Abstract
CONTEXT: Metabolic flexibility reflects the ability to switch from lipid to carbohydrate oxidation during insulin stimulation manifested in increased respiratory quotient (RQ). Little is known about adipose tissue metabolism and metabolic flexibility in adolescent girls with polycystic ovary syndrome (PCOS). OBJECTIVE: We investigated whole-body lipolysis, substrate oxidation, and metabolic flexibility in obese girls with PCOS vs obese girls without PCOS. PATIENTS/DESIGN: Twenty-one obese girls with PCOS and 21 obese girls without PCOS were pair-matched for age and race. Body composition, abdominal visceral adipose tissue (VAT), sex hormones, lipid profile, and adiponectin were measured. Whole-body lipolysis ([2H5]glycerol turnover), RQ, and substrate oxidation (indirect calorimetry) were evaluated during fasting and a hyperinsulinemic-euglycemic clamp together with assessment of insulin sensitivity (IS). RESULTS: Despite similar body mass index and percent body fat, girls with PCOS vs girls without PCOS had lower fasting lipolysis and fat oxidation, less increase in RQ during hyperinsulinemia with impaired suppression in lipolysis and lipid oxidation, and lower IS. In multiple regression, the best predictors of metabolic flexibility were [using clinical parameters: adiponectin, fasting triglycerides, and insulin (R2 = 0.618, P < 0.0001); using research parameters: IS, VAT, and baseline RQ (R2 = 0.756, P < 0.0001)]. CONCLUSIONS: Obese girls with PCOS vs obese girls without PCOS have decreased lipid mobilization, diminished fat oxidation, and metabolic inflexibility. Whether this metabolic phenotype of adipose tissue dysfunction, which is conducive to fat accretion, plays a role in the induction and maintenance of obesity in adolescent girls with PCOS remains to be determined.