Context: Since the discovery of functional brown adipose tissue (BAT) in adult humans, there has been a renewed interest in the physiology of human BAT. Imaging studies from our laboratory and others have shown increased glucose uptake in adipose tissue regions assumed to be BAT in humans. We have also shown that human BAT from the supraclavicular (SCV) region is positive for uncoupling protein-1. To date, however, the oxidative capacity of this adipose tissue (AT) depot has not been characterized in humans.

Objective: We hypothesize that oxidative capacity is increased in the AT of the SCV region known to contain human BAT.

Design: This was an observational prospective cohort study.

Setting: The study was conducted at a referral center.

Patients: Participants were 13 patients for whom thyroid gland surgery was indicated.

Main outcome measure: Basal cellular oxygen consumption in human AT biopsy samples from the SCV region, known to be [¹⁸F]fluorodeoxyglucose positron emission tomography-computed tomography-positive, was compared with the cellular oxygen consumption in subcutaneous white adipose tissue (WAT) from the same region of the same subject.

Results: We show for the first time that AT from the human BAT region displays increased oxygen consumption (P < .05), on average 300% higher, than subcutaneous WAT of the same individual. The contribution of the proton leak to maximal respiration increased with age in the WAT but not in the AT from the BAT region.

Conclusions: These results suggest that human adipose tissue from the BAT region can be distinguished from subcutaneous WAT by a higher basal oxidative capacity. Additional studies are warranted to further elucidate the metabolic and bioenergetic characteristics of this AT depot in humans.