6. Nutrition in sports
In the science of sports nutrition, an enormous amount of experience has been accumulated over time; however, its characteristics are so varied and individualized, that it is not possible to give a detailed overview of this subject in this work. So we will confine ourselves to a discussion of some topics a knowledge of which will lay the foundations for an understanding of the field of sports nutrition.
Nutrition is an exceptionally important determinant of sports performance, because it helps the organism during preparation, competition, and in the regeneration phase. In the period prior to physical load (training, competition) it plays a role in filling the energy reserves and fluid compartments of the body to an optimal level, while during loading it concentrates on the appropriate fluid- and energy intake (Radák 2016), and in the regeneration phase it is important when replenishing reserves, building up elements of the body (muscles, bones, joint elements, blood components, enzymes, etc.), and recovering from molecular and tissue level injuries.
In the field of sports nutrition, three areas have outstanding importance: The specification of the optimal concentration and qualitative components of
the two principal fuels of oxidation (fat and carbohydrates),
the building material (proteins), and
the materials necessary for the proper functioning of the body, such as water, ions and vitamins.
6.1. The role of carbohydrates in sports nutrition
Carbohydrates (CHO) have received particular attention among the oxidable nutrients taken up before, during and after sports activity, because, besides their role in building up glycogen stores, these can easily be taken up and quickly utilized even during physical loading. This group of organic macromolecules plays a significant role both in sports of an aerobic and an anaerobic character, because, in an appropriate quantity, it is capable of extending the limits of fatigue, and thus of performance. In the case of the low intensity, aerobic sports activity, the carbohydrate taken up prior to loading helps refill the glycogen reserves which – even though fatty acid utilization occurs at an ever increasing level during exercise or competition –, in terms of their absolute quantity, bear a significant load (i.e. they run down). During anaerobic activity, the well-replenished stores of glycogen and the increased blood sugar level provide the fuel for increasing carbohydrate oxidation. In terms of different training durations and intensities, the quantitative and qualitative parameters of CHO uptake are also different and personalized. In this, the type of carbohydrate and the CHO absorption capacity of the gut, for example, also play important roles, since taking up a too large quantity of carbohydrates of similar absorption type can cause problems for the digestive system (see for example Jeukendrup 2014).
The replenishment of glycogen stores is of high priority if activities are carried out repeatedly over a long period, e.g. during football championships, when athletes who play often have to perform at a high level again within a short time (Radák 2016). Glycogen synthesis occurs at the highest rate in the first hour following load, because the glucose uptake, heightened by muscle contraction, is intense even in the absence of insulin (Jentjens, Jeukendrup 2003; Moore 2015). Therefore, the consumption of 1–1.2 g/body mass kilogram (g/kg) carbohydrates in each hour of the 4-6 hour post-exercise period is recommended (Jentjens, Jeukendrup 2003; Moore 2015), or alternatively, an intake of a combination of 0.8 g/kg CHO and proteins, because this – due to the rise in the insulin level because of the presence of proteins – has the same effect on glycogen synthesis as does a higher value of CHO ingestion (1.2 g/kg), while it also increases the synthesis of muscle proteins (Jentjens, Jeukendrup 2003).
Those athletes who have a relatively long period of time (8–24 h) to regenerate between training sessions do not have to pay so much attention to the immediate CHO ingestion after exercising, since the refill of glycogen stores is less sensitive to timing than that of proteins (see below), provided that the required amount is available (Parkin et al. 1997, Moore 2015).
It is, nevertheless, important to emphasize that research on the issue of the carbohydrate consumption of athletes mainly involves young, trained athletes, who most of the time do not have weight problems. However, if one tries to relate the results to overweight or older people, the situation is totally different. Since a great deal of both everyday and sports experience supports the idea that a significant body weight reduction can be achieved by a CHO-poor diet, the question arises of whether this sort of diet may be adopted by those who struggle with overweight but do sports, or whether they should follow the general sports nutritional habits of a continuous and high level of CHO replenishment.
As a reference, the diet followed by athletes during a weight loss period can be used. In the weight loss period, an energy-reduced diet is coupled with a reduction in the quantity of CHO and an increase in the quantity of protein, which reduces the fat/lean mass ratio in the body (Phillips, van Loon 2011). Furthermore, it has been shown that physiological adaptations which are general to endurance sports (increased mitochondrial density, mitochondrial activity and lipid oxidation), have been induced by a reduced CHO intake in the same way as by a high intake (Bartlett et al. 2014, Moore 2015); therefore it is recommended to combine low and high CHO intake periods during the preparatory phase, boosting the glycogen stores by a high intake before competition (Bartlett et al. 2014). On the basis of these points, it seems that a CHO-poor diet coupled with a high protein intake, adopted to achieve weight loss, satisfies the energy demands posed by sports, and is also effective in terms of weight loss. Regarding the degree of CHO reduction, it is worth intensifying it to the point at which it does not cause an impairment in performance (Phillips, van Loon 2011).
6.2. The role of fats in sports nutrition
The availability of fatty acids in the body is important during sports activity, because a significant degree of fatty acid oxidation occurs during loading, hence it seemed reasonable to test the various aspects of fat-rich alimentation on athletes (Kiens, Hawley 2011).
It has been shown that a meal with a high fat content ingested before exercise decreases the utilization of carbohydrates during loading, but has no influence on performance (Hargreaves et al. 2004; Kiens, Hawley 2011; Burke 2015). Fat consumption during training does not bring success either, and what is more, above a certain amount it has also been shown to cause gastrointestinal complaints in athletes (Kiens, Hawley 2011).
As an effect of a permanently high fat content diet the extent of fatty acid oxidation increases, while that of carbohydrates decreases. As a result, the insulin resistance of the liver increases, and its degree of glycogen synthesis and glucose release capacity both decrease. Therefore, in the case of high intensity training, this is a diet to avoid, but it also has to be dealt with carefully among those doing other types of exercises (Kiens, Hawley 2011).
In the light of all this it can be stated that for sports, a diet rich in fat is not recommended (Kiens, Hawley 2011).
6.3. The role of proteins in sports nutrition
In the normal population, the consumption of a daily 0.72–0.8 g/kg of proteins is indicated as the amount which ensures the daily nitrogen balance (Moore et al. 2014, 2015). This need for protein intake is higher in older (~71 years) than in younger (~22 years) people (1.2 vs 0.72 g/kg; Moore et al. 2015). The daily amount is higher in athletes doing training, since the musculature and the body have an increased amino acid need due to the demolition-and-rebuilding cycles of certain proteins, so to maintain the equilibrium, more protein is needed. The exact value of this need has been assessed differently by different authors (1 g/kg/day [in endurance sports], Tarnopolsky 2004; 1.2–1.7 g/kg/day, Moore 2015; 1.3–1.8 g/kg/day, Phillips, van Loon 2011; a maximum of 1.6 g/kg/day even in top athletes [in endurance sports], Tarnopolsky 2004). In order to ensure a general development which produces the characteristic muscle proportions of a given sport or of a given individual, as well as in sports involving muscle building (body building), the protein balance has to be positive. It seems that after a high intensity (anaerobic) workout, 20 g of protein (in people weighing cca. 80 kg, i.e. roughly 0.25 g/kg per portion) of high biological value (whey, egg) sufficiently covers the amino acid required for the synthesis of muscle proteins in young athletes (Moore et al. 2009, Witard et al. 2014, Moore 2015). Any amount above this, ingested at once, will be oxidized, so it will not be built into the muscles (Moore et al. 2009, Witard et al. 2014). In older people (60-70 years old), however, a much greater amount (~0.4 g/kg/dose) than this is needed to be effective (Churchward-Venne et al. 2016). After exercise, the breakdown and the resynthesis of proteins start in the muscles, so the consumption of a small amount (30g) of CHO – because of its effect of increasing the insulin level – minimizes the breakdown of muscle proteins: thus, athletes are recommended to use a combination of carbohydrates and proteins, especially if they do multiple workouts in one day (Moore et al. 2014, Moore 2015). Data like these are not available regarding aerobic, endurance training, but similar amounts can probably be recommended as for anaerobic loading (Moore 2015).
The timing of protein consumption is also a very important factor: intake immediately following a workout maximizes protein synthesis in the muscles, and even a delay of three hours significantly decreases it (Moore 2015). The repeated intake of 20 g of protein every three-four hours (80 g in total) further increases the efficiency of protein synthesis, and it seems that it is advisable to keep the amount at 20 g, because neither 8 × 10 g doses, nor 2 × 40 g doses produce the same effect as the consumption of the 4 × 20 g doses; pre-sleep protein ingestion also contributes to the enhancement of efficiency (Moore et al. 2014, Moore 2015).
Similar results have been obtained by studying the strength training of older (~74 years) people: dietary protein (10 g protein, 7 g CHO, 3 g fat) ingested immediately after exercise augmented muscle hypertrophy, while the same protein consumed with a delay of two hours did not (Esmarck et al. 2001).
Of course, the composition of the protein is also important, since there are huge qualitative and structural differences between dietary proteins, so their amino acid profiles differ, as well as their digestibility and their rate of absorption. Maximal muscle protein synthesis is induced by the consumption of whey, more than by soy or milk casein protein (Moore et al. 2014, Witard et al. 2014, Moore 2015), but vegetal proteins, protein blends and – if the order of workouts and meals can be properly scheduled – of course, whole foods containing proteins can also produce an adequate amino acid profile to achieve this effect (Symons et al. 2009, Moore 2015). The simple ingestion of branched-chain amino acids (BCAAs) following resistance training also increases the synthesis of skeletal muscle proteins (Jackman et al. 2017).
Carrying out studies into the upper limits of the daily consumption of proteins is both risky and ethically objectionable, so the relevant values have not been established. Unfortunately however, several people overdo protein consumption on their own initiative. According to nephrological experience, individuals consuming too much protein stand a good chance of developing renal insufficiency, which is a serious condition requiring dialysis.
6.4. The role of water, ions and other substances in sports nutrition
The water content of the body is also a critical factor, especially during prolonged (aerobic) activity, and/or activity carried out in extreme heat, because water, which is lost through sweating owing to the cooling required following heat production, leaves the body at a rate proportionate to the time spent on the activity. In a state of water-deficit, muscles fatigue sooner (Montain et al. 1998). If the replacement of water is not adequate, body temperature can jump too high (hyperthermia), because, due to the shortage of water, the organism draws the blood in the inner vessels from the skin in order to maintain a level (although a reduced level) of the stroke volume: in this case, however, the efficiency of heat loss diminishes (Nadel et al. 1980). The water quantity also has to be accommodated to the CHO intake, because carbohydrates taken up in high concentrations inhibit water absorption (Jeukendrup 2014).
Vitamins and many important chemical elements (for example iron, magnesium, zinc, calcium, etc.) also influence physical and psychological performance. In this field, nevertheless, it is hard to formulate any precise and clear guidelines. Regarding vitamins and trace elements, for example, it is mainly known what the minimally required levels are, below which deficiency diseases may develop. Concerning the upper limits of what can be safely taken, there are only recommendations, because the exact data are missing. The cause of this, on the one hand, is probably that there are marked inter- and intra-individual variations in the needs of different individuals, as a function of diverse internal and external factors (e.g. Baker, Jeukendrup 2014), and on the other hand, that, compared to the minimally desirable level, the body also “tolerates” high concentrations without any symptoms. Thus, personal experimentation and experience matter a lot in establishing the right quantities, as do the false beliefs and information gained from hearsay which is believed uncritically. According to certain opinions, however, exaggerated calculations and over-consumption of vitamins are superfluous, since a balanced diet generally contains the required substances; it is better to pay attention to the body: it is best to consume what it desires, after having made sure that it is not harmful – keeping in mind that our diet should be made up of the most natural food possible.
The antioxidant vitamins (vitamin C, vitamin E) play an important role in neutralizing the effect of free radicals, but by taking them externally we may simply prevent the proper functioning of our natural antioxidant signal transduction pathways, which are activated as a result of free radicals: thus, the administration of antioxidants can significantly reduce training adaptation and the beneficial effects of sport (Gomez-Cabrera et al. 2008; Morales-Alamo, Calbet 2014); it also impairs, for example, the parameters of blood flow in the body (Trinity et al. 2016).
However, before any events which may involve significant oxidative stress because the individual has to produce an extremely high power output – for example a more serious competition –, supplementary antioxidants may help the body’s natural antioxidant activity (Gomez-Cabrera et al. 2008). Likewise, in the case of ageing or disease, the negative effect of the heightened oxidative stress exerted on the blood flow parameters can be mitigated by exogenous antioxidants during physical activity (Trinity et al 2016). Thus, a constant and exaggerated consumption of vitamin supplements, when not in harmony with physiological needs, is unfortunate, especially if we do not even know for certain the actual state and needs of our body.
6.5. Diet in sports with weight categories: the question of weight loss
In sports with weight categories, in the preparatory phase, athletes generally weigh more than they do during competition; therefore, they come through a period of weight loss before the contest. During this period, the consumption of carbohydrates is tightly restricted, which generally leads to successful weight loss, but in extreme cases, fluid replenishment may also be decreased in order to reach the desired competition weight, something which is not really an advantage in terms of performance. It is advisable to leave enough time for weight loss, since a too rapid weight loss leads to undesired consequences in terms of the immune functions, the physical and psychological functioning of the nervous system, and also of other factors.
Neither is it a negligible point that in competitive events in certain sports (e.g. judo, Brazilian jiu-jitsu), the weigh-in happens either immediately, or some hours, before the fight, or in other sports (wrestling, boxing) on the day before competition, so in the case of the latter sports, there is some time to regain weight (to at least partially restore the fluid compartments and the glycogen level); however, this is generally not sufficient for restoring the optimal physiological state (Radák 2016). It must also be noted that during competitions which extend over several days, due to the different weight tactics employed, by the last day some competitors may have already regained a significant weight, so that at the end of the competition, large body weight differences may develop, even between competitors fighting in the same weight category.
Nevertheless, to avoid too much weight loss, it is important that athletes start to restrict their weight gain during the preparatory phases, especially by paying attention to diet.