A.C. McMillan & M. D. White

Simon Fraser University, Burnaby, BC, CANADA

The hypothesis of adaptive thermogenesis suggests obese relative to non-obese humans have reduced metabolic responses to daily physical stresses such as cold exposure. This predisposes obese to a positive energy balance making it more difficult for them to achieve a healthy body weight. PURPOSE/HYPOTHESIS: It was hypothesized that the obese would have a smaller metabolic response to surface cooling relative to the non-obese. METHODS: Three non-obese males (age: 31.3 ± 11.2 years, weight: 72.8 ± 10.7 kg, height: 1.79 ± 0.07 m, BMI: 22.6 ± 2.5 kg/m2; mean ± SD) and 3 obese males (age: 31.3 ± 12.7 years, weight: 110.9 ± 15.9 kg, height: 1.76 ± 0.09 m, BMI 35.7 ± 2.0 kg/m2) volunteered for the study that was approved by the SFU Office of Research Ethics. Oxygen consumption (VO2, ml/min/kg, STPD) was measured by indirect calorimetry. Rectal temperature (Tre, °C) and mean skin temperature (Tsk, posterior shoulder, arm, thorax, abdomen and thigh) were measured with calibrated thermocouples. Each volunteer participated in 3 trials on 3 separate days and each trial began after an overnight fast. Wearing only shorts, the volunteer was seated in a climatic chamber and exposed to 1 of 3 ambient temperatures: Trial 1) 26°C for 90 min, Trial 2) 26°C for 40 min, followed by 90 min at 18°C and Trial 3) 26°C for 40 min, followed by 90 min at 10°C. RESULTS: In the 3 conditions Tre in both groups was ~ 36.7±0.2°C during the final 20 min of each exposure. After ~70 min at 26, 18 and 10°C mean Tsk stabilized at 3 significantly different levels (p

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