The role of fat in overweight accumulation
Overweight can reach significant sizes – up to several tens of kilograms. Overweight and obesity is a problem that every third inhabitant of the planet faces today. In all mammals, including humans, the metabolism is adapted to the accumulation of fat as a reserve energy material. This allows you to smooth out the unevenness of the supply and consumption of energy on different days.
Excess weight and fat
Lipids can make up to 90% of the mass of human adipose tissue. Among them, 99% are triglycerides, that is, actually fats. They contain the most saturated palmitic acid. In second place are monounsaturated oleic and polyunsaturated linoleic acids: they account for more than half of the fatty acids in adipose tissue. The synthesis of fat in adipose tissue depends on the availability of intermediate metabolic products from which fat molecules are synthesized. In particular, the rate of fat formation is limited by the metabolic reactions of carbohydrates, as a result of which the constituent parts of fat molecules are formed. In addition to the synthesis of fats from blood glucose, adipose tissue can use circulating fatty acids, triglycerides and protein-fat complexes synthesized in the liver.
What dictates the need for fat? What is its role in the energy supply of the body? How do the mechanisms of fat formation and breakdown work? The answers to these questions will help to find out what role fats play in deviating from ideal body weight.
Adipose tissue is often presented as an inert mass. In fact, a fairly active metabolism takes place in it. Adipose tissue cells, like liver cells, are able to synthesize fats during periods of abundant food intake. With insufficient caloric content of food, they turn on the active mechanism of fat breakdown, freeing fatty acids for oxidation and ensuring the energy needs of the body.
Excessive consumption of carbohydrates from food has a significant effect on the synthesis of fats in adipose tissue. This is in part because an increase in blood glucose concentration causes an increase in the synthesis of insulin in the pancreas, which allows the movement of glucose molecules through the cell walls. In addition, insulin promotes increased use of glucose for glycogen synthesis. At the same time, insulin stimulates the uptake and use of glucose by fat cells and stops the breakdown of fat in the fat depot. This contributes to a sharp acceleration in the growth of adipose tissue.
However, recent studies have shown that an increase in fat in food has a much stronger effect on the growth of adipose tissue mass than excessive consumption of carbohydrates. Utilization of carbohydrates and fats varies significantly. The supply of carbohydrates in the body is small and depleted rather quickly. Carbohydrate intake regulates blood glucose and the amount of glycogen (a starch-like substance that stores carbohydrates) in the liver and muscles. Carbohydrates also have an effect on the formation of appetite. With the depletion of glycogen stores in the liver and muscles and a decrease in blood sugar levels, appetite increases.
For all the necessary energy expenditures – basic metabolism, physical work, etc. – the body “prefers” to first use up the reserves of glucose in the blood. When glucose levels decrease, glycogen stores are converted into it, first from the muscles, then from the liver. At the same time, excess proteins, if any, are consumed for oxidation and energy production. Only if all these primary reserves are used up, and new nutrients are not supplied, is the turn of the “emergency reserve” of fats.
Fats in nutrition and other processes
Only after the body has spent the necessary part of the carbohydrates and proteins absorbed from food for plastic metabolism (the construction of new cellular structures and molecules) and for energy needs, the mechanisms for the synthesis of fats from excess non-fat nutrients are turned on. And each drop of fat in excess of the amount that is necessary for the immediate needs of the body easily enters the adipose tissue. This is why healthy eating and fats are so closely related.
Fat synthesis requires less energy than glycogen synthesis. And vice versa, almost a quarter of the energy stored in it is spent on the oxidation of fat, and a little more than one tenth on the oxidation of carbohydrates. Fats are “cheaper” to store and “more expensive” to spend. This, to some extent, explains why the human body is more prone to accumulate fat. When you overeat carbohydrates, the rate of their oxidation increases, and fat oxidation slows down. An excess of carbohydrates in food is accompanied by an increase in total energy expenditure. With an excess of fat in the diet, their oxidation hardly increases. An excess of fat in food practically does not affect the oxidation of carbohydrates and does not lead to increased energy expenditure. Removing a significant portion of the fat from the diet does not significantly increase the intake of protein or carbohydrates. The body simply stops replenishing the reserves of adipose tissue.
Body weight remains stable if the proportion of energy consumed from food in the form of fat is equal to the energy obtained during its oxidation. If the amount of fat in food exceeds the possibility of its oxidation, then the excess fat will be stored in adipose tissue.
Carbohydrates can lead to the accumulation of excess weight only when they are ingested in an excessive amount, especially if they are represented by simple carbohydrates – mono- and disaccharides, which are absorbed very quickly and cause an increase in the production of insulin, which is responsible for the synthesis of fat in the body.
However, it should be borne in mind that a decrease in body weight is also accompanied by a decrease in the body’s ability to oxidize fat – the body prefers to slow down metabolism, slightly lowers body temperature, lowers physical activity and in other ways reduces energy consumption in order to preserve and even increase reserves for an “even blacker day” … Thus, in order to combat excess weight, the fat content in food should be reduced simultaneously with the reduction of the total calorie content in order to avoid the effect of the reverse accumulation of fat. After all, overweight creates a load on the body, especially on the liver.
A diet low in fat and including foods rich in complex carbohydrates and plant fiber should be part of the overweight lifestyle.