Poster Topical Area: Energy and Macronutrient Metabolism
Location: Hall D
Poster Board Number: 483
When ambient temperature decreases beyond the thermoneutral zone, heat generation and a concomitant increase in energy expenditure (EE) are required to maintain core temperature. The increase in EE occurs in skeletal muscle, where shivering leads to unsustainable increases in EE, and brown adipose tissue (BAT), where non-shivering thermogenesis (NST) increases EE through prolonged heat production. However, measuring these organs' separate metabolic activity in vivo is challenging.
Objectives: The goal of the present study was to quantify the adaptive increase in whole-body EE as a result of NST in response to mild cold exposure (21ºC) in normal weight and overweight/obese individuals. We hypothesized that EE increases upon mild cold exposure without shivering, suggesting a quantifiable contribution of BAT to EE.
Methods: Whole-body resting EE (REE) was measured at room temperature (24ºC) and mild cold exposure (21ºC) in normal weight (NW; n=10) and healthy overweight/obese (OW; n=6) individuals. Measurements were conducted via indirect calorimetry following a 12-hour fast during two separate visits in random order with diet replication before each visit. Body composition and supraclavicular heat production (SHP), assessed via infrared thermography, were also measured.
Results: NW and OW participants did not differ in age (p=0.31). Per study design, body weight (p<0.001), fat mass (FM; p<0.001), and fat free mass (FFM; p=0.037) were significantly greater among OW when compared to NW. Whole-body REE at 24°C, normalized for FFM, was similar between NW and OW (26.0 ± 0.3 vs. 25.6 ± 0.7 kcal/kg FFM; p=0.86). At 21°C, REE increased in both NW (+5.7 ± 0.5%, p=0.002) and OW (+10.7 ± 2.0%, p=0.037), but the increase in REE was not significantly different between OW and NW (p=0.37). When compared to 24°C, SHP at 21°C increased to a similar extent in both NW (+1.2 ± 0.2°C, p=0.03) and OW (+1.4 ± 0.1°C; p<0.001).
Conclusions: NST is inducible upon mild cold exposure to a similar extent in both NW and healthy OW individuals and occurs with a concomitant increase in SHP, possibly reflecting BAT activity. This suggests that mild cold exposure may be a practical method to quantify acute BAT activity in terms of kilocalorie expenditure.
University of Nebraska-Lincoln