• Extreme cases of too much acid or base in the

blood• Can cause coma or death



Transport Proteins

Roles of Proteins• Immunity

– Antigens•Proteins, carbohydrates etc on the

surface of invading organisms like bacteria and viruses

– Antibodies•Proteins generated by the white blood

cells that can specifically recognize each and every antigen

•Helps in killing the pathogen•Basis of effectiveness of vaccines


Roles of Proteins• Source of energy

– If there is no other source of glucose, proteins will be broken down to provide glucose to the brain

– This is why fat and carbohydrate in the diet protect the protein from your body being used up

• Other roles– Structural function– Blood clotting– Vision– Wound healing


Protein Metabolism

• Nitrogen balance– Positive nitrogen balance

•More protein synthesized than degraded

•Pregnant women, infants etc

– Negative nitrogen balance•More protein degraded than produced•Burn victims, starving people etc


Protein Metabolism• Protein turnover

– Amino acid pool• The pool of amino acids in the body

– Using amino acids to make proteins

– Using amino acids to make nonessential amino acids• If there is shortage of nonessential amino acids, proteins will be

broken down to obtain essential amino acids

– Using amino acids to make other compounds• Neurotransmitters

– Using amino acids for energy and glucose• Deamination

– Removing Nitrogen– Generates ammonia --- Urea which is excreted by the kidneys

– Using amino acids to make fat• When there is excess protein – so even lean protein in excess

can lead to weight gainCopyright 2005 Wadsworth Group, a division of Thomson Learning

Copyright 2005 Wadsworth Group, a division of Thomson Learning

Protein Quality• High-quality proteins

• Digestibility– Animal vs. plant

• Amino acid composition– Limiting amino acid


Protein Quality• Reference protein

– Protein source that can support health of preschool children

– Rapid growth rate at that age

• Complementary proteins– Proteins that provide all essential amino

acids in combination


Protein Quality• PDCAAS

– Protein digestibility-corrected amino acid score

– Compares amino acids composition to human requirements and accounts for digestibility


Food Labels• Quantity of protein

– Infants -14g– Children under age four – 16g– Older children and adults – 50g– Pregnant women – 60g– Lactating women – 65g

• Daily Value– 50 g protein

•10% of a 2000 kcal diet•So if you are on a lower calorie diet

this amount would be a little less•Also the quality of the protein

needs to be considered


Recommended Intakes

• RDA– 0.8 g/kg/day– 10% - 35% of energy intake


When there is not enough protein – extreme cases

• Protein-Energy Malnutrition (PEM)• Not enough protein, energy or both• Adult PEM

– Among drug abusers (alcohol and other drugs)– AIDS or tuberculosis patients (hospital stays)– Anorexia nervosa patients

• Biggest effect on children• Acute PEM

– Short term starvation– Children are thin for their height

• Chronic PEM– Long term starvation– Children are short for their age– Seen among poor people in the world whether in Africa,

Southeast Asia or the urban poor in the US.Copyright 2005 Wadsworth Group, a division of Thomson Learning


Protein-Energy Malnutrition (PEM)

• Marasmus– “dying away”

• Kwashiorkor– “the evil spirit that infects the first child

when the second child is born”

• Marasmus-kwashiorkor mix



• Infections– Antibodies are broken down to provide

amino acids for other uses– So the body is unable to ward of infections– Dysentery (diarrhea) makes it worse since

you lose nutrient• PEM can lead to heart failure and death• Rehabilitation

– Treat diarrhea with fluids– Slowly introduce proteins and other appropriate

nutrients (as digestion improves)Copyright 2005 Wadsworth Group, a division of Thomson Learning



• The Sad Truth

Ending PEM is not a medical problemIt is a sociological and political problem


When there is not enough protein – mild cases

• Vegetarians/Vegans– It is possible to be a vegetarian and get enough

protein– Not enough good quality protein unless careful

about including multiple vegetarian protein sources– Ovo-lactovegetarians and lactovegetarians may be

fine– Vegans have the biggest problem

Vegetarian Diets


When there is too much protein

• Heart disease– High protein animal foods are also high in

fat (esp. saturated fat)– Substitute soy and other plant proteins– Elevated homocysteine levels in the blood

are associated with heart disease (homocysteine is an amino acid)

• Cancer

• Adult bone loss– osteoporosis


Health Effects• Weight control

• Kidney disease


Recommended Intakes

• Adequate intake

• Protein in abundance


Supplements• Protein supplements

• Amino acid supplements


Last few slides are from Highlight at the end of the chapter

Read appropriate sections for information regarding slides after this

one

Vegetarian Diets• Health benefits


Vegetarian Diets• Diet planning

– Protein•Lacto-ovo-vegetarians•Meat replacements

–Texturized vegetable protein


Vegetarian Diets• Vitamins and minerals

– Lactovegetarians– Vegans


Vegetarian Diets• Omega-3 fatty acids


Vegetarian Diets• Vegetarian diets through the life

span– Pregnancy and lactation– Infancy– Childhood and adolescence


Vegetarian Diets• Healthy food choices

– Macrobiotic diets


Roles of Proteins Building material –Growth Collagen –E.g. bone or tooth »Collagen matrix...

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