Dynamic changes in energy expenditure in response to underfeeding: A review

Abstract

The observation that 64% of English adults are overweight or obese despite a rising prevalence in weight-loss attempts, suggests our understanding of energy balance is fundamentally flawed. Weight-loss is induced through a negative energy balance; however, we typically view weight change as a static function, in that energy intake and energy expenditure are independent variables, resulting in a fixed rate of weight-loss assuming a constant calorie deficit. Such static modelling provides the basis for the clinical assumption that a 3500 kcal deficit translates to a 1lb weight-loss. However, this "3500 kcal rule", is consistently shown to significantly overestimate weight-loss. Static modelling disregards obligatory changes in energy expenditure associated with the loss of metabolically active tissue i.e., skeletal muscle. Additionally, it disregards the presence of adaptive thermogenesis, the underfeeding-associated fall in resting energy expenditure beyond that caused by loss of fat-free mass. This metabolic manipulation of energy expenditure is observed from the onset of caloric restriction to maintain weight at a genetically pre-determined set point. As a result, the observed magnitude of weight-loss is disproportionally less, followed by earlier weight plateau, despite strict compliance to a dietary intervention. By simulating dynamic changes in energy expenditure associated with underfeeding, mathematical modelling may provide a more accurate method of weight-loss prediction. However, accuracy at an individual-level is limited due to difficulty estimating energy requirements, physical activity and dietary intake in free-living individuals. In this paper, we aim to outline the contribution of dynamic changes in energy expenditure to weight-loss resistance and weight plateau.