Protein

• Proteins

  • Proteins are large compounds made up of carbon, hydrogen, oxygen, and nitrogen atoms
  • Only source of nitrogen for the body
  • These atoms link together to form different amino acids which are the building blocks of protein chains
  • There are 20 different amino acids that make up protein and each protein has a unique sequence of amino acids
  • Each amino acid has a different structure
• Amino acids

  • Central carbon atom bonded to one hydrogen atom, an amino group (NH2) and a carboxylic acid group (COOH)
  • It's the fourth attachment (known as a side group) that distinguishes the difference between each amino acid changing the acid's shape and size
• Types of amino acids

  • Essential
  • Non-essential
  • Conditional
• Essential amino acids


  9 of the 20 amino acids that cannot be synthesised (made) by the body or cannot be produced in sufficient amounts and therefore need to be consumed in the diet
• Non-essential amino acids

  • The remaining 11 amino acids that can be synthesised by the body and are termed non essential amino acids
  • Non essential amino acids may become essential under certain circumstances, such as illness, injury, stress, or rapid growing stages and are referred to as conditionally essential
  • In children, arginine is a conditionally essential amino acid required for optimal growth and development, and it must therefore be provided by the diet and for adults if experiencing trauma, injury, or renal failure
• Conditionally essential amino acids

  Non-essential amino acids that may become essential under certain circumstances, such as illness, injury, stress or rapid growing stages
• Conditionally essential amino acids

  • Arginine
• 7 non-EAAs that become conditionally essential

  • Arginine
  • Cysteine
  • Glutamine
  • Glycine
  • Proline
  • Serine
  • Tyrosine
• Complete proteins


  • High Biological Value
  • Contain all nine essential amino acids - general animal foods
• Incomplete proteins

  • Low biological value
  • Lack one or more of the nine essential amino acids - generally plant foods
• Complementary proteins

  The combination of two incomplete proteins that together contain all the essential amino acids
• Protein sources classified as

  • Complete
  • Incomplete
  • Complementary
• Limiting amino acids


  The amino acid that is present in the lowest amount in a protein source, which limits protein synthesis
• Limiting amino acids in plant proteins

  • Lysine in wheat, corn and rice
  • Methionine in many legumes including kidney beans, chickpeas, peas and lentils
• Complete Protein sources

  • Dairy products (milk, cheese, yoghurt)
  • Meat (beef, lamb)
  • Poultry (chicken, turkey)
  • Seafood (fish, tuna, prawns)
  • Eggs and Egg products (chicken eggs, mayonnaise, pancakes, breaded fried foods)
  • Small goods (salami, ham, bacon, peperoni)
• Gelatine


  The only animal product that is not a complete protein as it does not contain all the nine essential amino acids (tryptophan)
• Quinoa, buckwheat, chia seeds, soy products


  The only plant products that contain all nine essential amino acids
• Vegetarian diet types

  • Vegan
  • Vegetarian
  • Lacto-Vegetarian
  • Lacto-Ovo Vegetarian
• Vegan


  Avoid eating all animal products and foods
• Vegetarian


  A 'loose' term to describe people who do not eat animal foods
• Lacto-Vegetarian

  Avoid meat and eggs, but include dairy products
• Lacto-Ovo Vegetarian


  Avoid eating all animal products, but will consume milk, milk products and eggs
• • Vitamin B12 and iron are concerns for a poorly balanced vegetarian diet
  • To ensure essential amino acids are consumed , people need to consume complementary proteins.
  • Eat foods from two different food sources within the same meal. E.g. cereals with legumes
• Complementary proteins

  • Two or more incomplete proteins that can be combined to ensure each essential amino acid is consumed, as they have different limiting amino acids
  • Two or more incomplete proteins can be combined to ensure each essential amino acid is consumed.
  • Individually they have different limiting amino acids and are of LBV, but when combined they are considered HBV sources.
  • Nachos (corn & kidney beans)
  • Minestrone Soup (legumes & vegetables)
  • Combining two different sources of plant protein allows the amino acids to complement one another.
• Complementary proteins

  • Nachos (corn & kidney beans)
  • Minestrone Soup (legumes & vegetables)
• Novel protein foods (NPFs)


  • Products based on vegetable protein and micro-organisms that are produced from sources that are widely available but not commonly consumed
  • Some novel protein sources such as insects, algae, duckweed, microbial protein, leaf protein and rapeseed are expected to enter the market as replacements for animal derived protein sources.
• Novel protein sources

  • Seitan, tofu, soy meat, tempeh, quorn, meatless based on lupin beans, insects, algae, duckweed, microbial protein, leaf protein, rapeseed
• Amino acids are linked together in a variety of sequences to make different proteins required by the body
• Peptide bond


  Bonds that link each amino acid, forming a polypeptide chain
• Condensation reaction


  The reaction that completes the formation of the polypeptide chain
• Functions of proteins

  • Structural: required for growth, maintenance & repair of body tissues
  • Functional: required for synthesis of enzymes, hormones, antibodies, stabilising DNA/RNA, enabling muscle contraction and movement, acting as transporters, maintaining fluid balance, providing secondary energy source
• Protein provides 16.7kJ/g of energy
• Recommended protein intake

  • 15-25% of the total daily energy intake should come from protein
  • Women require 0.75g of protein/kg of body weight
  • Men require 0.84g of protein/kg of body weight
  • Pregnant women and men and women over 70 require 1g of protein/kg of body weight
• Insufficient protein intake can lead to failure to thrive/faltering growth, slow healing of wounds, decreased immunity, anaemia due to insufficient haemoglobin
• Kwashiorkor


  A condition found in developing countries where there is a deficiency in the quality and quantity of dietary protein, with symptoms including wasted muscles, protuberant belly, brittle hair and failure to grow, peeling skin and apathy
• Marasmus


  A condition that occurs when both protein and energy (kJ) are in short supply, with symptoms including faltering growth in children, extreme muscle wastage, sunken eyes, and general debility
• Nitrogen balance


  The balance between anabolism (build up) and catabolism (break down)
• Newborn screening tests for conditions like phenylketonuria and galactosemia
• Phenylketonuria is an inborn error of metabolism on phenylalanine that can cause mental disabilities, behavioural issues, skin rash, and musty body odour
• • Galactosemia is a rare, hereditary disorder of carbohydrate metabolism that affects the body's ability to convert galactose to glucose
  • Galactose is a sugar contained in milk, including human mother's milk as well as other diary products. It is also produced by the human body, and this is called endogenous galactose.