This article aims to remind readers (professionals and the uninitiated) that, despite the current tendency to favor the increase of the protein percentage in the diet to the detriment of the carbohydrate, the latter (represented by the sum of simple carbohydrates and complex) plays a FUNDAMENTAL importance in human nutrition and especially in the sustenance of sporting performance.
Carbohydrates or carbohydrates are caloric nutrients made up of carbon, hydrogen and oxygen;
IN A BALANCED REGIME THE CARBOHYDRATES COVER 55-60% OF THE FOOD RATION, they have the function of MAINTAINING THE GLYCEMIC HOMEOSTASIS (concentration of GLUCOSE in the blood) and are used above all during intense work, especially in physical exercise.
Oxidized, carbohydrates provide an average of 4.1 kcal / g REPRESENT THE MAIN ENERGETIC SUBSTRATE OF THE CENTRAL NERVOUS SYSTEM; in addition, glucides are part of the nucleic acids (ribose and deoxyribose) and some enzymes and vitamins.
Due to its importance in maintaining blood sugar, glucose (simple carbohydrate) is stored in the form of glycogen (complex carbohydrate); the latter is present in the muscles (about 70%), in the liver (about 30%) and in the kidneys (about 2%). Once the glycogen stocks have been depleted, the rate of re-synthesis of the reserves is estimated from 5% to 7% per hour; moreover, USING A BALANCED CALORIC REGIME, ASSOCIATED TO COMPLETE MUSCLE REST, at least 20 hours are necessary for a total reconstitution.
Blood glucose, whose value fluctuates under physiological conditions between 3.3 and 7.8 mmol / l (60-140 mg / 100 ml), can be defined as "the reflection of the balance between production and use". In fasting conditions, the liver and kidney continually inject glucose into the circulatory stream to prevent the blood sugar from falling below 3.3-5 mmol / l.
After taking the meal, the glucose absorbed in the intestine is poured into the blood, increasing the blood sugar up to 130/140 mg / dl; consequently, the secretion of INSULIN (FUNDAMENTAL hormone FOR GLUCOSE ENTRY IN ALL FABRICS WITH THE EXCEPT OF THE NERVOUS one) increases and promotes GLYCOGENOUS RESIN. On the contrary, when in conditions of prolonged fasting the glycaemia falls below the normal values, the body responds by lowering the production of insulin in order to preserve blood glucose and ensure the proper functioning of the central nervous system. In a similar situation, the cells that need energy production can use the lipid substrate through the B-oxidation of fatty acids, but to do this optimally, a small amount of carbohydrates is always necessary; if after a few days of fasting, blood sugar is insufficient to sustain the central nervous system, the risk of NEUROGLICOPENIA (a condition that determines CONVULSIONS, COMA AND DEATH) would increase.
In addition to favoring glycogen synthesis, insulin tends to extinguish glycogenolysis, favoring the lowering of blood glucose levels. It is of vital importance for the regulation of energy metabolism as it REPRESENTS THE ONLY HORMONE WITH A HYPOGLYCEMISTIC EFFECT, while glucagon, adrenaline, cortisol and somatotrope (hormones against regulatory or counterinsular) stimulate the degradation of reserves with a hyperglycaemic effect.
- HYPERglycaemia = stimulation of insulin secretion and inhibition of hormone release against regulators
- IPOglycemia = inhibition of insulin secretion and stimulation of hormone release against regulators
It is however wrong to consider the blood regulation of glucose as an isolated process, as it IS INTIMELY RELATED TO THE METABOLISM OF FATS AND PROTEINS; the whole is mediated by extremely sophisticated hormonal mechanisms capable of ensuring an optimal amount of metabolic energy to the body's cells.
In prolonged fasting, or following BIG PHYSICAL EXERCISE VOLUMES, glycogen stores are depleted and energy can only be provided by the oxidation of fatty acids and the ALOGINE NEOGLUCOGENESIS (transformed into pyruvate and inserted into the Krebs cycle ) resulting from the catabolism of muscle proteins. In addition to the latter, albeit to a lesser extent, glycerol, lactate and OTHER AMINO ACIDS contribute to the production of glucose (such as aspartate, valine and isoleucine which can be converted into intermediates in the Krebs cycle). A too active neoglucogenesis favors the hyperproduction of ketone bodies by the liver; in hypoglycemic conditions, the latter represent AN IMPORTANT ENRGETIC SOURCE for extrahepatic tissues, but because of their acidity, THEY CAN ALTER THE HEMATIC PH AND ENCOURAGE THE APPEARANCE OF SIDE EFFECTS INDUCED BY KETO-ACIDEMIA.
Curiosity
Many physical culture professionals and some nutrition experts evaluate the Glucids as NON-essential elements, as their physiological homeostasis is partly guaranteed by the process of neoglucogenesis. However, observing the energy production cycle and evaluating the intensity of metabolic activation in endurance athletes, it is appropriate to specify that:
"in the Krebs cycle, a fundamental step in cellular respiration capable of producing NADH and FADH2 (which will subsequently enter the respiratory chain), the starting substrate Acetyl-Coenzyme A (deriving from glucose glycolysis and from the B-oxidation of fatty acids) NEEDED of an immediate CONDENSATION with the OXALACETATE by the citrate synthase Oxalacetate is the starting and arrival molecule of the Krebs cycle, and can be obtained by demolishing the asparagine and the aspartic acid (non essential amino acid), MA in a much faster and more effective way from the conversion of the PIRUVATO by the pyruvate carboxylase.
Considering that pyruvate is a molecule derived from the glycolysis of carbohydrates (macronutrients introduced with food in a rapid and selective manner), while asparagine is an amino acid present in limited quantities in foods (and its synthesis is not new anyway). a process of rapid use), in my opinion it is possible to state that in cellular respiration and especially in the energy metabolism of endurance athletes carbohydrates perform a function which is nothing short of fundamental ".
Glycemic index
The carbohydrate metabolism can be expressed in terms of the glycemic index (IG); this index highlights the different impact of carbohydrates on blood glucose and insulin levels. In particular, the IG is equal to the ratio between the glycemic response of a given food and the reference value, multiplied by 100. The reference food can be white bread or glucose and the carbohydrate dose considered is equal to 50 grams.
The IG is useful to define the food quality of the pre-race meal (which must have a low metabolic speed), and of the IMMEDIATE one (within an hour) post-race (which, on the contrary, will be characterized by the speed of digestion, of absorption and metabolisation EVEN INDEPENDENT very high insulin). Studies carried out on athletes who practice moderate and prolonged activities have shown that the intake of carbohydrates during sports activity does NOT positively influence physical activity in terms of metabolism and performance (even if the potential for saving and restoring the body is not mentioned). muscle glycogen); it therefore seems more logical to choose to eat meals with high amounts of low GI carbohydrates before serving.
Bibliography:
- Human physiology - edi ermes - chapter 15
- Nutrition physiology - pages 401-403
