Obesity is associated with increasing cardiometabolic morbidity and mortality rates worldwide. Not everyone with obesity, however, develops metabolic complications. Brown adipose tissue (BAT) has been suggested to be a promoter of leanness and metabolic health. To date, little is known about the prevalence and metabolic function of BAT in people with severe obesity, a population at high cardiometabolic risk. In this cross-sectional study, we included 40 individuals with World Health Organization class II-III obesity (BMI ≥35 kg/m2). Using a 150-min personalized cooling protocol and 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography, cold-activated BAT was detectable in 14 of the participants (35%). Cold-induced thermogenesis was significantly higher in participants with detectable BAT compared with those without. Notably, individuals with obesity and active BAT had 28.8% lower visceral fat mass despite slightly higher total fat mass compared with those without detectable BAT 18F-FDG uptake. The lower amount of visceral fat mass was accompanied by lower insulin resistance and systemic inflammation and improved nonalcoholic fatty liver disease parameters, all adjusted for age, sex, and percent body fat. Contrary to previous assumptions, we show here that a significant fraction of individuals with severe obesity has active BAT. We found that decreased BAT 18F-FDG uptake was not associated with adiposity per se but with higher visceral fat mass. In summary, active BAT is linked to a healthier metabolic phenotype in obesity.

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Due to its high metabolic activity, brown adipose tissue (BAT) has become a promising target for the development of novel treatment concepts for metabolic disease. Despite several reports of a negative association between the presence of active BAT and obesity, very little is known about the quantitative and qualitative differences of BAT in lean and obese individuals. Systematic studies directly comparing cold-induced BAT activity in leanness and obesity are currently lacking. Here we studied BAT mass and function in 31 lean and 64 obese men and women. After a standardized cooling protocol using a water-perfused vest, 18F-FDG-positron emission tomography/computed tomography scans were performed, and BAT was delineated using lean body-mass adjusted standardized uptake value (SUV) thresholds in anatomic regions with fat radiodensity. Cold-induced thermogenesis (CIT), a functional readout of BAT activity, was quantified by indirect calorimetry. Active BAT was present in a significantly higher proportion of lean than obese individuals (58% vs. 33%, p=0.019). In these participants with active BAT, however, BAT volume and activity did not differ between leanness and obesity. Accordingly, CIT was similar in both weight groups. BAT metrics were not related to adiposity or total fat mass per se. However, in obese participants a strong negative correlation existed between visceral adipose tissue and BAT volume, 18F-FDG uptake and CIT. In summary, despite a significantly lower prevalence of BAT, the metabolic activity and thermogenic capacity of BAT appears to be still intact in obesity and is inversely associated with visceral fat mass.

Obesity is associated with increasing cardiometabolic morbidity and mortality worldwide. Not everyone with obesity, however, develops metabolic complications. Brown adipose tissue (BAT) has been suggested as a promoter of leanness and metabolic health. To date, little is known about the prevalence and metabolic function of BAT in subjects with severe obesity, a population at high cardiometabolic risk. In this cross-sectional study, we included 40 individuals with WHO class II-III obesity (BMI ≥ 35 kg/m²). Employing a 150-minute personalized cooling protocol and ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography, cold-activated BAT was detectable in 14 (35%) of the participants. Cold-induced thermogenesis was significantly higher in participants with detectable BAT compared to those without. Notably, individuals with obesity and active BAT had 28.8% lower visceral fat mass despite slightly higher total fat mass compared to those without detectable BAT ¹⁸F-FDG uptake. This was accompanied by lower insulin resistance and systemic inflammation and improved NAFLD parameters, all adjusted for age, sex, and percent body fat. Contrary to previous assumptions, we show here that a significant fraction of individuals with severe obesity has active BAT. We found that decreased BAT ¹⁸F-FDG uptake was not associated with adiposity per se but with higher visceral fat mass. In summary, active BAT is linked to a healthier metabolic phenotype in obesity.

No abstract