The Thermogenic Responses to Overfeeding and Cold Are Differentially Regulated

OBJECTIVE: Brown adipose tissue (BAT) is a highly metabolic tissue that generates heat and is negatively associated with obesity. BAT has been proposed to mediate both cold-induced thermogenesis (CIT) and diet-induced thermogenesis (DIT). We therefore investigated whether there is a relationship between CIT and DIT in humans. METHODS: Nine healthy men (23±3 years old, 23.0±1.8 kg/m(2)) completed 20 minutes of cold exposure (4°C) five days per week for four weeks. Before and after the intervention, CIT (the increase in RMR at 16°C relative to 22°C) was measured by a ventilated hood indirect calorimeter, whereas DIT was measured as the 24-hour thermic response to one day of 50% overfeeding (TEF(150%)) in a respiratory chamber. RESULTS: After the cold intervention, CIT more than doubled from 5.2±14.2% at baseline to 12.0±11.1% (p=0.05), in parallel with increased SNS activity. However, twenty-four-hour energy expenditure (2166±206 vs. 2118±188 kcal/day; p=0.15) and TEF(150%) (7.4±2.7% vs. 7.7±1.6%; p=0.78) were unchanged. Moreover, there was no association between CIT and TEF(150%) at baseline or post-intervention, nor in their changes (p≥0.47). CONCLUSIONS: Cold acclimation resulted in increased CIT but not TEF(150%). Therefore, it is likely that CIT and DIT are mediated by distinct regulatory mechanisms.