Milk has a protein content of about 3.5%. Some dairy products contain more protein: for instance, dairy cheese spread contains on average over 11 g protein per 100 g and cheddar cheese an average of 25 g per 100 g. Protein contributes to the maintenance of normal bones and the growth and maintenance of muscle mass.
The protein in milk consist of 80% casein and 20% whey protein. Casein is also referred to as the ‘slow protein’ and whey as the ‘fast protein’. This is because the amino acids in whey generally peak more rapidly in the blood within the first two hours after consumption, whereas the amino acids in casein appear over a longer period of around six hours resulting in a lower peak value. (1,2) The protein content varies between milk, yoghurt, cheese spread and hard cheese (3).
TABLE 1 Nutrient Composition of milk and milk products per 100 g
Protein in milk and milk products
Proteins consist of chains of amino acids which are classified as essential amino acids (n=9) and non-essential amino acids (n=11). The body cannot synthesise the essential amino acids itself and therefore these need to be obtained through food. The essential amino acids are: phenylalanine, histidine, isoleucine, leucine, lysine, methionine, threonine, tryptophan and valine. Milk protein has a high digestibility and contains all nine essential amino acids in a greater amount than the reference value for protein.
- Lacroix, M. et al (2006). Compared with casein or total milk protein, digestion of milk-soluble proteins is too rapid to sustain the anabolic postprandial amino acid requirement. American Journal of Clinical Nutrition. 2006;84,1070–1079.
- Penning, B. et al (2011). Whey protein stimulates postprandial muscle protein accretion more effectively than do casein and casein hydrolysate in older men. American Journal of Clinical Nutrition. 2011;93,997-1005.
- McCance and Widdowson’s The Composition of Foods, Seventh summary edition. Cambridge: Royal Society of Chemistry.