Function: Maintain, grow and repair, muscle tissue, nails, hair, enzymes and antibodies. There are 9 essential amino acids and 12 non essential amino acids. We can produce these non esseential amino acids through our body processes but we can't produce the essential amino acids so we gain them by our diet.
Sources: There are two types of protein, High biological value and low biological value(LBV). High biological value(HBV) proteins contain all of the essential amino acids whereas low biological value proteins do not contain all amino acids required. HBV proteins are usually found in animal products such as meat, dairy, poultry and soya beans(the only vegan HBV protein). LBV proteins are usually found in plant products in chickpeas, beans, mycoprotein(mushroom fungus and eggwhite(or potato starch)), Tofu(curdled soya milk), TVP(Textured vegetable protein made from soya beans and flour). Different LBV proteins can be mixed to gain all essential amino acids and this is called protein complementation.
Daily Requirement: 55g of protein is required for men and 45g of protein is required for women. Pregnant women require 6g more protein, growing children need more protein(relative to size and mass) and physically active people need more protein for muscle growth and repair.
Excess of protein: Extreme liver and kidney stress as they help process these proteins.
Deficiency: This can cause slowed growth in places such as hair, nails and skin and can cause wounds not to heal fast. The immune system does not function properly as well so there is a higher risk of infection. If this becomes a severe malnutrition, you can develop kwashiokor or odema(build up of fluid in feet or in severe cases, swelled up bellies).