Talk about fat
Unlike carbohydrates, fats make up the body's energy reserve. Carbohydrates, which are stored in the human body in the form of glycogen, perform a more rapid function of energy supply for a short time.
The average person has a fat reserve of about 13 kg, this could be enough for 40 days of fasting in conditions of moderate physical activity. And the total reserves of glycogen in the body of a non-athlete are about 400-500 grams, which is not enough even for one day of fasting. In addition, fat is not associated with water. This, along with large reserves, determines its advantage as an energy reserve over carbohydrates. The lack of connection with water ensures the compactness of fat reserves: they are stored in anhydrous form, taking up a small volume. And for each stored gram of glycogen, you need 3-4 grams of water.
Sources of fat in the body
The sources of fat in the body are the fat that comes with food, and the synthesis of fat from carbohydrates that occurs in the liver and in the fat cells themselves. Thus, even if we completely exclude fats from the diet, our body will be able to synthesize them from other sources – carbohydrates. However, not all the fatty acids that make up fat can be synthesized by us. By analogy with essential amino acids, which we can only get from outside, the situation is also with fatty acids, some of them are also considered essential, and their source can only be food. The lack of such acids leads to a number of diseases and metabolic disorders. Whenever we limit our diet to fat, the risk of a deficiency of essential fatty acids (EFAS) increases. The reduction in the amount of fat should be compensated for by their quality, additionally introducing sources of LFA into the diet. Strictly speaking, only two essential fatty acids are linoleic and a – linolenic, and they are found in large quantities in all vegetable oils obtained from seeds, nuts, seeds, etc. Amino acids can also be converted to fat, but only indirectly, through conversion to carbohydrates, and then to fat.
What is the catabolism of fat
Fat catabolism takes place in three stages.
1. Lipolysis-hydrolysis (breakdown) of fat to glycerol and fatty acids in adipocyte fat cells, after which both glycerol and fatty acids enter the bloodstream. Lipolysis occurs during muscle work and during fasting.
2. Conversion of glycerol and fatty acids to acetyl-COA (coenzyme A). Its main function is to deliver carbon atoms with an acetyl group to the tricarboxylic acid cycle so that they are oxidized to release energy. If we draw a parallel, then fats are crude oil, and acetyl-COA is gasoline, that is, a finished product that can be used as fuel. The fastest conversion of glycerol and fatty acids to acetyl-COA occurs in the liver.
3. Acetyl-COA is converted into ketone bodies, which act as the best transporters of Acetyl-COA, and then in this form gets into various tissues, where it participates in the cycle of tricarboxylic acids for energy.
"Fat burns in the flame of carbohydrates»
Many people have heard this expression, but they don't know exactly what it means. When lipolysis increases, the rate of utilization (expenditure) of ketone bodies, which are important sources of energy for low-intensity muscle work, a carb-free diet or fasting, increases. However, the depletion of carbohydrate reserves leads to the fact that more ketone bodies are produced than disposed of. The reason lies in the fact that for the effective use of fat breakdown products, carbohydrate metabolism products are necessary: succinyl-COA and oxalic-acetic acid. In the absence of carbohydrates, there is a lack of these substances, which reduces the body's ability to use fat as an energy source. Due to the fact that our body can get glucose from amino acids, this process does not stop completely even when fasting.
Lipolysis and hormones
The fat cell, like other cells in the body, has receptors for various hormones. The interaction of certain hormones with the corresponding receptors stimulates or, conversely, inhibits lipolysis. According to their effect on fat lipolysis hormones can be divided into two groups:
1. Hormones direct the actions of adrenaline, growth hormone, insulin.
2. The indirect actions of hormones: corticosteroids, sex hormones, leptin.
Adrenaline. Adipocyte membranes contain two types of adrenoreceptors: alpha and beta. The interaction of epinephrine with both types of receptors causes a multidirectional effect on lipolysis.
- alpha-adrenoreceptor is associated with an inhibiting G-protein, which leads to inhibition of lipolysis.
- beta-adrenoreceptor is associated with a stimulating G-protein-the effect will be to stimulate lipolysis.
The ratio of alpha-and beta-adrenergic receptors depends on the individual characteristics of the body. This applies to both the body as a whole and the distribution of these receptors in different parts of the body, because of this, during the process of lipolysis, different parts of the body in different people lose weight differently. However, in General, beta-adrenoreceptors predominate in humans, so the total effect of epinephrine still leads to the activation of lipolysis. Epinephrine is produced in response to exercise and a decrease in blood sugar. That is, training and diet are a good way to manage the secretion of adrenaline to achieve the breakdown of subcutaneous fat. The action of most fat-burning supplements is based on stimulating the secretion of epinephrine or simulating its action by agonist substances, as well as on inhibiting alpha-adrenoreceptors.
Somatotropin stimulates lipolysis by acting through the adenylate cyclase system. The secretion of somatotropin increases with a decrease in blood sugar.
Insulin inhibits lipolysis, increases fat synthesis and reduces the rate of its mobilization. It is the main hormone that regulates lipogenesis, that is, the process of synthesis of fatty acids, the main source of which is carbohydrates. Low-carb and low-carb diets are effective for the simple reason that insulin secretion is minimal for most of the day.
Glucocorticosteroids have a dual effect: against the background of muscle work, they stimulate lipolysis, and at rest they inhibit it. Prolonged and prolonged stress significantly increases cortisol secretion, which remains high and at rest. Therefore, stress is one of the reasons for excessive fat accumulation.
Sex hormones. The exact mechanism of their effect on fat metabolism is not yet clear, but it is known that the action of these hormones is associated with the stimulation of the synthesis of certain proteins.
The effect of sex hormones is unidirectional-stimulating the breakdown of fat.
Hormone replacement therapy with testosterone always causes a decrease in the amount of stored fat. Castration, on the contrary, leads to an increase in its reserves. By the way, testosterone, as well as fat, belongs to the same class – lipids, because it has similar properties: for example, insolubility in water (hydrophobicity).
Leptin. By its chemical nature, it is a polypeptide hormone synthesized in adipocytes, so adipose tissue can be classified as endocrine. Leptin receptors are located in the hypothalamus and in the tissues of the reproductive system, it transmits information to the brain about the amount of fat in the body. The total effect of leptin is a decrease in appetite and increased lipolysis.
