Functions of protein
- Growth, especially in children and pregnant women.
- Repair of body tissues after illness or injury, and maintenance of the body.
- A secondary source of energy: 1 g of protein provides 4 kcal.
Protein quality
- Proteins are made of amino acids. Essential (indispensable) amino acids can't be made by the body, so they must come from food.
- High biological value (HBV) proteins contain all the essential amino acids: meat, fish, eggs, milk, soya and quinoa.
- Low biological value (LBV) proteins lack one or more essential amino acids: most plant foods, such as beans, lentils, nuts, grains and seeds.
- Protein complementation: eating two LBV proteins together gives all the essential amino acids, such as beans on toast or hummus with pitta bread.
Too little or too much
- Deficiency: poor growth in children, poor healing, muscle wasting, and kwashiorkor (in severe cases, mostly in developing countries, causing a swollen belly and oedema).
- Excess: extra protein is used for energy or stored as fat, and can strain the liver and kidneys.
Alternative proteins
- Vegetarians and vegans can use tofu (from soya), textured vegetable protein (TVP), mycoprotein (Quorn) and tempeh.
Key terms
- Amino acids
- The building blocks of protein.
- Essential amino acids
- Amino acids the body can't make, so they must come from food.
- HBV protein
- High biological value protein, containing all the essential amino acids.
- LBV protein
- Low biological value protein, missing one or more essential amino acids.
- Protein complementation
- Combining LBV proteins to get all the essential amino acids.
- Kwashiorkor
- A serious protein deficiency disease in children.
- Mycoprotein
- A protein made from fungi, sold as Quorn.