A slow weight loss and a slight reduction in intake are not the same as a sudden loss caused by a strict diet in a few days. The latter is accompanied by a decrease in bone and muscle mass and many muscle proteins, which reduces caloric expenditure. In addition, it lowers the production of heat that is released from said thermogenic reactions. Inducing thermogenesis as a result of an adequate diet will cause essential changes at the hypothalamic level. In contrast, a caloric restriction would have opposite effects, decreasing food-induced thermogenesis.
The secretion of hormones will be crucial to modify nerve activity and, therefore also thermogenesis. Said hormonal variations are generally due to the decrease in insulin and leptin, contrary to the increase in ghrelin and the reduction in the transforming action of T4 in T3. In addition, low insulin levels inhibit hypothalamic nerve activation, optimizing the thermogenesis of brown adipose tissue and the transformation of white to beige adipocytes.
Leptin is the primary hormone in stimulating, through its actions, the hypothalamic nuclei. The decrease in this hormone will decrease the thermogenesis of brown adipose tissue and the transformation of white to beige adipocytes. On the other hand, the increase in ghrelin generated by the decrease in intake will suppress the activation of brown adipose tissue, the effect of converting white to beige adipocytes, and the muscle thermogenic action.
Hypothalamic control of adaptive thermogenesis
The hypothalamic centers during fasting and eating are decisive. Given the decrease in food intake, the body decreases the sympathetic activity of the hypothalamic nuclei. This produces a decrease in the activity of brown adipose tissue and the transformation of white adipocytes to beige adipocytes.
By reducing this activity, the basal metabolism also decreases, and therefore the loss of fat tissue is also little influenced? That is why such food deprivation or diets deficient in protein will not meet the expected objectives, alarming our nervous system, retaining white adipocytes, and worse still, losing muscle mass due to fully degradative processes, affecting or generating changes profound in our body composition.
It is also true that thermogenesis will be higher in trained people than in sedentary people. This due to its muscle tissue and the thermogenic effects that it generates; before this, taking into account, the somatotype of the subject is an important aspect.
Through exercise-induced thermogenesis increasing caloric expenditure due to physical exercise and maintaining or reducing food intake will lose excess fat. There are two mechanisms in weight loss, the increase in muscle tissue and the adaptive changes produced in adipose tissue.
The increase in muscle tissue is produced by increasing basal metabolism during exercise and once it is finished. The HIIT method, for example, is very characteristic of this with its post-exercise or EPOC effect.
The main reason would be the increase in muscle mass and consequently the increase in energy consumption of this tissue. Herein lies then the importance of strength training as a complement in the loss of fat overweight.