Breast milk is the only food able to provide all the nutrients needed to satisfy the nutritional needs of the newborn. After this period, cow's milk replaces the maternal milk, becoming a very important food - but not complete - even for the body of children, adults and the elderly.
The nutritional importance of cow's milk derives from its excellent content in proteins, essential amino acids, calcium, phosphorus and vitamins B1, B2 and A (contained above all in whole milk).
Milk and protein
The proteins 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 is more abundant in human milk, while beta-lactoglobulins prevail in the vaccine). It is therefore not allergic to the 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 an intolerance towards this food (generally due to a deficiency of the enzyme lactase). See the following: Food allergies
Casein
Along with fats 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 milks) and to artificially separate the other components of cow's milk.
Although not particularly water-soluble, casein micelles are kept dispersed in milk. However it is possible to make them aggregate (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 makes it possible to obtain separately a colloidal aggregate, containing the caseins, and a solution, called whey, containing water, lactose, lactoglobulins and lactalbumin ( whey protein ). The same result, as previously mentioned, can be obtained using a proteolytic enzyme (such as rennina del presame) or working all in an acid environment (a little like in our stomach).
There are several 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.
The serum also contains immunoglobulins, which derive directly from the animal's blood plasma and play an important immune function. Whey proteins also include a long list of enzymes, protein hormones and growth factors.
Milk protein supplements
Lactoglubulins contain easily digestible oligopeptides by the body. In fact, this type of protein contains bipeptides or tripeptides that can be absorbed as such without undergoing digestive processes.
Just like with the glycemic index of carbohydrates, proteins can also be classified as "slow and fast".
Whey proteins are in the class of fast proteins as they are highly digestible and very fast entering the circulation. Caseins, due to a more complex chemical structure, are instead gradual release (slow) proteins with marked anticatabolic properties.
These considerations derive from a study that measured blood levels of leucine in two groups of healthy subjects who, after a 10-hour fast, took 30 grams of whey protein and 30 grams of casein, respectively. The results gave way to the trade of numerous supplements based on slow, fast, "partially digested" or mixed proteins.
Currently the major experts in the field of protein supplementation recommend taking whey protein in the morning or in post-workout. The use of caseins would instead be indicated at other times of the day and especially before going to bed to avoid nocturnal catabolism.
These recommendations refer to the results of the study mentioned above but it is very important to consider also other important aspects:
- in the study, the subjects had been fasted for ten hours, while most individuals who take milk protein supplements consume at least 4 meals throughout the day. The presence of residual food in the stomach that is not yet completely digested influences the digestion of protein supplements. An even more important role is played by the other nutrients with which these supplements are combined. The association with fibers, fats, or other proteins slows down the digestion of milk proteins.
- By taking whey protein together with a glass of whole or partially 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 the amino acids deriving from protein digestion is theoretically facilitated (thanks to the greater insulin response).
- To promote the optimal digestion and absorption of milk proteins it is important to avoid taking them together with meat, fish, legumes or over-processed meals.
- The ideal protein supplement does not exist as it varies according to specific individual needs, the sport practiced and the training period. For example, athletes who practice resistance disciplines need proteins rich in branched amino acids (BCAAs) 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 produced using ion exchange or ultrafiltered proteins.
- Milk proteins isolated by ion exchange have a higher cost and higher protein percentage; the reduced fat and lactose content makes them more digestible and better tolerated.
- Microfiltered whey proteins can have a variable protein content from 80 to 90%. In the first case the lipid content (5%) and glucidic (5%) is clearly higher.
See also: How much protein in a balanced diet?
