Brown Adipose Tissue: A Protective Mechanism Against "Preprediabetes"?

Brown adipose tissue (BAT) is present in a significant number of adult humans and has been postulated to exert beneficial metabolic effects. Lean, nondiabetic patients undergoing clinical PET/CT imaging are more likely to exhibit incidental BAT activation. The aim of this study was to assess metabolic changes associated with the cold activation of BAT and to compare baseline blood metabolites in participants with varying amounts of active BAT. Methods: Serum blood samples were collected from healthy adult volunteers (body mass index, 18.0-25.0, and age ≤ 35 y) before and after 2 h of exposure to cold. 18F-FDG PET/CT imaging was performed immediately after cold exposure. Activated BAT was segmented, and fasting glucose, insulin, lipid, and other blood metabolite levels were correlated with volume and intensity of active BAT. Using a median cutoff, subjects were classified as high-BAT (BAThigh) or low-BAT (BATlow). Results: A higher volume of activated BAT was associated with significantly higher precooling glucose and insulin levels (P < 0.001 for each). Precooling thyroid-stimulating hormone and triglyceride levels were significantly higher in the BAThigh than the BATlow group (P = 0.002 and P < 0.001, respectively). Triglyceride levels tended to increase over the cooling period in both BAT groups but increased significantly more in the BAThigh group (15.7 ± 13.2 mg/dL; P < 0.001) than in the BATlow group (4.5 ± 12.2 mg/dL; P = 0.061). Conclusion: These findings may indicate that BAT is recruited to counteract incipient "preprediabetic" states, potentially serving as a first-line protective mechanism against very early metabolic or hormonal variations.