PROTEIN
Milk is recognised as an excellent source of high-quality protein. Cow’s milk contains about 3.3% protein (8 g in a typical 250 mL serving), of which 82% is casein and 18% is whey protein.
Milk protein is considered a ‘complete’ protein as it contain all the essential amino acids the body needs, and so contributes to all the classic functions of protein: anabolism (body building); synthesis of biological catalysts (to enhancing biological functions); plasma and membrane transport; structure and movement; molecular folding of protein chains; immune function; and growth and differentiation.
In addition, research shows that the bioactive peptides in dairy have unique functions, such as being involved in nutrient transport, immunomodulation, gastrointestinal function and flora support, cell signalling, and antimicrobial and antiviral activity.
Milk protein also has an important role in metabolic health given its effect on satiety and body composition, which indirectly aids weight management. 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.
Whey proteins, which make up about 20% of milk protein, are a group of globular proteins present in the fluid fraction when milk is separated into solid curds and liquid whey (e.g. in cheese making). These proteins are rich in branched-chain amino acids (leucine, isoleucine and valine) and are recognised for their role in muscle maintenance. Whey proteins are also referred to as ‘fast’ proteins, as they remain in a liquid state in the stomach and so increase amino acid availability and absorption. Because of the rapid availability of amino acids, whey protein is thought to have a role in satiety, thereby curbing excessive food intake and helping to prevent weight gain.
Caseins, which make up about 80% of milk protein, are a group of phosphoproteins and found mostly in the solid fraction when milk is separated into curds and whey (e.g. in cheese making). Caseins are referred to as ‘slow’ proteins as they clump together in the low pH conditions in the stomach, resulting in their amino acids being released into the bloodstream at a slower pace. Caseins have a high proportion of histidine, methionine and phenylalanine.
Casein proteins are an important nutritional component of cow’s milk as they transport nutrients such as calcium and phosphorus and support sustained increases in muscle synthesis and limits muscle breakdown.
Generally, all the energy and nutrients we need can be provided by a healthy, balanced diet. Therefore, supplements are usually required only when a specific deficiency is identified.
Athletes can fulfil high protein needs with protein-rich foods such as dairy products, meat, fish, eggs or soy. The intake of supplemental protein when the diet is already sufficient in protein is unlikely to pose any additional benefit. There is also little evidence to support the benefit of supplementing with individual amino acids when athletes are already consuming an adequate diet.
However, some athletes find it difficult to consume protein food sources at the ideal time and then a protein supplement may add some convenience. It is important to note though that protein supplements may contain extra or undeclared ingredients and impurities.