Lean Group (N = 10)
Overweight or Obese Group (N =14)
P Value, Lean vs. Obese
P Value, 22°C vs. 16°C
BAT activity (kBq)† BAT volume (cm3)† Resting metabolic rate (MJ/24 hr)
Overweight or Obese Subjects
Thermoneutral conditions Cold exposure Respiratory quotient (VCO2/VO2)‡
Gradient, core and skin Thermoneutral conditions Cold exposure Gradient, arm–finger Thermoneutral conditions Cold exposure
Plus–minus values are means ±SD. BAT denotes brown adipose tissue, VCO2 volume of carbon dioxide produced, and VO2 volume of oxy
BAT activity and BAT volume were measured after cold exposure.
Both VCO2 and VO2 are measured in liters per minute.
T h e ne w engl a nd jour na l o f medicine
Table 2. Activity and Volume of Brown Adipose Tissue, Resting Metabolic Rate Adjusted for Fat-free Mass and Body Temperature under Thermoneutral Conditions (22°C) and after 2 Hours of Cold Exposure (16°C).*
Body temperature (°C) Core
tissue tended to be lower in the overweight or obese subjects than in the lean subjects, but the difference was not significant (P=0.14). Only one subject had no 18F-FDG uptake in areas of adi- pose tissue. This subject had the highest BMI (38.7) and percentage of body fat (41.8%). In all subjects with brown-adipose-tissue activity, the area with the most evidence of activity was the supraclavicular region (Fig. 1). However, other sites also had substantial putative brown-adipose- tissue activity.
and 0 kBq in thermoneutral conditions, in Sub- ject 3 at 587.2 kBq during cold exposure and 0 kBq in thermoneutral conditions, and in Subject 4 at 250.0 kBq during cold exposure and 0 kBq ther- moneutral conditions.
Studies of brown adipose tissue obtained from the supraclavicular region during surgery in the patient with multinodular goiter revealed the pres- ence of UCP1 (Fig. 2). The protein was not detect- ed in white adipose tissue taken from the same region in this patient.
There was no detectable brown-adipose-tissue activity in the three subjects who were retested under thermoneutral conditions (Fig. 1E). Brown- adipose-tissue activity was recorded in Subject 2 (Fig. 1A) at 856.5 kBq during exposure to cold
On exposure to cold, all subjects had an insu- lative response (a reduction of skin temperature relative to core temperature) and a metabolic re- sponse (an increase in heat production) (Table 2). Body core temperature increased slightly in re-
n engl j med 360;15
april 9, 2009
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