Metabolic Adaptation - How the Body Reacts to an Energy Deficiency

According to theory, in order to lose 1 kg of fat, it is necessary to decrease the absorption of calories by about 7000 kcal per month due to metabolic adaptation. However, the negative balance of energy in a week itself, which gives 1000 calories a day. Unfortunately, this is only a simplified assumption. The caloric deficit will not only affect the burning of fat. The body also gets energy from glycogen and protein.

N. Casanova et al. in their publication discussed muscle-deficient body mass as an appetite-stimulating factor. In many studies, a correlation was observed between the amount of muscle-deficient body mass and the amount of energy consumed (the more muscle-deficient body mass, the more intake of energy). The authors suggest that this effect is directly related to PPM. In the end, the greater the amount of muscle-deficient body mass as an appetite-stimulating factor, the higher the value of PPM. This may explain why when we lose muscle-deficient body mass, the more energy we consume (the greater the muscle-deficient body mass, the higher the intake of energy) in many studies. Research by R.G. Vink and colleagues showed that 75 participants followed a reducing diet for 12 weeks (1250 kcal/day) and for 5 weeks (500 kcal/day). After this period, participants underwent a 4-week weight stabilization period. Nine months after the end of the study, body composition and weight were checked for the last time. The groups (diet 1250 kcal vs. 500 kcal) did not differ significantly in terms of the number of kilograms lost and gained after the study. However, people in the 500 kcal/day group lost more muscle-deficient body mass compared to the 1250 kcal/day group. The loss of muscle-deficient body mass in all participants was associated with weight gain after weight loss. This suggests that a significant loss of muscle tissue during the weight loss process is a negative prognosis.

A. B. Evert and M. J. Franz explain why maintaining the outcomes of a reduction diet often fails, taking into account the changes in the proportions of appetite-regulating hormones that are associated with the loss of kilograms. A negative energy balance triggers a series of adaptive mechanisms aimed at preventing hunger (as perceived by the body). Body mass is maintained by the work of appetite-regulating hormones secreted in the digestive system, pancreas, and fat tissue. After just 24 hours of beginning a reduction program, the concentration of leptin, an appetite-suppressing hormone, decreases, while the concentration of ghrelin, an appetite-stimulating hormone, increases. In a study conducted in 2011, the levels of appetite-regulating hormones were assessed in overweight individuals before starting a reduction program and 10 and 62 weeks after its completion (P. Sumithran et al. 2011). After finishing the diet, the levels of appetite-regulating hormones did not return to baseline levels, and participants reported experiencing greater hunger and appetite than before. Researchers concluded that it is important for maintaining body weight after weight loss to find a way to counteract these changes.

The effectiveness of a reduction diet is closely related to the individual characteristics and predispositions of the person. Among these characteristics is the level of intensity with which a person experiences satiety. Two groups of phenotypes, low- or high-satiety behavioral phenotypes (LSP, HSP), are distinguished. LSP is a phenotype that does not feel satiety after eating (and sometimes even senses increased hunger). People with this phenotype often declare maintaining appetites at the same level throughout the day. Compared to people with the HSP phenotype, people with the LSP phenotype tend to have a stronger preference for high-energy food, eat meals with higher calorie content, and have difficulty adhering to the diet guidelines.