Amino acids have already been encountered in the course of discussion. It is quickly (and trivially) repeated here that they are the building blocks of proteins.

Function

Taking in a significant amount of amino acids in the context of a single meal establishes a state, usually physiological, called hyperammoniacidemia, i.e. an excess of amino acids in the blood. This circumstance (again, although physiological) gives rise to a reaction on the part of the organism whereby two mechanisms are activated to restore the blood state prior to intake. Well, one of these mechanisms is the incorporation of excess amino acids present in the blood into muscle cells (the second will be discussed later). This leads to an increase in their mass. A study by Biolo (1997) shows a 291% increase in muscle mass in bodybuilders who took branched-chain amino acids. In addition to this anabolic effect, amino acids also possess an anti-catabolic one: if they are taken together with carbohydrates during bodybuilding training, they have the ability to counteract the increase in blood levels of cortisol, which, as already discussed, can initiate muscle catabolism (Bird, 2006). As for the optimal profile that amino acid supplementation should have, Sugita (2001 and 2003) analysed the process of depletion of the body’s amino acid reserves to identify it. According to this author, a maximally effective product should only contain essential amino acids (which, we quickly remind you here, are those that the body cannot produce itself from precursors), glutamine, arginine and proline. Tipton (1999), also points out that essential amino acids have the power to enhance the anabolic function of proteins. Although amino acids are digested more quickly than proteins, they do not have to compete with the latter for absorption. Of these, the branched ones in particular have the power to trigger anabolic processes that would not take place without their supplementation (Karlsson, 2004). More specifically, leucine has the power to increase the sensitivity of muscle cells to the anabolic action of proteins. Taking leucine for this purpose is particularly important for those who are no longer very young, as the response of muscles to protein tends to decrease with age. Other anabolic functions of branched-chain amino acids are not known for sure, but it is assumed that they result in increased growth hormone secretion. Leucine can also reduce muscle catabolism by 62% when taken together with protein and carbohydrates. Glutamine could also be a potential GH stimulator. Finally, arginine also deserves special note, which acts via four different mechanisms:

1. acts as a stimulator of nitric oxide (NO), the levels of which are positively correlated with the accumulation and retention of muscle mass;
2. acts as a growth hormone stimulator, although this effect is somewhat controversial;
3. promotes endogenous creatine synthesis (see);
4. acts as a stimulator of IGF-1 (an anabolic hormone, which has already been encountered previously).

Regarding nitric oxide, in a resting muscle, when nitric oxide production is inhibited, protein synthesis also decreases (by 15%). Conversely, an increase in the former results in an increase in anabolism, although only very marginally. It would therefore appear that the effect of nitric oxide is more anti-catabolic than anabolic. Furthermore, following the application of a physical load, the hypertrophic response is halved if there is inhibition of nitric oxide production compared with normal conditions. And if the physical load is significant, nitric oxide participates in the activation of stem cells, which are responsible for repairing damaged muscle fibres. Finally, nitric oxide contributes to triggering the production of hepatocyte growth factor (HFG), which facilitates the transformation of stem cells into muscle fibres. However, these effects have not been confirmed in all studies. With regard to arginine’s effect on growth hormone, it should be made clear that while some studies (Isidori, 1981) demonstrate its effectiveness only in combination with lysine (another amino acid), there is a significant inter-individual sensitivity to supplementation. More specifically, a study by Moore (1998) shows that there are some individuals in whom GH secretion increases very significantly following arginine supplementation, others in whom the correlation between arginine intake and growth hormone secretion is more modest and, finally, some individuals who are completely insensitive to arginine (at least in relation to its role as a GH stimulator). I dare to speculate that this is due to the influence of arginine not only on GH, but also on insulin. Since the latter hormone is antagonistic to GH (the intake of arginine in the context of high-glycaemic-load meals should therefore be avoided), and since arginine stimulates the production of both, the effect on growth hormone may be predominant in some individuals, while in others the effect on insulin may be predominant. If this were the case, it would obviously be the former who would benefit more from arginine supplementation, while the latter might be the less sensitive individuals. Finally, with regard to the effect of arginine on IGF-1, a study by Hurson (1995) highlights the role that supplementation of this amino acid plays in increasing the production of this hormone, as well as in nitrogen retention (an essential component of proteins, the elimination of which is associated with muscle catabolism).

Negative notes

It has been said that one of the mechanisms the body uses to eliminate excess amino acids from the blood is their incorporation into muscles, with a consequent increase in muscle mass. This, however, is not the only way in which the restoration of the blood state prior to amino acid intake takes place: the second mechanism involves the disposal of amino acids by the liver, which therefore, at least in theory, may be overworked. One way to guide the body in choosing the mechanism to use to eliminate amino acids from the blood is to take them during the anabolic window (this was done in Biolo’s study mentioned above). There is evidence, however, that even in sedentary subjects there is an increase in muscle mass following amino acid intake, albeit to a lesser extent than in athletes (Biolo, 1997). A negative reading of this finding could be that the body, in any case, uses both the mechanism that favours the increase in muscle mass and that which can lead to hepatic fatigue to regulate ammonia. In other words, although by taking amino acids in the context of the anabolic window it is possible to shift the balance between the use of the two mechanisms towards the one functional to increasing muscle mass, the use of the other cannot be entirely prevented. To this possible adverse effect should be added those specific to arginine, discussed in the section on recovery supplements.

Form and dosage

Most amino acid supplements are commercially available in the form of tablets or powders to be dissolved in a drink. With regard to dosage, please refer to the specific discussions on branched-chain amino acids, arginine and glutamine in the section on recovery supplements.