Foods have the ability to influence the post-workout recovery process (as well as, as will be seen later, body composition) regardless of their calorie content. This ability derives from some of the particular substances that constitute food, called nutrients or, more simply, nutrients.

Nutrients

  Nutrients, trivially, are all those substances that nourish the body, providing it on the one hand with the energy it needs to survive (calories) and on the other hand with the plastic material to build and reciprocate particular biological structures and to regulate certain vital functions. For our purposes, nutrients can be classified into two groups:

1. macronutrients: are those substances that provide calories;
2. micronutrients: these are those substances that do not provide calories.

Macronutrients consist mainly of:

1. carbohydrates (also called carbohydrates or sugars) and dietary fibre. Carbohydrates provide an average of 4kcal per gram;
2. fats (or lipids), which provide on average 9kcal per gram;
3. proteins (or proteins), which, like carbohydrates, provide 4kcal per gram.

Micronutrients, on the other hand, are:

1. vitamins;
2. minerals.

In addition to this, one must consider the very important water, which must be consumed in abundance every day. Of the two classes of nutrients, for the purposes of recovery and manipulation of body composition, it is the macronutrients that are most important. Therefore, macronutrients will be discussed in more detail than micronutrients (and water). Nevertheless, the diet, in order for one to remain healthy, will also have to include foods that contain the micronutrients. One cannot, therefore, completely neglect this class of nutrients, all the more so because some of them have an indirect influence on metabolism.

Metabolism

  We have encountered the term metabolism before. It can be considered as all those chemical reactions aimed at producing the energy the body needs. In this section we will explore the concept in more detail and highlight the link between this and nutrients for the athlete’s purposes. Metabolism can be classified into two different types:

1. aerobic metabolism;
2. anaerobic metabolism.

The latter, in turn, can be divided into:

1. alactacidic anaerobic metabolism;
2. lactacid anaerobic metabolism.

Aerobic metabolism requires the consumption of oxygen for energy production, whereas anaerobic metabolism does not. In lactacid anaerobic metabolism, in addition to energy production, lactate (or lactic acid) is also produced at the level of the muscle district being contracted. Finally, lactacid anaerobic does not involve the production of lactate, but that of a non-toxic but useless metabolite: creatinine.

Aerobic metabolism

  Let us now look in more detail at what each type of metabolism consists of. Aerobic metabolism is nothing more than a controlled combustion reaction in which the fuel is hydrogen and the comburent is oxygen. While the former is extracted from the surrounding air through lung respiration and transported to where it is needed via the blood, the latter comes from food. All macronutrients can serve as a source of hydrogen for aerobic metabolism. As for carbohydrates, during digestion they are broken down into the simplest sugar of all: glucose. This sugar is the only one that can circulate within the blood stream (the blood) and is the only sugar from which energy can be derived. It is found as such within the blood, while in muscle and liver cells it can be stored, to a certain extent, in the form of glycogen. In the context of aerobic metabolism, glucose, through a relatively complex sequence of chemical reactions called glycolysis, gives rise to the formation of pyruvate or pyruvic acid. From pyruvate, the body derives a second molecule, called acetyl-CoA (read acetyl-coenzyme A), which, through another sequence of chemical reactions called the Krebs cycle or citric acid cycle, is used to produce metabolic energy. If the body uses glycogen for energy production, it must first be broken down into glucose-6-phosphate, another sugar, through a process called glycogenolysis, which is then used to produce pyruvate in the same way that glucose is used for the same purpose. Finally, as far as fats are concerned, the lipids that are used to produce energy in the context of aerobic metabolism are called triacylglycerols or, more commonly, triglycerides. It is also possible to obtain acetyl-CoA from triglycerides through a series of chemical reactions called β-oxidation (read beta-oxidation), and also in this case acetyl-CoA is introduced into the Krebs cycle to produce energy. As for proteins, since they mainly have a plastic and transport role within the body, they are rarely used for energy production. More specifically, when the other two macronutrients are in short supply, they can be used in the liver as a precursor to produce glucose, which is then used as described above. The process by which glucose is obtained from proteins is called gluconeogenesis. In conclusion, therefore, to produce chemical energy through aerobic metabolism requires firstly air, from which to extract oxygen, and secondly carbohydrates, from which to extract glucose (or glucose-6-phosphate), or alternatively triglycerides. Only rarely does the body use proteins to produce energy through aerobic metabolism.

Lactacid anaerobic metabolism

  We have seen that aerobic metabolism consists of a controlledcombustion process. In the context of this process and, more specifically, in the Krebs cycle, hydrogen is ceded to progressively more affine acceptors until it reaches oxygen, activating combustion. The task of yielding hydrogen is entrusted to two molecules called nicotinamide-adenine dinucleotide and flavin-adenine dinucleotide, more commonly known as NAD and FAD respectively.  Now, when the energy demands of cells are very high, as the extraction of oxygen from the air and its transport to where it is required are relatively slow processes, there may be a shortage of these molecules. This implies an inability on the part of NAD and FAD to discharge the hydrogen they are carrying. This is where lactacid anaerobic metabolism comes into play: it consists of a single reaction whereby NAD and FAD, instead of letting the hydrogen enter the Krebs cycle, more rapidly discharge it onto the pyruvate produced by glycolysis. This reaction, called anaerobic glycolysis, involves the transformation of pyruvate into lactate (also called lactic acid) with the production of chemical energy. It is particularly important to emphasise that the pyruvate required for anaerobic lactacid metabolism is produced from glucose.

Anaerobic alactacidic metabolism

  Finally, alactacid anaerobic metabolism. It is heavily involved when energy demands exceed even the capacity for production by anaerobic glycolysis. It consists of a single chemical reaction, even faster than that involved in lactacid metabolism, between a molecule called phosphocreatine and another called adenosine diphosphate (ADP). The result is a creatine molecule and, of course, energy. Once the body has exhausted the need for such a large amount of energy, it re-phosphorises creatine (i.e. turns it back into phosphocreatine). This is done by means of aerobic metabolism, which is more active for the short time it takes for this operation to take place.

The energy efficiency of metabolism and its relationship to athletic activity

  We have seen that some forms of metabolism are faster than others in producing energy. More specifically, that lactacid anaerobic metabolism is faster than aerobic metabolism and that alactacid anaerobic metabolism is the fastest of all. The speed with which energy is produced, however, is not the only relevant aspect. The duration in efficiency is also important. It is maximum for aerobic metabolism (unlimited) and minimum for alactic anaerobic metabolism. Lactacid anaerobic metabolism, as far as this parameter is concerned, lies somewhere in between the other two. More specifically, it is possible to utilise the alactacid anaerobic metabolism for at most twenty seconds, the lactacid metabolism for at most a few minutes, and the utilisation of glycolysis in the context of aerobic metabolism for around twenty minutes. Now, it is clear that different training efforts require the use of different metabolisms. An athlete whose energy efficiency needs to be maintained for a long time will use mainly aerobic metabolism, whereas someone who needs a large amount of energy in a short time will use anaerobic mechanisms to a large extent. These needs must necessarily be taken into account when setting up a diet protocol. In fact, the shorter the time one has to produce energy, the greater the demand for glucose. It follows that endurance athletes, such as marathon runners, have a lower need for carbohydrates (glucose or other carbohydrates from which glucose can be obtained) in proportion to their total calories taken in than athletes whose performance is more intensive, such as middle-distance runners. Similarly, sedentary people have less of them than athletes. It is therefore necessary to analyse the energy requirements of the activity in detail, because the proportion of carbohydrates to fats must (also) be functional to it.

Plastic requirements

  Nutrition is not just about obtaining energy for metabolism. It also has the purpose of supplying the body with plastic material. Particularly important for this are certain types of fats, called unsaturated fats, and proteins, which are the primary constituents of muscle tissue (more on unsaturated fats later). As far as fats are concerned, the so-called essential fatty acids (EFAs) are well known in nutrition. These are particular fats that the body needs, but cannot produce itself from precursors. They must therefore necessarily be taken in through the diet. They are α-linolenic acid (alpha-linolenic acid) and linoleic acid. Their biological functions are varied, often performed indirectly as precursors of other fats. More specifically, the main fats obtained by processing the essentials are the two semi-essential eicosanoids eicosa-penta-enoic acid (EPA) and docosa-hexa-enoic acid (DHA), synthesised from α-linolenic acid, linolenic as well as arachidonic acid, also semi-essential, produced from linoleic acid. In terms of their nomenclature, eicosa-penta-enoic acid is also called thymnodonic acid, while docosa-hexa-enoic acid is also called cervonic acid. As they are semi-essential, although they can be produced from precursors, the amount of these fatty acids that can be synthesised endogenously will still be insufficient, so at least some of them must also be taken exogenously, as is the case with essential fats. Essential fats and their derivatives are involved in the regulation of inflammation and blood coagulation, in the metabolism of carbohydrates and fats, as well as in the regulation of blood pressure and the prevention of atheromas (i.e. life-threatening occlusions of arteries); they also form part of cell membranes (especially those of the nervous system) and have a transport function within the blood stream. As for proteins, the protein requirements of athletes are known to be higher than those of sedentary people because physical activity physiologically produces damage to the muscular structure, which requires new ‘raw material’ to be able to rebuild the damaged tissue. This need is even greater in the case of athletes who need to increase muscle mass, since the proteins needed to repair the damage caused by training must be supplemented by those needed to build up new tissue. These needs are also relevant and must be taken into account when designing a diet.