Background

Brown adipose tissue (BAT) is present and metabolically active in adult humans. BAT is a key contributor to basal (BEE) and post-prandial energy expenditure (PPEE) in rodents. However, whether this is the case in humans remains unknown.

Methods

A total of 112 young adults (68.8% women; 22.1±2.3 years; 24.5±4.5 Kg/m2) participated in this cross-sectional study. BAT volume and 18F-Fluorodeoxyglucose (18F-FDG) uptake were assessed by a Positron Emission Tomography and Computerized Tomography (PET-CT) static scan, after a two-hour personalized cooling protocol. BEE and PPEE were assessed by indirect calorimetry. BEE was recorded during 30 minutes immediately before the ingestion of a liquid breakfast (milk-shake of mixed composition: 47% CHO, 30% FAT, 15% PRO, 3% FIB) tailored to a quantity equivalent to their 50% of BEE. PPEE was then measured over 3 hours and 20 minutes. BEE was determined as the mean energy expenditure over 5 minutes of stable values whereas PPEE was determined by the energy expenditure area under the curve for the post-prandial period.

Results

BEE was not associated with BAT volume (β=0.51; R2=0.009; P=0.37), 18F-FDG mean uptake (β=-15.96; R2=0.009; P=0.36) or 18F-FDG peak uptake (β=-2.52; R2=0.005; P=0.53). Similarly, we found no association between PPEE and BAT volume (β=0.03; R2=0.056; P=0.07), 18F-FDG mean uptake (β=0.44; R2=0.015; P=0.36) or 18F-FDG peak uptake (β=0.12; R2=0.02; P=0.29). All associations remained not significant after adjusting for potential confounders in the model such as date when the PET-CT was performed, sex, and body mass index.

Conclusions

The results of this study show that BAT is not related with BEE and PPEE in humans. These findings concur with previous studies and provide further evidence indicating that BAT plays a negligible role on energy balance in humans.