Milk is recognised as an excellent source of high quality protein. Cow’s milk contains about 3.25% protein (7 g in a typical 200 ml serving), of which 82% is casein and 18% is whey protein.
Milk protein has numerous roles in human nutrition. All classical functions of proteins – anabolism, biological catalysts, plasma and membrane transport, movement, structure, protein folding, immunity, growth and differentiation – also apply to dairy protein, mainly through the provision of amino acids for protein turnover. The bioactive peptides of dairy have recently been shown to have unique functions, including involvement in nutrient transport, immunomodulation, gastrointestinal function and flora, cell signalling and antimicrobial and antiviral activity. In addition, milk protein plays an important role in metabolic health. Dairy protein may indirectly aid weight management through its effect on satiety and body composition. It seems to function synergistically with physical activity and is a popular recovery drink after exercise. Bone health is also related to dairy protein intakes. The protein in milk is considered a ‘complete’ protein as it contains all of the essential amino acids (building blocks) used during growth and repair.
Whey proteins are a collection of globular proteins present in whey (whey is produced when milk is separated into solid curds and liquid whey e.g. in cheese making). Milk protein consists of 20 % whey proteins, which are rich in branched chain amino acids (leucine, iso-leucine and valine) recognised for its’ role in muscle maintenance.
Caseins are a collection of phosphoproteins and it is the most abundant protein in cow’s milk, making up 80 % of the protein fraction. It has a higher proportion of histidine, methionine and phenylalanine. It is an important component of cow’s milk as it transports nutrients such as calcium and phosphorus.
Generally, all of the energy and nutrients we need can be provided by a healthy, balanced diet – with no need for supplement use unless a deficiency is identified. Athletes with a high protein need can fulfil the need with protein-rich food sources such as dairy products, meat, fish, eggs and soy. The intake of supplemental protein when the diet is already sufficient in protein will probably pose no additional benefit for the athlete. There is also little evidence to support the benefit of supplementing with individual amino acids when athletes are consuming an adequate diet. Some athletes although find it difficult to consume protein food sources at the ideal time and a protein supplement may add some convenience. Athletes should although be aware of protein supplements that contain extra ingredients and impurities.