Trivially, these are proteins in soluble form that can be added to drinks. There are several types, but the most relevant are whey protein (whey or serum protein), casein, egg protein and soy protein.
Function
It is now widely proven that, in the context of low-calorie diets, consuming a significant amount of protein (of course, as a percentage of the other macronutrients) helps to prevent the loss of muscle mass. Moreover, since protein constitutes the structure of muscles, increasing the amount of muscle tissue inevitably passes through an adequate protein intake. In order to promote the supply of new lean tissue, the most effective proteins are whey or serum proteins. A very important particularity of whey proteins is their ability to activate, more than other proteins, the stem cells in the muscles, i.e. those particular structures responsible for the affixation of new muscle tissue. Indeed, seroproteins have the potential to increase overall muscle anabolism by 68%. It should be noted, however, that this increase in the anabolic part of the metabolism does not translate into an equal increase in muscle mass, since, in any case, part of it is offset by the physiological process of catabolism, which seroproteins are unable to hinder except, perhaps, to a very small extent. Approximately 25% of serum proteins are made up of branched amino acids (see), especially leucine, with an average of almost 12%. Since they are also very rich in cysteine (another amino acid, contained in quantities of 2.45g per 100g of product), they also have an antioxidant effect. Unfortunately, they are relatively poor in arginine and glutamine (other amino acids). Of all proteins, these are the most rapidly absorbed, but in the context of serum proteins alone, it is possible to classify them according to how they are separated from milk, resulting in a different absorption rate. It is therefore possible to distinguish:
- concentrated proteins: of all, these are the slowest-absorbing;
- protein isolate: absorption rate is medium;
- hydrolysed proteins: absorption is very rapid.
It should be noted, however, that although there is indeed a difference in the rate of absorption of the various forms of seroproteins, it is not as marked as is sometimes advertised (Sindayikengera, 2006). Now, it has been made clear above that serum proteins mostly have an anabolic function and are not able to counteract the catabolism of muscle tissue. Instead, casein, another protein extracted from milk, is better suited to this purpose, following the intake of which muscle catabolism is reduced by 34% (by contrast, the anabolic effect is only 31%; less than half, therefore, that of seroproteins). Like serum protein, casein is also relatively low in arginine, but has significant levels of glutamic acid (another amino acid from which the body is able to synthesise glutamine). Exactly the opposite of serum protein, casein is among the proteins that take the longest time to be absorbed. This is because, in contact with the acid secretions of the stomach, it gives rise to a precipitated compound (Boirie, 1997), i.e. the solid part of the protein separates from the liquid in which it is dissolved. Like serum proteins, casein is also present in different forms: caseinate hydrolysate has a higher biological value than sodium caseinate, so the hydrolysed form is preferred over the other. Given the difference between serum protein and casein in speed of absorption and in relation to metabolic function, it is usually recommended to take serum protein in the context of the anabolic window and casein before fasting periods. More particularly, casein intake is recommended before the fasting period, which always takes place during the sleeping hours, i.e. before going to bed. Serum protein, in fact, constitutes readily available plastic material and it is a good idea to supply the body with it precisely when it is most likely to make use of it. The slow and constant absorption of casein, on the other hand, hinders the physiological catabolism that takes place particularly during periods of fasting. The above advice, therefore, remains valid in principle, but all too often ends up being a trivialisation of a problem that instead turns out to be more difficult to solve. In fact, in a study by Tipton (2001), the effectiveness of the anabolic function of protein consumed immediately before a short bodybuilding session (less than 45 minutes) exceeded that of supplementation at other times by 80%. The reason for this is that doing so ensures that you already have the necessary amount of protein in your blood stream to cover the increased requirements that will result from the upcoming loading unit. On the other hand, in the case of longer training sessions (the bibliographical data refer to a duration of more than 2 hours), it is recommended to take protein 10 to 15 minutes before the end. In this way, while protein will have an immediate effect in terms of reducing brain fatigue, thus allowing you to perform at your best in the final part of the session, the amino acids of which protein is composed will start to reach your muscles right at the end of the workout, maximising the anabolic response. Until now, only proteins originating from milk have been covered, but these are clearly unsuitable for individuals who are intolerant to them. For these athletes, good (and cheaper) alternatives to serum proteins are egg proteins, which are rich in sulphur amino acids and phenylalanine (another particular amino acid). The speed of absorption of egg protein is slower than that of serum protein, so, taken after training, it has less anabolic potential. Finally, soy protein could replace serum protein in the context of a vegan diet, but its absorption rate is, of all the alternatives analysed here, the lowest. To conclude, it should be pointed out that the anabolic and anticatabolic function of protein, while dependent on the type of training load one undergoes, is not limited to protein powder alone. It is possible to obtain this benefit even without taking protein powder, provided one observes a high-protein diet. On the other hand, protein powder could (and, in some circumstances, should) also be taken in the context of other types of diets, as an integral part of the diet.
Negative notes
Whey protein, egg protein and casein do not have any adverse effects (disregarding those of the widespread additives mixed with them, for which please refer to the appendix). The case of soya protein, on the other hand, is different: it contains substances called isoflavones, which have a well-known oestrogenic effect. A study by Dillingham (2005) shows that the testosterone level in male athletes drops by up to 10% when taking soya protein for 29 days. An intake of 57 days shows a steady increase in female hormone levels, which has a negative effect on strength performance. Muscle anabolism is also impaired. Once the intake is stopped, testosterone and oestrogen levels return to normal. In light of this, although sporadic consumption of soya or nutrients derived from it has no negative impact on either athletic performance or body composition, men interested in increasing strength and muscle mass should beware of regular consumption of these foods. For women, on the other hand, soya protein intake has no negative repercussions on either body composition or performance. On the contrary, these nutrients exert a peculiar anti-catabolic action, presumably because isoflavones, as substances with antioxidant action, preserve the structural integrity of muscles (Stroescu, 2001). Regardless of the oestrogenic effect of soy proteins, however, their anabolic potential in both male and female athletes is much less than their animal counterparts. This is partly due to their limited bioavailability: whereas the bioavailability of serum protein is around 92 per cent, that of soy protein is no more than 78 per cent. A study by Bos (2003) shows that 20% more protein is destroyed during digestion if the source is soya. It is also relevant that the difference between the anabolic potential of serum protein and that of soy protein increases as the protein intake in the diet increases and as the period of administration increases (Brown, 2004). The latter point is not surprising, as female hormone levels tend to rise steadily and progressively over time. A study by Phillips (2005) shows a partial loss of anabolic potential after 12 weeks of administration, at the end of which time, athletes begin to experience difficulties in increasing strength and muscle mass. Evidently, the inclusion of soy protein in a relatively low-protein diet, which is not too long in duration (quantifying precisely is impossible for me here), is a relatively better solution than opting for the introduction of soy-based protein supplements in a high-protein, time-consuming diet. Milk-derived proteins, however, prove to be the ideal solution wherever possible.
Form and dosage
Soluble proteins are available on the market in the form of a powder to be dissolved in a drink (usually water or milk). Many commercially available products mix in various proportions serum proteins of different extracts and sometimes casein (or other protides). The idea is not a bad one, since even in the context of the muscle anabolic window fast-absorbing proteins with others that are absorbed slowly have proved to be a winning strategy for muscle mass management. The amount to be taken depends on the diet you are following and your requirements. Naturally, as these are macronutrients, it is necessary to ensure that the soluble proteins taken are included in the diet so that the set parameters of calories to be consumed and macronutrient balance are met. In this regard, protein powder can be particularly useful, on the one hand for ‘balancing’ calories and proportions between macronutrients in the context of a low-calorie diet (in fact, with just a few foods it is possible to create very small portions, suitable for low-calorie contexts), and on the other hand for having greater control over the speed of absorption and, therefore, replenishment of the body’s available supplies.