Postprandial thermogenesis is reduced in polycystic ovary syndrome and is associated with increased insulin resistance

OBJECTIVE: In order to investigate the possible causes and effects of obesity in polycystic ovary syndrome resting energy expenditure, postprandial thermogenesis and insulin resistance were measured in 14 polycystic ovary syndrome subjects and in 14 controls. DESIGN: A cross-sectional study of a selected group of patients was performed. PATIENTS: Seven of the PCOS subjects were obese and seven lean. Controls were individually matched for age, race, weight, body mass index (BMI) lean body mass and percentage fat. The obese, but not lean, polycystic ovary syndrome subjects had a greater waist:hip ratio than controls (median (range) obese PCOS 0.865 (0.823-0.960) vs obese control 0.804 (0.823-0.940), P less than 0.025). MEASUREMENTS: Metabolic rate was measured by continuous indirect calorimetry and insulin sensitivity was assessed by a short insulin tolerance test. RESULTS: The resting energy expenditure (REE) was similar in PCOS subjects and controls (median (range), 6796 (5489-7774) vs 6833 (4893-8492) kJ/day). REE correlated with LBM in the PCOS group (r = 0.83, P less than 0.00) and the control group (r = 0.82, P less than 0.001). Postprandial thermogenesis was reduced in polycystic ovary syndrome (obese: median 45.4 (range 33.6-100.0) vs 86.5 (67.2-109.2) kJ (P less than 0.05); lean: 79.4 (73.5-108.4) vs 89.9 (76.0-109.2) kJ (P less than 0.05). Fasting insulin (9.7 +/- 3.6 vs 4.4 +/- 0.8 mU/l, P less than 0.05) and postprandial incremental insulin rise (163 +/- 31 vs 116 +/- 15 mU/l, P less than 0.025) were higher in polycystic ovary syndrome. Insulin sensitivity was reduced in polycystic ovary syndrome (obese: median 136 (range 92-169) vs 173 (109-225) mumol/l/min (P less than 0.05); lean: 161 (138-225) vs 194 (161-253) mumol/l/min (P less than 0.05)). The reduction in insulin sensitivity correlated with the reduced postprandial thermogenesis in the polycystic ovary syndrome group (r = 0.75, P less than 0.01). CONCLUSION: These results confirm previous reports of hyperinsulinaemia and insulin resistance in polycystic ovary syndrome. Furthermore, polycystic ovary syndrome subjects have a reduced postprandial thermogenesis which is related statistically to the reduced insulin sensitivity. The decreased postprandial thermogenesis may predispose women with polycystic ovary syndrome to weight gain.