Reserves of Carbohydrates in the Human Body
Carbohydrates, as well as simple and complex, are classified according to their availability. All those nutrients that can be used by the body are defined as available; on the contrary, the use of those not available is prevented by difficulties during digestion, absorption or metabolization.
On the other hand, the body's lipid deposits are much more abundant. An individual in good physical shape has in fact about 12 kg of fat mass, which when needed can release up to about 100,000 Kcal.
The "organism" prefers to "accumulate energy reserves in the form of lipids rather than carbohydrates for two reasons: first of all because lipids are more energetic (9 Kcal / g against 4 Kcal / g of carbohydrates); moreover, very little water is present in the adipose deposits .
Functions of carbohydrates
The primary role of carbohydrates, also called carbohydrates or carbon hydrates, is to provide energy to the body. These nutrients represent an ideal energy substrate for several reasons.
- First of all, because their metabolism does not form intermediate products or potentially harmful by-products, contrary to what happens during the catabolism of other nutrients. In fact, ketone bodies are formed from that of lipids (acidosis), from that of proteins ammonia (toxic) and from that of alcohol, acetaldehyde (also harmful for the body).
- Some tissues (primarily the nervous one) use glucose as an elective source of energy. Only in conditions of prolonged fasting does the brain use ketone bodies to meet its energy needs.
- The availability of carbohydrates as an energy substrate saves body proteins. The organism, in fact, is devoid of protein reserves to be used for energy purposes.
Despite all these valuable functions, carbohydrates are not essential nutrients, at least in the strict sense. The organism, in fact, is able to synthesize glucose from different amino acids, from lactic acid and from glycerol, according to a metabolic path called gluconeogenesis. However, a diet that is too low in carbohydrates causes excessive catabolism of fats and tissue proteins.
The consequence of excessive lipid oxidation is the accumulation of ketone bodies in the circulation. These substances are synthesized by hepatocytes starting from the acetyl-CoA produced by the oxidation of fatty acids. Under normal conditions the synthesis of ketone bodies is minimal and the small quantities produced are used for energy purposes by various tissues, such as muscles and the heart. When, on the other hand, there is a strong catabolism of fats, for example in the case of a hypoglucidic diet or prolonged fasting, the ketone bodies, produced in excess, they accumulate in the blood (ketonemia) causing acidosis. This excess is eliminated in the urine (ketonuria), however, passing in the urine, the ketone bodies attract a lot of water by osmosis, resulting in dehydration of the body.
Excessive protein catabolism leads to different but equally serious consequences:
- structural and functional deficit;
- formation of ammonia (which must be converted into urea by the liver and eliminated in the urine, resulting in hepatic and renal overwork);
- dehydration of the body.
Carbohydrates should provide 55-60% of the total daily energy intake. However, the quantity is not the only important parameter. of 10% of the total caloric intake).
The negative consequences of excessive carbohydrate consumption are manifold. First of all, when we introduce too many carbohydrates, our body increases the ability to oxidize them. Therefore, an excessive carbohydrate intake promotes an increase in energy expenditure, because the body catabolizes carbohydrates with greater speed. This argument, however, is valid only if the intake of lipids is at the same time very low.
When excessive amounts of carbohydrates are consumed, especially simple ones (sugars), the level of glucose in the blood increases (hyperglycemia). This condition rapidly promotes insulin secretion by the pancreas. This hormone acts just as quickly, causing a rapid accumulation of the lipids of the meal in the deposits. This explains why the simultaneous intake of carbohydrates and excess lipids, promotes the deposit of the latter in the fat reserves.
Furthermore, insulin inhibits the mobilization of lipids from adipose deposits and promotes rapid entry of blood glucose into adipocytes and muscle fibers.
Hypoglycemia, which follows the entry of glucose into fat and muscle cells, triggers hunger and leads to the consumption of other food. This is the reason why it is good to favor foods with a low glycemic index.
CONTINUE: the "glycemic index"
