The biochemistry of sports nutrition teaches us that carbohydrates are needed in sports
Interest in the study of the relationship between nutrition and physical performance (both in sports and work) has its roots in antiquity and remains highly relevant today. Research on this topic is very intense, also due to its economic impact. At the same time, there are behaviors by athletes and coaches that are neither rational nor scientific, which end up harming athletes and/or failing to achieve the desired results. In fact, some see the use of certain nutrients or foods as a way to induce greater muscle tissue formation, others see it as a method to increase athletic performance, and too few see it for what it is: a way to nourish muscle tissue that must cope with very different situations depending on the intensity and duration of the effort, according to the characteristics of the individual sport discipline.
If it is true that without adequate nutrient supplies, performance will undoubtedly be below the athlete's potential, it is equally true that excess nutrients do not contribute to better performance than what can be achieved with the correct amounts. Certain types of diets proposed for athletes can, in fact, cause serious damage to the body's homeostatic system and lead to lower performance, just as a nutritional deficit would.
Energy substrates consumed during physical activity
The consumption of energy (ATP) is fundamental for the muscle to develop its mechanical work. The energy substrates consumed during muscle activity depend on two fundamental variables: the duration and intensity of the effort. There are two ways to regenerate the ATP necessary for muscle metabolism: aerobic metabolism and anaerobic metabolism. In fact, the maximum effort that, theoretically, can be sustained by the muscle is related to the speed of ATP production.
Anaerobiosis ATP can be regenerated from phosphocreatine in an anaerobic manner (that is, without oxygen). The muscle loads up on phosphocreatine during rest and can use this energy reserve to develop, for a few seconds, considerable power. Once the phosphocreatine stores are depleted, ATP regeneration must occur by consuming energy substrates (carbohydrates, lipids, and proteins). Carbohydrates, unlike fats, can be used both aerobically (i.e., in the presence of oxygen) and anaerobically. The anaerobic process is less efficient but much faster, requires less energy, and remains independent of oxygen supply, which is a limiting factor.
Aerobiosis Muscle contains relatively high amounts of glycogen (glucose reserve). This molecule can be broken down both anaerobically and aerobically, resulting in lower power. ATP can also be formed from the oxidation of fats at a maximum rate similar to that of sugars. Whatever the energy source, aerobic metabolism develops less power, but is available for much longer duration efforts.
In general, it can be said that at low levels of activity, fat (lipid) consumption prevails, while at higher activity levels, anaerobic breakdown of glycogen occurs, and at even higher levels, phosphocreatine consumption. For moderate effort, the consumption of energy substrates varies over time: while in the short term glycogen breakdown prevails, this decreases proportionally over longer periods, during which fatty acid catabolism prevails. Moreover, glycogen consumption is not linearly proportional to workload.
Carbohydrates as the energy source of excellence for athletes
In long-duration efforts (both sports and work), anaerobic metabolism is practically absent, so energy is derived from the aerobic metabolism of sugars and fats. These substrates cannot be used indiscriminately, because glucose is necessary for fat consumption. The ability to use lipids, in fact, lasts as long as there are sufficient amounts of glucose available to maintain adequate activity of the Krebs cycle. Moreover, liver glycogen is not very available during physical exertion, due to hormonal factors.
The limited existing stores of carbohydrates do not exist for lipids, which are abundantly contained in adipose tissue. The muscle can use ketone bodies very well, as in fasting, but during sports competition they are scarcely available, so fats are derived from the lipolysis of adipose tissue.
Since lipids cannot support significant muscle effort without adequate carbohydrate metabolism, attention returns to glucose supply for the muscle. These sources are 3:
1. Muscle glycogen;
2. Liver glycogen;
3. Glucogenic amino acids.
Following carbohydrate-rich diets before the competition is essential for the reserves in points 1 and 2. The increase in gluconeogenesis (metabolism that produces glucose from amino acids) increases rather late. However, it can occur at sustained levels if the activity is preceded by a low-carbohydrate diet. The use of amino acids for energy purposes is not the preferable route, because their metabolism is more demanding due to the need to eliminate amino nitrogen.
It is therefore appropriate for athletes to have adequate glycogen stores to minimize protein consumption: this can be achieved with adequate carbohydrate intake the day before the competition. The presence of carbohydrates in the athlete's diet is fundamental. In their absence, ketosis and muscle protein consumption occur.
The vegan diet is particularly well suited for this purpose, due to the presence of slow-release carbohydrates (low glycemic index) and the abundance of vitamins, minerals, and antioxidant substances that act as metabolic cofactors and as inhibitors of free radicals, which damage athletes' cellular structures more because they are produced more massively by the cellular energy apparatus.
