Carbohydrates are an energy substrate NECESSARY for human survival ; their quantity/percentage in the diet (whether weighted, in excess or in deficiency) significantly affects the general state of health 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
Carbohydrates are energetic macronutrients produced autonomously by plant organisms (autotrophs); on the other hand, the survival of animal organisms also depends on the availability of these molecules, in particular glucose , which represents the “FUEL” of body tissues (including the nervous system -SN).
Animals and humans, not being able to COMPLETELY meet their glucose needs through neoglucogenesis (production of glucose from amino acids , lactic acid and glycerol ), must obtain it by eating foods that contain sufficient quantities of carbohydrates, therefore: cereals ( cooked), legumes (cooked), tubers (cooked), fruits , leaves and roots.
Glucose, deriving from dietary carbohydrates and neoglucogenesis, is essential for the cellular respiration of tissues, 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 into Acetyl-Coenzyme A and entered 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 synthetase pump . On the other hand, the Krebs cycle constitutes a true ” perpetual ring “, whose starting and ending molecule is represented by OXALACETATE; this, by binding Acetyl-Coenzyme A , determines the start of the cycle itself and becomes ESSENTIAL for the correct functioning of the entire system. Although (logically) the Krebs cycle must end with an oxaloacetate unit, these molecules often undergo deterioration; it is therefore obvious that, by becoming inactivated, the oxaloacetate needs to be replaced. But how?
The precursors from which oxaloacetate can be obtained are:
- Pyruvate – derived from glucose
- Asparagine or aspartic acid – non-essential amino acids
In basal conditions, the cycle can easily perpetuate itself by drawing on one precursor or the other without distinction; on the other hand, the same does not happen during prolonged aerobic physical-motor activity. In this situation, given and considered the rapidity with which cellular respiration occurs, the presence or absence of oxaloacetate can become a LIMITING FACTOR; to ensure that the mechanism “DOES NOT jam” it is essential to guarantee the presence of its EASIEST and QUICKEST precursor to use, i.e. pyruvate obtained from glucose (carbohydrates). It is undeniable that asparagine or aspartic acid can also 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 through dietary carbohydrates and/or by neoglucogenesis) constitutes an energy molecule NECESSARY for prolonged and aerobic physical-motor activity.
Carbohydrates for aerobic activity: how many, which ones and from what food sources
Once it has been clarified WHY carbohydrates are necessary to support prolonged aerobic physical-motor activity, it is necessary to better UNDERSTAND: how many to eat, what type and in what foods to find them .
How many carbohydrates for aerobic activity?
Let’s say that the quantitative estimate 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 believe it is more appropriate to focus on the real need to introduce carbohydrates for performance purposes, even if the estimate of one cannot totally ignore that of the other; in fact, the availability of glucose during performance depends above all on:
- Intrinsic muscle stores (fullness of the muscles’ glycogen stores)
- Glycemic homeostasis(fullness of liver glycogen stores )
Both of these factors are influenced by the diet and post-prandial insulin flows of the previous several days: therefore, the meal that precedes training or a prolonged endurance race (however abundant) is NEVER sufficient to completely guarantee the carbohydrate requirement for sustained aerobic muscle contraction . On the other hand, even assuming that the sportsman/athlete’s diet is sufficiently distributed and balanced , it is possible to state that the carbohydrates useful for the practice of prolonged aerobic activity must in any case be introduced before, during (in particular, if of efforts that well 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 calorie consumption and differentiate the energy intake in the 3 moments described above. Let us remember that, during effort, based on the intensity and level of training, the mixture of the various energy substrates (glucose, fatty acids, amino acids) changes considerably and approximately follows these two equations:
- < intensity = > PERCENTAGE consumption of fatty acids and < PERCENTAGE consumption of glucose and amino acids (branched and non-branched)
- > intensity = > PERCENTAGE consumption of glucose and amino acids (branched and non-branched) and < PERCENTAGE consumption of fatty acids.
As regards the intake of carbohydrates before physical activity, I strongly suggest avoiding large portions and respecting the 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 advisable NOT to exceed 150 kcal (spannometric evaluation of the collective digestion potential ).
During activity, however, carbohydrate intake is mainly limited by the osmotic potential of the rehydrating drink, as a source of sugars , water and mineral salts (sometimes also branched chain amino acids ); Personally, I advise against using solid foods during exercise (unless real and concrete needs arise), therefore, the quantity of carbohydrates to be taken during training/competition corresponds to that which can be mixed in a slightly hypotonic drink with a volume of approximately 1.5 litres.
In the meal after the effort it would be a good idea to introduce carbohydrates as quickly as possible and, in any case, I suggest keeping in mind that, often, shortly thereafter the time for a main meal could arrive; in this situation, the partial DISSOCIATION of nutrients with carbohydrate prevalence in the immediate post-workout and protein- lipid prevalence in the ordinary meal proves to be extremely convenient . Giving a brief example, assuming a consumption of around 600 kcal with medium-high intensity, 60-80% of the total MUST be met by nutrition; in practice, around 400 kcal will be divided into 150-170 kcal before, 60-100 kcal during and 150-170 kcal after.
What carbohydrates for aerobic activity?
To establish which carbohydrates are necessary for the activity it is necessary to think both about the function they have and the context in which they are inserted. Assuming an OPTIMAL condition, it is possible to state that:
- The carbohydrates to be taken before aerobic activity should have a medium-low glycemic index , in order to distribute their perfusion in the body for the entire period of time preceding the performance, thus avoiding the occurrence of the glycemic – insulin peak ; furthermore, it is better to prefer complex molecules and avoid excess fructose (contained mainly in fruits and whose intake is correlated to that of dietary fibre ).
- The carbohydrates to be consumed during aerobic activity should have a medium- high glycemic index , to allow rapid absorption and equally rapid use.
- The carbohydrates to be consumed after aerobic activity should be:
- High glycemicindex if introduced immediately post-workout (first 15′ or at most within the first hour);
- With a medium- low glycemic indexif introduced more than 60 minutes after the end of the session.
From what food sources should you take carbohydrates for aerobic activity?
In compliance with what has been stated so far, it is possible to state that the most suitable sources of carbohydrates at various times are respectively:
- Much before (about 2h) aerobic physical activity: unrefined foods and foods or foods containing unrefined carbohydrates or composed of ingredients with fair quantities of dietary fiber ; mainly fruit (no more than 300 g at a time and possibly in combination with other foods), vegetables , rye bread , wholemeal bread , basmati rice with oil, pasta with vegetables , rice with vegetables etc.
- During aerobic physical activity: MIXTURES of maltodextrin , vitargo , sucrose , glucose and fructose.
- After aerobic physical activity: foods and foods that are MORE refined or contain refined carbohydrates and WITHOUT ingredients with fair quantities of dietary fibre; mainly unseasoned white pasta, unseasoned white rice , white bread , unseasoned polenta , biscuits , bananas , unseasoned boiled potatoes etc.
By following all these indications it is possible NOT only to improve recovery, therefore performance, but also to compose a possible mildly low-calorie diet aimed at losing weight, in conjunction with aerobic physical-motor activity, WITHOUT running the risk of running into muscle catabolism induced by insufficiency of carbohydrates in the diet.
