Breast milk is the only food capable of providing all the nutrients necessary to meet the nutritional needs of the newborn on its own. After this period, cow's milk replaces mother's milk, becoming a very important - but not complete - food also for the organism of children, adults and the elderly.
The nutritional importance of cow's milk derives from its excellent content in protein, essential amino acids, calcium, phosphorus and vitamins B1, B2 and A (mainly contained in whole milk).
Milk and Proteins
The protein content of cow's milk is characterized by different types of proteins. The most abundant, you call casein (from the Latin caseus "cheese"), they make up 80% of the protein fraction and have an amino acid composition ideal for growth and development. The remaining 20% is made up of different types of proteins (beta-lactoglobulins and alpha-lactoalbumins) which are grouped under the common name of "whey protein".
The proteins present in cow's milk are responsible for some of the most common food allergies. The typical allergic manifestations are mainly caused by beta-lactoglobulins and to a lesser extent by caseins (alpha-lactalbumin are more abundant in human milk, while beta-lactoglobulins prevail in cow's milk). You are therefore not allergic to milk itself but only to one or more proteins contained in it. It is important not to confuse milk allergy (whose main symptoms are often severe) with intolerance towards this food (generally due to a deficiency of the lactase enzyme).
See by the way: Food allergies
Along with fat and lactose, caseins are one of the main organic components of milk.
Caseins are composed of different types of proteins bound together with water, enzymes and mineral salts (mainly calcium and phosphorus) in the form of spherical aggregates called micelles. The micellar structure of casein is very important for digestive processes, for the food industry (production of cheese and fermented milk) and for artificially separating the other components of cow's milk.
Although not particularly water-soluble, casein micelles are kept in dispersion in milk. However, it is possible to make them aggregate together (coagulate) by enzymatic action or by acidification, but not by heating. The result of this coagulation is a gelatinous material, which takes the name of rennet and represents the first phase of cheese preparation.
Lactalbumin and Lactoglobulins
The high-speed centrifugation of skimmed milk allows to obtain separately a colloidal aggregate, containing caseins, and a solution, called whey, containing water, lactose, lactoglobulins and lactalbumin (whey protein). The same result, as previously mentioned, can be obtained by using a proteolytic enzyme (such as rennin from rennet) or by working everything in an acidic environment (a bit like it happens in our stomach).
There are various whey proteins in milk. The best known are lactoalbumin and lactoglobulins, which represent an exceptional source of branched amino acids. Compared to caseins, they have a more complete amino acid profile, which gives them a biological value even higher than that of egg proteins.
In the serum there are also immunoglobulins, which derive directly from the blood plasma of the animal and perform an important immune function. Whey protein also includes a long list of enzymes, protein hormones, and growth factors.
Milk Protein Supplements
Lactoglubulins contain oligopeptides that are easily digested by the body. This type of protein in fact contains bipeptides or tripeptides that can be absorbed as such without undergoing digestive processes.
Much like the glycemic index of carbohydrates, proteins can also be classified into "slow and fast".
Whey proteins fall into the class of fast proteins as they are highly digestible and very fast in entering the circulation. Caseins, due to a more complex chemical structure, are instead gradual (slow) release proteins with marked anti-catabolic properties.
These considerations derive from a study that measured blood levels of leucine in two groups of healthy subjects who, after fasting for 10 hours, had eaten 30 grams of whey protein and 30 grams of casein, respectively. The results have triggered the commercialization of a number of slow, fast, fast "partially digested" or blended protein supplements.
Currently, the leading experts in the field of protein supplementation recommend taking whey protein in the morning or post-workout. The use of casein would instead be indicated at other times of the day and especially before going to bed to avoid catabolism at night.
These tips are based on the results of the aforementioned study but it is very important to also consider other important aspects:
- in the study, the subjects had been fasted for ten hours while most of the individuals taking milk protein supplements consume at least 4 meals throughout the day. The presence in the stomach of residual food that has not yet been fully digested affects the digestion of protein supplements. An even more important role is played by the other nutrients with which these supplements are combined. In fact, the association with fibers, fats, or other proteins slows down the digestion of milk proteins.
- By taking whey proteins together with a glass of whole or semi-skimmed milk it is possible to slow down the digestive process by mimicking the action of caseins. If the same supplement is combined with simple sugars, the entry into the cells of amino acids deriving from protein digestion is theoretically facilitated (thanks to the greater insulin response).
- To promote optimal digestion and absorption of milk proteins, it is important to avoid taking them together with meat, fish, legumes or overly elaborate meals.
- The ideal protein supplement does not exist as it varies in relation to specific individual needs, the sport practiced and the training period. For example, athletes who practice endurance disciplines need proteins rich in branched chain amino acids (BCAAs) in order to counteract the muscle catabolism induced by long-lasting activity.
- The essential amino acid content of casein is not much lower than that of whey proteins. The abundance of glutamine and the overall anticatabolic effects make caseins a valid and cheaper alternative to whey proteins.
- The best whey protein supplements are made using ion exchange or ultrafiltered proteins.
- Milk proteins isolated by ion exchange have a higher cost and a higher protein percentage; the reduced fat and lactose content makes them more digestible and better tolerated.
- Microfiltered whey proteins can have a protein content ranging from 80 to 90%. In the first case, the lipid (5%) and carbohydrate (5%) content is significantly higher.
- How Much Protein in a Balanced Diet?
- Excess protein in the diet
- Foods richer in protein
- Branched chain amino acids
- Hyperprotein diet
- Amino Acid Supplements