Individual thermogenic responses to mild cold and overfeeding are closely related

Context: Adaptive thermogenesis is defined as the increase in energy expenditure in response to overfeeding or cold. Large interindividual differences in adaptive thermogenesis have been described. Objective: Because there are indications for a common underlying mechanism, we studied in humans whether the increase in thermogenesis during short-term overfeeding ( 3 d) is related to mild cold-induced thermogenesis. Interventions: Thirteen lean male subjects have been exposed to three experimental conditions in respiration chambers: baseline ( 36 h in energy balance at thermoneutrality, 22 C), overfeeding ( 84 h at 160% of energy balance, 22 C), and mild cold ( 84 h in energy balance, 16 C). Main Outcome Measures: During the interventions, total daily energy expenditure ( TDEE), physical activity, skin temperatures, and core temperature were measured. After each condition, fasting plasma norepinephrine concentration was measured. Results: Overfeeding caused significant increases in TDEE ( 0.77 MJ/d, P < 0.001). During cold exposure TDEE increased significantly ( 0.59 MJ/d, P < 0.005), whereas physical activity decreased. The changes in TDEE during both overfeeding and mild cold exposure showed considerable interindividual variation ( respectively, -0.11 to 1.61 MJ/d and -0.19 to 1.58 MJ/d). The individual changes in energy expenditure during mild cold exposure and overfeeding were highly correlated ( P < 0.005). Fasting norepinephrine plasma concentrations correlated significantly to energy expenditure in both situations ( P < 0.05). Conclusions: These results suggest that both overfeeding-induced and mild cold-induced adaptive thermogenesis share common regulating mechanisms. This indicates that cold exposure could be used as a biomarker for the individual thermogenic response to excess energy intake.