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


In February, Alexandra Martin's latest research paper, "Tissue losses and metabolic adaptations both contribute to the reduction in resting metabolic rate following weight loss," was published in the International Journal of Obesity . She investigated the contribution of changes in energy-consuming tissues and organs and metabolic adaptations to the reduction in resting metabolic rate following weight loss.

Resting metabolic rate refers to the amount of energy our body expends at rest, i.e., the energy needed to keep the organism alive. Energy-expending tissues and organs include skeletal muscle, adipose tissue, bone, brain, and internal organs.

A secondary analysis of data from the Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy study examined changes in resting metabolic rate (RMR), body composition, and metabolic hormones. The analysis focused on changes during the initial 12-month period of caloric restriction, which was accomplished by reduced intake of energy from food. By multiplying changes in the size of energy-expending tissues and organs with their tissue-specific metabolic rates, the impact of tissue losses on the decline in resting metabolic rate was determined. Additional reductions in resting metabolic rate were defined as metabolic adaptations.

While study participants lost 7.3 ± 0.2 kg over 12 months, resting metabolic rate decreased by 101 ± 12 kcal/day. On average, 60% of the reduction in resting metabolic rate was explained by the loss of energy-expending tissues, whereas 40% was due to metabolic adaptations.

Loss of skeletal muscle mass was not significantly associated with changes in resting metabolic rate. In contrast, the loss of adipose tissue was positively associated with reductions in resting metabolic rate, as were reductions in the metabolic hormones leptin, triiodothyronine, and insulin.

However, how are these results to be classified in concrete terms? During weight loss, both tissue loss and metabolic adjustments contribute to the reduction in resting metabolic rate, although to varying degrees. Contrary to popular belief, it appears to be the loss of adipose tissue, rather than skeletal muscle, that explains the reduction in resting metabolic rate following weight loss.

For more information, you will find the full-text here.