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Article Title

NON-SHIVERING THERMOGENESIS RESPONSES TO ACUTE MILD COLD EXPOSURE IN OBESE AND NON-OBESE INDIVIDUALS

Abstract

INTRODUCTION: In response to mild cold exposure, brown adipose tissue (BAT) produces heat via non-shivering thermogenesis (NST). It has been suggested that individuals with a greater BAT capacity may be better able to maintain their body weight. Forward Looking InfraRed (FLIR) cameras have been employed to assess temperatures in the supraclavicular regions where larger BAT depots are located in humans. PURPOSE/HYPOTHESIS: For healthy college-aged males it was hypothesised that obese relative to non-obese would have smaller metabolic and NST responses to acute mild cold exposure. METHODS: Eight college-aged non-obese males with 16.23 % percent body fat (BF) and 8 obese males with 30.88 % BF volunteered for the study that was approved by the SFU Office of Research Ethics. Oxygen consumption (VO2, mL/min/kg body weight) was measured by indirect calorimetry with a pre-calibrated metabolic cart and rectal temperature (TRE,°C) with calibrated thermistors. Surface heat flux (HF, W m-2) and skin temperature (TSK­,°C) were measured with calibrated heat flux discs on 7 body surface sites including the right and left supraclavicular areas, chest, posterior shoulder, upper arm, abdomen and thigh. After an overnight fast each volunteer, wearing only shorts, sat in a climatic chamber at 26°C for 90 min and then for 90 min at 19°C. RESULTS: The TRE in both groups remained at ~36.86±0.48 during each exposure. At 19°C the obese had a lower mean TSK of 29.12±0.38°C relative to the non-obese mean TSK 30.72±0.63°C (p < 0.05), a lower mean HF of 80.46±7.03 W m-2 relative to that of 97.50±6.15 W m-2 (p < 0.05) for the non-obese and a lower mean VO2 of 2.58±0.55m L/min/kg (p<0.05) relative to that of 4.16±0.57 mL/min/kg in the non-obese. Heat flux over the supraclavicular BAT depots was 84.01±18.49 W m-2 in the obese and this was lower (p < 0.05) than that of 113.93±15.39 W m-2 in the non-obese. At this same site the obese supraclavicular TSK of 30.70±0.53°C was lower than that of 32.66±0.73 ( p<0.05) for the non-obese. This was further confirmed by FLIR imaging of the supraclavicular regions. CONCLUSION: Obese individuals appear to have lower non-shivering thermogenesis relative to non-obese and this suggests they have a lower BAT activation during mild acute cold exposure.

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