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Several researches have proposed that a prolonged period of caloric restriction (CR) may have a permanent, adverse effect on basal metabolism, fostering the development of obesity. This reported metabolic slowing has been associated with a reduction in resting metabolic rate (RMR) beyond what is predicted by the change in body composition, promoting the idea that metabolism can be permanently damaged. This systematic review investigates if prolonged CR exhibits a permanent, negative effect on basal metabolism.

Here we review the literature reporting weight loss and weight regain of individuals who were initially within a healthy weight range, such as the long-term Minnesota starvation experiment, in addition to research on chronically undernourished individuals, such as patients with anorexia nervosa, before and after recovery. Quantification of basal metabolism before and after prolonged CR revealed that body composition is the most critical factor in determining absolute RMR in neutral energy balance. Changes in energy balance induce a rapid yet reversible increase or decrease in RMR. Previous reports may have come to erroneous conclusions in favor of the metabolic damage hypothesis because they did not examine the full recovery period in the Minnesota experiment or neglected the influence of energy balance on RMR. Our findings indicate that the theory of permanent, diet-induced metabolic slowing in non-obese individuals is not supported by the current literature.