Protein

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Protein


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Nitrogen Cycle

• Plants use N2 to make a.as and proteins
• Animals eat plants
• Humans consume plants and animals
• Decomposed organic matter puts N2 back into soil
  to be use by plants

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Protein

• Structure
• Building block of all proteins is the amino acid
• Contains carbon, hydrogen, oxygen, nitrogen
• Polypeptides made of 100-300 aas
• Eg leucine, alanine, serine etc

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Protein synthesis

• Amino acids join with a peptide bond
• Peptide bond formed between
• Carboxyl OH group of 1st amino acid
• Nitrogen group of 2nd amino acid
• Polypeptide
• Protein unit that contains many peptide bonds

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Amino acids

• 9 essential amino acids
• 11 non-essential a.a.
• Long chains of amino acids make up different
  proteins
• Potential for endless combinations of amino acids

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Non-essential a.a.

• Can be made in the body from essential a.a. or
  from other non-essential amino acids or be
  supplied by body proteins
• Most foods except fruit, vegetables and fats
  contain protein
• Non-animal products are a significant source of
  protein

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Essential amino acids

• The body cannot synthesise these from other amino
  acids
• Must be provided in the diet or own body proteins
  will be used
• Meat, poultry, fish, eggs, dairy products and
  soya beans

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Functions of PROTEIN

• Growth, maintenance and repair of all body cells
• Replacement
• Fluid balance
• Acid base balance
• antibodies
• Hormones
• Transport proteins
• enzymes
• Source of energy

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Examples of body proteins

• Collagen and elastin skin
• Keratin hair
• Albumin blood
• Hemoglobin red blood cells
• Insulin hormone
• Lipase, protease enzymes
• DNA and RNA genetic material

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Digestion, absorption and use

• Peptide chain straightened to allow access for
  enzymes
• Broken down to single a.a.
• Transported via blood to cells
• Held in a.a. pool for up to eight hours
• Converted to fat unless used for cell repair or
  energy

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Protein Quality

• Animal protein
• Wine, vinegar, salt, acid, heat denatures
  proteins, loosening bonds making it more tender
• Denaturing proteins makes them more available to
  digestive enzymes for absorption
• Vegetable Protein
• Less well digested
• Encased cell walls thus need to be cooked
• Contain enzymes that interfere with protein
  digestion

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Reference Protein

• Eggs
• Most complete and digestible protein
• Used as a standard for measuring protein quality
• Protein Quality
• BV (Biological Value)
• BV amount of protein nitrogen that is retained
  for growth and maintenance

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Health effects of protein

• Protein Deficiency
• Poor growth in children
• Weight loss and wasting in adults
• Two conditions
• Marasmus
• Kwashiorkor

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Risks with high protein intake

• Excess energy intake
• May limit CHO intake
• Increased need for water
• Calcium losses
• ? Stress on the kidneys

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RDI and Intakes

• RDIs
• Men 19-64 yrs
• 55g/day
• Women 19-54 yrs
• 45g/day

• Protein intake in NZ
• 15 yrs plus
• 105g/day
• 15 of energy
• 15yrs plus
• 71g/day
• 16 of energy

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Estimating protein needs

• To maintain protein balance in the body, the best
  estimate of protein required for nearly all
  adults is 0.8g/kg body weight
• When might the body be in positive balance ?
• When might the body be in negative balance ?

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Food sources of protein

• Animal meats (beef, chicken, fish etc), eggs,
  milk and milk products
• Vegetable legumes (dried beans, peas and
  lentils), nuts, seeds, grains eg rice, corn etc
• NZ Diet -beef and veal 14, bread 11, milk 10,
  poultry 7, seafood 7.

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Vegetarian diets

• Vegetarian diets with no animal products can
  supply all the essential amino acids
• Most vegetable proteins are only short of one
  a.a. the limiting a.a.
• The limiting a.a. can be supplied by another
  vegetable protein
• Knowledge of food combinations important

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Example

• Wheat is low in lysine but served with dried
  beans, rich in lysine (limiting in methionine)
  can provide the correct balance of all essential
  aas.

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Protein content of food

• 1 Bagel 6 grams 4 fish fingers 9
• 1 cup Muesli 15 1 meat pie 13
• 1 cup porridge 4 1 cup hot chips 9.5
• 1 cup Soya milk 8 1 sausage roll 10
• 1 cup pasta 4.5 100 g gurnard 26.5
• 1 cup brown rice 5.5 100 g tuna 23
• 100 g cheese 25 100 g fillet steak 27
• 100 g cottage cheese 15 100 g chicken breast 25
• 1 cup ice cream 6 100 g lamb 26
• 1 cup milk 8.5-11 100 g turkey breast 29
• 1 pot yoghurt 7 100 g luncheon 11
• 1 hamburger 15 100 g mussels 23
• 1 Big Mac 27 100 g peanut butter 29
• 1 cup coleslaw 4 1 Mars bar 3.2
• 100 g cauliflower 2 1 cup lentils 10

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Practical advice

• Protein should be provided by wide range of
  available foods, including lean meat, chicken and
  seafood, eggs and milk. Bread is also important
  source. Include some vegetable sources too.
• Choose low fat options of meat and milk products.
• If vegetarian, choose protein from diverse plant
  sources (legumes, nuts, breads, cereals etc.) If
  lacto-ovo vegetarian, include eggs and milk
  products.

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