Pathogenesis of ObesityObesity Energetics: Body Weight Regulation and the Effects of Diet Composition
Section snippets
Components of Daily Energy Expenditure
There are 3 components of daily energy expenditure: the thermic effect of food, physical activity expenditure, and resting energy expenditure (REE) (Figure 1A).
Influence of Exercise on Energy Expenditure and Body Weight
While often considered a first-line treatment option for obesity, large amounts of exercise are required to result in a modest degree of average weight loss.15 However, exercise results in preferential loss of body fat and maintenance of fat-free mass compared with diet-induced weight loss,16, 17 but exercise does not appear to prevent the slowing of metabolic rate during weight loss.18 Exercise interventions typically result in an average weight loss that is less than expected based on the
Influence of Energy Intake on Energy Expenditure
Reductions in energy intake lead to decreased energy expenditure to a degree that is often greater than expected based on changes in body composition or the thermic effect of food.25, 26 This phenomenon has been called adaptive thermogenesis or metabolic adaptation and it may continue for years after energy balance is reestablished at a lower weight,27, 28, 29 although controversy remains regarding its persistence.30, 31 The mechanistic basis of metabolic adaptation is unclear, but it may be
Influence of Dietary Macronutrients on Energy Balance and Body Composition
The energy released during carbohydrate, fat, and protein oxidation within the body can be equated to the energy derived from their combustion in a bomb calorimeter, with suitable corrections for the differing thermodynamic constraints and the end products of the reactions. In other words, “a calorie is a calorie” when macronutrients are oxidized either in the bomb calorimeter through combustion or via the intricate biochemical pathways of oxidative phosphorylation inside cells.
However,
Feedback Control of Energy Intake
While there is a growing consensus that human energy expenditure is actively controlled to resist weight loss,26 the evidence for active control of energy intake is less clear. Observations regarding long-term precision of calorie balance and relative weight stability have been offered in support of energy intake feedback control, but these observations also have alternative explanations69, 70, 71 relying solely on energy expenditure adaptations and correspond to a “settling point” model of
Static, Settling Point, and Set-Point Models of Human Body Weight Regulation
Long-term feedback control of energy intake and expenditure has profound implications for body weight regulation and our understanding of obesity treatment. Without such feedback control mechanisms, body weight dynamics correspond to the static “calories in, calories out” model, where energy intake and expenditure are independent variables and weight changes, or related homeostatic signals like leptin, are assumed to have negligible effects on energy intake or expenditure.
Figure 3A illustrates
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Conflicts of interest K.D.H. has received funding from the Nutrition Science Initiative to investigate the effects of ketogenic diets on human energy expenditure. K.D.H. also has a patent on a method of personalized dynamic feedback control of body weight (US Patent No. 9,569,483; assigned to the National Institutes of Health). J.G. has no conflicts of interest to disclose.
Funding This research was supported by the Intramural Research Program of the National Institutes of Health, National Institute of Diabetes & Digestive & Kidney Diseases.