Abstract
Metabolic adaptations occur with weight loss that result in increased hunger with discordant simultaneous reductions in energy requirements—producing the so-called energy gap in which more energy is desired than is required. The increased hunger is associated with elevation of the orexigenic hormone ghrelin and decrements in anorexigenic hormones. The lower total daily energy expenditure with diet-induced weight loss results from (1) a disproportionately greater decrease in circulating leptin and resting metabolic rate (RMR) than would be predicted based on the decline in body mass, (2) decreased thermic effect of food (TEF), and (3) increased energy efficiency at work intensities characteristic of activities of daily living. These metabolic adaptations can readily promote weight regain. While more experimental research is needed to identify effective strategies to narrow the energy gap and attenuate weight regain, some factors contributing to long-term weight loss maintenance have been identified. Less hunger and greater satiation have been associated with higher intakes of protein and dietary fiber, and lower glycemic load diets. High levels of physical activity are characteristic of most successful weight maintainers. A high energy flux state characterized by high daily energy expenditure and matching energy intake may attenuate the declines in RMR and TEF, and may also result in more accurate regulation of energy intake to match daily energy expenditure.
Highlights
Obesity, classified as a disease [1], has become a global health problem with attendant increased risk of other chronic diseases
Total daily energy expenditure (TDEE) is a function of four components: resting metabolic rate (RMR: the energy expenditure required for cellular processes necessary for life as measured when an individual is lying quietly and awake in a post-absorptive state), the thermic effect of food (TEF: the increase in energy expenditure above RMR in response to food ingestion), non-exercise activity thermogenesis (NEAT: energy expenditure above RMR required to support the activities of daily living as well as fidgeting), and exercise energy expenditure (ExEE: energy expended above RMR necessary for performing exercise)
We have shown that RMR decreases significantly when energy balance is maintained with cessation of exercise and simultaneous reduction in energy intake [118]
Summary
Classified as a disease [1], has become a global health problem with attendant increased risk of other chronic diseases. The etiology of obesity is complex, but fundamentally results from excess energy availability relative to energy expenditure, subsequently leading to energy storage, largely in the form of triacylglycerol molecules in adipocytes. Successful treatment must fundamentally involve a shift in energy balance such that total cellular energy expenditure exceeds availability. While this concept of energy balance may appear relatively simple, it has many layers of complexity that should be understood by scientists and practitioners in their attempts to provide the best available approaches to treating obesity. (2) What lifestyle interventions can be used to counter these metabolic adaptations that promote weight regain, affording overweight and obese individuals greater opportunity to achieve relatively “permanent” (rather than transitory) improvements in body composition and health status? The current review will focus on two important questions: (1) What metabolic adaptations make long-term maintenance of weight loss so difficult? and (2) What lifestyle interventions can be used to counter these metabolic adaptations that promote weight regain, affording overweight and obese individuals greater opportunity to achieve relatively “permanent” (rather than transitory) improvements in body composition and health status?
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