Carbohydrates are an energy substrate NECESSARY for the survival of human beings; their quantity / percentage in the diet (whether weighted, in excess or in defect) greatly affects the general health status of the individual; furthermore, there are conditions / situations in which carbohydrates play an even more important role: one of these is aerobic physical activity.
Carbohydrates: functions and dietary role in aerobic physical activity
Animals and humans, unable to COMPLETELY comply with their glucose needs through neoglucogenesis (production of glucose from amino acids, lactic acid and glycerol), must obtain it by eating foods that contain sufficient amounts of carbohydrates, therefore: cereals ( cooked), legumes (cooked), tubers (cooked), fruits, leaves and roots.
Glucose, derived from food carbohydrates and from neoglucogenesis, is essential for tissue cellular respiration, let's see why. In the production of energy with the use of oxygen (aerobic metabolism), carbohydrates (glucose), such as fatty acids and some amino acids, are processed in Acetyl-Coenzyme A and introduced into the Krebs cycle with the aim of recharging the transporters NAD and FAD, then engaged in the oxidative phosphorylation necessary for the activation of the ATP-synthase pump. On the other hand, the Krebs cycle constitutes a real "perpetual ring", whose molecule of beginning and conclusion is represented by the OSSALACETATE; this, by binding the Acetyl-Coenzyme A, determines the start-up of the cycle itself and becomes ESSENTIAL for the correct functioning of the entire system. However (logically) the Krebs cycle must be concluded with an oxalacetate unit, these molecules often undergo deterioration; it is therefore obvious that, inactivating itself, the oxalacetate needs to be replaced. But how?
The precursors from which it is possible to obtain the oxalacetate are:
- Pyruvate - derived from glucose
- Asparagine or aspartic acid - non-essential amino acids
In basal conditions, the cycle can be perpetuated calmly drawing indiscriminately from one or the other precursor; on the other hand, the same does not happen during prolonged aerobic physical-motor activity. In this situation, given the rapidity with which cellular respiration takes place, the presence or absence of oxalacetate can become a LIMITING FACTOR; to ensure that the mechanism "DOES NOT jam" it is essential to guarantee the presence of its precursor MORE EASY and FASTER to use, or the pyruvate obtained from glucose (carbohydrates). It is undeniable that also asparagine or aspartic acid can contribute to the purpose, but considering the slowness with which they are used and their scarce presence in the diet (therefore in the organism), it can be defined with certainty that glucose ( obtained by means of dietary carbohydrates and / or by neoglucogenesis) it is a NECESSARY energy molecule for physical and physical activity and prolonged aerobic activity.
Carbohydrates for aerobic activity: how many, which and from what food sources
Once clarified WHY carbohydrates are necessary for sustaining prolonged aerobic-physical activity, it is necessary to UNDERSTAND better: how many to eat, what type and in what foods to find them.
HOW MANY CARBOHYDRATES FOR aerobic activity? We say that the quantitative estimation of carbohydrates in the diet is always empirical, therefore the relative nutritional application can prove to be even more difficult than expected. Leaving aside the overall macro-nutritional distribution of the day, in this article I think it is more appropriate to dwell on the real need to introduce carbohydrates for the purposes of performance, even if one's estimate cannot totally ignore that of the other; in fact, the availability of glucose during the performance depends above all on:
- Intrinsic stocks of muscle (fullness of muscle glycogen stocks)
- Glycemic homeostasis (fullness of liver glycogen stores)
Both of these factors are influenced by nutrition and post-prandial insulin flows in the different days before: therefore, the meal that precedes the training or the long-term endurance race (however abundant) is never enough to completely guarantee the carbohydrate request for prolonged aerobic muscle contraction. On the other hand, even assuming that the athlete's / athlete's nutrition is sufficiently distributed and balanced, it is possible to state that carbohydrates useful for the practice of prolonged aerobic activity must be introduced, however, before, during (in particular if it is a question of efforts that far exceed 60 ') and after the performance. Obviously, in order to avoid an overabundance of energy with consequent fat deposits, it is ALWAYS necessary to estimate the caloric consumption and differentiate the energy supply in the 3 moments described above. Recall that, during exertion, based on the intensity and level of training, the mixture of various energy substrates (glucose, fatty acids, amino acids) changes considerably and approximately follows these two equations:
- PERCENTAGE consumption of fatty acids and <PERCENTAGE consumption of glucose and amino acids (branched and not)
- > intensity => PERCENTAGE consumption of glucose and amino acids (branched and not) and <PERCENTAGE consumption of fatty acids.
As for the intake of carbohydrates before physical activity, I strongly suggest avoiding large portions and respecting digestion-absorption times; the sooner the meal is consumed, the greater the relative caloric importance may be; on the other hand, close to training / competition, it would be appropriate NOT to exceed 150kcal (spannometric assessment of the potential for collective digestion). During the activity, on the other hand, the intake of carbohydrates is mainly constrained by the osmotic potential of the rehydrating drink, as a source of sugars, water and mineral salts (sometimes also branched amino acids); personally, I do not recommend using solid foods during exercise (unless real and concrete needs arise), therefore, the amount of carbohydrates to be taken during training / competition corresponds to that which can be mixed in a slightly hypotonic drink of the volume of about 1.5 liters. In the meal after the effort it would be a good idea to introduce carbohydrates as soon as possible and, in any case, I suggest that you keep in mind that, often, a meal could soon arrive; in this situation the partial DISSOCUTION of nutrients with glucose prevalence in the immediate post-workout and protein-lipid prevalence in the ordinary meal is extremely convenient. Taking a brief example, assuming a consumption of about 600kcal with medium-high intensity, 60-80% of the total MUST be complied with by the supply; in practice, about 400kcal will be divided into 150-170kcal before, 60-100kcal during and 150-170kcal after.
WHAT carbohydrates for aerobic activity? In order to establish which carbohydrates are necessary for the activity, it is necessary to think about both the function they cover and the context in which they are inserted. Assuming an OPTIMAL condition, it is possible to state that:
- The carbohydrates to be taken before the aerobic activity should be of a medium-low glycemic index, in order to distribute their perfusion in the body throughout the period preceding the performance, thus avoiding the occurrence of the glycemic-insulin peak; moreover, it is better to prefer complex molecules avoiding to exceed with fructose (contained above all in the fruits and whose contribution is to correlate with that of alimentary fiber)
- Carbohydrates to be taken during aerobic activity should be of medium to high glycemic index, to allow rapid absorption and an equally fast use
- Carbohydrates to be taken after aerobic activity should be:
- High glycemic index if introduced in the immediate post-workout (first 15 minutes or at most within the first hour)
- Medium-low glycemic index if introduced after more than 60 'from the end of the session.
WHAT FOOD SOURCES would I take carbohydrates for aerobic activity? In compliance with the above, it is possible to state that the most suitable carbohydrate sources at various times are respectively:
- Much earlier (around 2h) of aerobic physical activity: foods and foods that are not very refined or contain less refined carbohydrates or composed of ingredients with moderate amounts of dietary fiber; mainly fruit (not more than 300g at a time and possibly in combination with other foods), vegetables, rye bread, whole wheat bread, basmati rice with oil, pasta with vegetables, rice with vegetables, etc.
- During aerobic physical activity: MIXTURES of maltodextrin, vitargo, saccharose, glucose and fructose
- After aerobic physical activity: foods and foods MORE refined or containing refined carbohydrates and FREE of ingredients with moderate amounts of dietary fiber; mostly plain white pasta, plain white rice, white bread, plain polenta, biscuits, bananas, plain boiled potatoes, etc.
By following all these indications it is possible not only to improve recovery, and therefore performance, but also to compose a mildly hypocaloric diet aimed at weight loss, in conjunction with aerobic-physical activity, WITHOUT the risk of running into muscle catabolism induced by carbohydrate deficiency in the diet.
