In humans, the daily total energy expenditure (total return = CO) can be represented as a set of three components:
1) free energy expenditure (basal metabolic rate = OO) is the energy required for the normal functioning of cells and organs after receipt of the necessary materials, including the rest (almost 70% of CO); 2) The thermic effect of food: energy expenditure associated with digestion and absorption of food, as well as increased sympathetic tone after a meal (about 10% of CO); 3) energy costs associated with physical activity: energy capacity of any mechanical work (exercises and normal daily activity), involuntary activity (eg, emotional stress), spontaneous muscle contractions, as well as maintaining body posture (about 20% of CO).
Indicators of PA vary significantly, depending on how much energy needs to tissue or organ. Thus, the bodies that reside in the active state, such as liver, intestine, brain, kidneys or heart, it takes more energy per gram of tissue. In lean adults in these organs is almost 75% of the total metabolism, although the mass they make up only 10% of the total body weight. While in skeletal muscle metabolism by 20%, despite the fact that the mass they constitute 40% of total body weight, and adipose tissue metabolism by 5% to 20% component of body weight. Factors influencing changes in energy metabolism in obesity have been carefully studied in crossover studies.
PA in obese individuals usually have higher values than lean people with the same growth. This is due to the fact that obesity increases the weight not only fat but also the tissues that do not contain fat cells. In the study of lean and obese volunteers have found that obesity is associated with a small (~ 75 kcal in a day), but perhaps a decisive reduction of the thermal effect of food, which may influence the development of insulin resistance and decreased sympathetic tone in adiposity. An obese person requires the same amount of energy that thin one for identical work, if body weight is stable. Furthermore, obese people spend even more energy than thin, due to the need to "wear" the body with greater mass. However, it is not known whether people are spending, less obese than the lean, overall energy for daily physical activity, since they are generally less active.
Two large studies conducted with children, have shown that the metabolic rate during sleep, GS, energy consumption for daily physical activity and CO are the same as in lean and obese children (adjusted for constitutional features). In general, the results of a large number of studies suggest that obese people, there is no obvious metabolic disorders. Significant changes in GS and CO were found even in patients resistant to diet, that is not able to reduce their weight, despite compliance with stringent low-calorie diet. Perhaps these patients are unknowingly not controlled food intake and could consume twice as many calories as instructed on the power circuit.
Although significant metabolic disorders in adults and children who are obese, have not been found, it is possible that still some specific changes in the utilization of energy cause the pathogenesis of obesity. However, a causal relationship between changes in energy consumption and the subsequent development of obesity is difficult, since all the work on the study of metabolism were performed in a short time, which made it impossible to fix the violations that occur in certain periods of life. In addition, the identification of even small but clinically significant metabolic disorders currently limited by the capabilities of research technologies. However, most studies do not support the view that the metabolic disorder predisposes to obesity.
In one long-term study of children found that a three-month daily with infants was 21% lower in those who subsequently had an overweight, but this finding is not confirmed by many subsequent works. Thus, the long study 126 Pima Indians showed that among those who figure was three times lower than GS-level set was a higher rate of increase in body weight of 10 kg over 1-4 years. At the same time in the Baltimore Longitudinal Study study involving 775 men have been found no correlation between the initial index level of the TOE and weight change over the next 10 years.
Although weight gain is always associated with high energy consumption compared to energy consumption, the number of pounds by which people get better with overeating, may be due to genetics, that is, some people are more likely to be overweight than others. Bouchard et al. found that prolonged use of 1000 "extra" calories per day led to a different, albeit similar, increase in body weight in monozygotic twins in the group of 12 pairs. This difference may be due to varying thermogenic response to excessive food intake in twins.
Recent studies have shown that increasing the amount of adipose tissue in response to excessive consumption of food within 8 weeks of back-energy proportional to the change in the involuntary processes in the body. That is, these costs with excessive food intake may be genetically predetermined to prevent or limit excessive weight gain in some people, and realized in the form of a large leakage energy consumption. Losing weight through diet reduces the PA, which contributes to the reverse weight gain. The existence of this phenomenon led to the development of the theory of «set-point» («set-point"), whose essence lies in the fact that a person's weight is predetermined, and therefore decrease (or increase) of weight leads to a decrease (or increase) the metabolic rate and recovery body weight to a certain level.
Low-calorie food like lean and obese people causes decrease in GS 15-30%, but this can not be explained by the decrease in body weight or amount of tissue that contains no fat, and is a normal reaction to metabolic adaptation in response to a lack of energy . However, the decrease in GS below a certain level is a transient state appears only at a negative energy balance and weight stabilization in place. Many studies have demonstrated that prolonged maintenance of a stable weight after its reduction does not lead to a substantial reduction in CO and PA at a time when there is adaptation of the organism to new conditions.
Analysis of 15 studies on this topic revealed that the rate of PA was similar in humans, long-term obesity and people who had never had. Thus, reducing the absolute numbers of CO and PA, appearing at weight reduction may contribute to the recurrence of accumulation of body weight, whereas the reduction of metabolism, most likely a manifestation of the adaptive response of the organism.