Adaptive reduction in thermogenesis and resistance to lose fat in obese men

Adaptive thermogenesis is defined as a greater than predicted change in energy expenditure in response to changes in energy balance. This issue is particularly relevant in the context of a weight-reducing programme in which diminished thermogenesis can be sufficient to compensate for a prescribed decrease in daily energy intake. In the present pilot study, we investigated the adaptive reduction in thermogenesis in resting state that appears to favour resistance to further weight loss. Eight obese men (mean BMI: 33.4 kg/m2, mean age: 38 years) participated in this repeated-measures, within-subject, clinical intervention. They were subjected to a weight-loss programme that consisted of a supervised diet (-2930 kJ/d) and exercise clinical intervention. The phases investigated were as follows: (i) baseline, (ii) after 5 (SE 1) kg loss of body weight (phase 1), (iii) after 10 (SE 1) kg weight loss (phase 2) and (iv) at resistance to further weight loss (plateau). At each phase of the weight-reducing programme, body weight and composition as well as RMR were measured. A regression equation was established in a control population of the same age to predict RMR in obese men at each phase of the weight-loss programme. We observed that body weight and fat mass (FM) were significantly reduced (P < 0.05), while fat-free mass remained unchanged throughout the programme. In phase 1, measured RMR had fallen by 418 kJ/d, more than predicted (P < 0.05), and this difference reached 706 kJ/d at plateau (P < 0.05 v. phase 1). A positive association (r 0.64, P < 0.05) was observed between the reduction in thermogenesis and the degree of FM depletion at plateau. The adaptive reduction in thermogenesis at plateau was substantial and represented 30.9% of the compensation in energy balance that led to resistance to further lose body weight. In conclusion, these results show that adaptive reduction in thermogenesis may contribute to the occurrence of resistance to lose fat in obese men subjected to a weight-reducing programme.