Activated brown adipose tissue and its relationship to adiposity and metabolic markers: an exploratory study

Objective: To explore relationships between PET/CT characteristics of cold-activated brown adipose tissue (BAT), measures of adiposity and metabolic markers.Methods: We conducted a post-hoc analysis of a study which utilized PET/CT to characterize BAT. 25 men ages 18-24 (BMI 19.4 to 35.9 kg/m²) were studied. Fasting blood samples were collected. Body composition was measured using DXA. An individualized cooling protocol was utilized to activate BAT prior to imaging with PET/CT.Results: There was an inverse relationship between fasting serum glucose and BAT volume (r = -0.40, p = 0.048). A marginally significant inverse relationship was also noted between fasting glucose and total BAT activity (r = -0.40, p = 0.05). In addition, a positive correlation was observed between serum FGF21 and SUV_max (r = 0.51, p = 0.01). No significant correlations were noted for measures of BAT activity or volume and other indicators of adiposity or glucose metabolism.Conclusions: The presence of active BAT may be associated with lower fasting glucose in young men. BAT activity may also be correlated with levels of FGF21, suggesting that BAT may lower glucose levels via an FGF21 dependent pathway. Further studies are needed to clarify mechanisms by which BAT may impact glucose metabolism.