Tissue losses and metabolic adaptations both contribute to the reduction in resting metabolic rate following weight loss

Abstract

Objective To characterize the contributions of the loss of energy-expending tissues and metabolic adaptations to the reduction in resting metabolic rate (RMR) following weight loss. Methods A secondary analysis was conducted on data from the Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy study. Changes in RMR, body composition, and metabolic hormones were examined over 12 months of calorie restriction in 109 individuals. The contribution of tissue losses to the decline in RMR was determined by weighing changes in the size of energy-expending tissues and organs (skeletal muscle, adipose tissue, bone, brain, inner organs, residual mass) assessed by dual-energy X-ray absorptiometry with their tissue-specific metabolic rates. Metabolic adaptations were quantified as the remaining reduction in RMR. Results RMR was reduced by 101 ± 12 kcal/d as participants lost 7.3 ± 0.2 kg (both p < 0.001). On average, 60% of the total reduction in RMR were explained by energy-expending tissues losses, while 40% were attributed to metabolic adaptations. The loss of skeletal muscle mass (1.0 ± 0.7 kg) was not significantly related to RMR changes (r = 0.14, p = 0.16), whereas adipose tissue losses (7.2 ± 3.0 kg) were positively associated with the reduction in RMR (r = 0.42, p < 0.001) and metabolic adaptations (r = 0.31, p < 0.001). Metabolic adaptations were correlated with declines in leptin (r = 0.27, p < 0.01), triiodothyronine (r = 0.19, p < 0.05), and insulin (r = 0.25, p < 0.05). Conclusions During weight loss, tissue loss and metabolic adaptations both contribute to the reduction in RMR, albeit variably. Contrary to popularly belief, it is not skeletal muscle, but rather adipose tissue losses that seem to drive RMR reductions following weight loss. Future research should target personalized strategies addressing the predominant cause of RMR reduction for weight maintenance.

Peripheral thyroid hormone deiodination: Entry points to elucidate mechanisms of metabolic adaptation during weight regain

“…This contention is supported by findings from a revisit to the Minnesota Starvation Experiment of a positive relationship between diminished mass‐adjusted resting EE and the degree of fat depletion (but not with the degree of FFM depletion) both during weight loss and weight regain [2]. It is also supported by more recent studies indicating an association between diminished mass‐adjusted EE and the loss of fat mass during caloric restriction [5–7]. These findings are consistent with the concept of two distinct control systems underlying adaptive thermogenesis in response to energy deficit [8].…”

Effectiveness of Adherence to a Mediterranean Diet in the Management of Overweight Women: the Prospective Interventional Cohort Study

“…Contrary to popular belief, it is not skeletal muscle but rather adipose tissue losses that seem to drive RMR reduction following weight loss [18]. FFM, TBW, and BM values decreased during a three-month program in each group (Table 1.).…”

Effectiveness of Adherence to a Mediterranean Diet in the Management of Overweight Women: The Prospective Interventional Cohort Study

“…Investigations [ 36 , 37 ] have shown that a low-carb diet is more effective at reducing visceral fat than a low-fat diet. Furthermore, contrary to popular belief, it is not skeletal muscle but rather adipose tissue losses that seem to drive RMR reduction following weight loss [ 38 ]. Furthermore, Yener et al (2017) [ 39 ] assert that cortisol can increase the visceral fat the body stores so that stress reduction may influence fat loss.…”