How Dieting (Energy Restriction) Affects Your Metabolic Rate
While dieting does not lead to a permanent suppression in RMR there can be a temporary, and relatively small, suppression while following reduced energy intakes. However, since this suppression disappears following cessation of negative energy balance it is not evidence for set-point, starvation-response, and metabolic adaptation theories.
Poehlman explains “the data are completely equivocal—RMR doesn’t always drop with energy restriction… the trend [however] is that the greater the [magnitude of] energy restriction the greater the potential reduction in adjusted RMR.”[i] Another review on this topic concludes that for subjects on low-calorie diets (LCDs) of >/=1,200 calories the reduction in adjusted RMR (if any) is modest at 0% to 5%. Conversely, a 5% to 15% reduction can be seen with very low calorie diets (VLCDs), which by definition are </=800 calories.[ii] The majority of dieters will see little or no suppression in RMR.
De Groot investigated whether a slimming diet that alternated low and normal energy intake (a rotation diet) would counteract a decrease in 24-hour energy expenditure (EE) compared to subjects following a low calorie diet (it did not). De Groot concluded, “Because the decrease in 24EE could be explained by changes of body weight, energy intake (thermic effect of food) and physical activity, there was no need to theorize about the influence of other adaptive mechanisms.” [iii] De Groot’s findings are not surprising since it takes 7- to 14-days on maintenance level calories (appropriate for current body weight) for a subject’s RMR to normalize following energy restriction.[iv]
In my previous post I offered three review studies on the effects of weight loss on metabolic rate, and another three studies (one a review) that looked at metabolic rate of chronically undernourished populations. These studies all debunk the notion of set-point. In my handout, Set-point, starvation response and metabolic adaptation theories are not supported by the literature, I discuss two known problems (one statistical, one methodological) with some of the research that appeared to support the notion of set-point.
Note that the paper by Leibel[vi], which may be the most quoted among advocates of the set-point idea is one of the studies criticized for statistical problems, "Leibel et al, reported that weight loss caused a reduced ratio of RMR to FFM; however, when the authors adjusted RMR for changes in FFM and FM by using a regression-based analysis [ANCOVA], the changes in RMR were not significant..."[v]. This statistical issue was well known years before Leibel’s paper was published.
[i] Poehlman ET, Melby CL, Goran MI. The Impact of Exercise and Diet Restriction on Daily Energy Expenditure. Sports Med. 1991;11:78-101.
[ii] Prentice A, Goldberg GR, Jebb SA, et al. Physiological Responses to Slimming. Proc Nutr Soc. 1991;50:441-458.
[iii] de Groot LC, et al. Adaptation of energy metabolism of overweight women to altering and continuous low-energy intake. Am J Clin Nutr 1989;50(6):1314-23.
[iv] Weinsier RL, et al. Do adaptive Changes in Metabolic Rate Favor Weight Regain in Weight Reduced Individuals? Am J Clin Nutr. 2000;72:1088-1094.
[v] Weinsier RL, et al. Energy expenditure and free-living physical activity in black and white women: comparison before and after weight loss. AJCN 2000;72:1088-94.
[vi] Leibel RL, et al. Changes in energy expenditure resulting from altered body weight. N Engl J Med 1995;332:621-8.