Cold-Induced Energy Burn Higher With Brown Fat
People with brown fat burned significantly more calories in response to cold than those without -- another finding that supports the tissue's potential as a target for weight loss, scientists said. After a 90-minute bout of exposure to cold, eight volunteers with brown fat burned 15% more calories, or an extra 20 kilocalories per day, than age- and weight-matched volunteers without brown fat.

The volunteers with brown fat also had a unique polyunsaturated fatty acid (PUFA) and oxylipin profile with potentially anti-inflammatory and metabolically favorable characteristics. In addition, those with brown fat had higher circulating levels of various lipids, including the brown fat-derived lipokines diHOME and 12-HEPE, in response to cold.

The study included 16 healthy volunteers matched by age and body mass index (BMI) who had been previously identified as BAT-positive or -negative in a cross-sectional imaging study. There were eight participants in each group, all of whom underwent an initial positron emission tomography/computed tomography (PET/CT) scan at room temperature (23°C) to detect any basal BAT activity. After that, the participants underwent indirect calorimetry examinations before, during, and after 90 minutes of cold exposure to assess the magnitude and duration of cold-induced energy expenditure.

The cold challenge was done with a water-perfused cooling vest, with the water kept slightly above the shivering temperature. After the challenge, as participants warmed up, indirect calorimetry measurements were repeated every hour until energy expenditure returned to baseline levels. Blood was taken before and after the cold exposure for laboratory analysis.