Protein is one of the three macronutrients, the main components of food from which we get energy (the other two are fat and carbohydrate). In chemical terms, ‘proteins’ are a class of millions of different molecules which make up much of the physical structure of animal bodies and perform most complex biological tasks. However, from the point of view of nutrition, these are almost all broken down by the digestive system and can be constructed as needed from the resulting components. These components are the amino acids.