DIET‐INDUCED CHANGES IN SEX HORMONE BINDING GLOBULIN AND FREE TESTOSTERONE IN WOMEN WITH NORMAL OR POLYCYSTIC OVARIES: CORRELATION WITH SERUM INSULIN AND INSULIN‐LIKE GROWTH FACTOR‐I

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Abstract
The purpose of this study was to investigate the effect of calorie restriction on serum concentrations of sex hormone binding globulin (SHBG) in women with normal or polycystic ovaries (PCO) and to examine the possible role of insulin and insulin-like growth factor-I (IGF-I) in mediating changes in SHBG levels. Six normal subjects with mean (SD) body mass index (BMI) 25.5 (2.2) and five subjects with PCO (BMI 36.1 (3.7)) were studied before and after 2 or (PCO only) 4 weeks of a very low calorie diet (330 kcal/day; Cambridge Diet). In both normal women and patients with PCO there was a twofold increase in SHBG concentrations after 2 weeks and this was sustained in the PCO subjects for a further 2 weeks. The rise in SHBG was accompanied by a fall in free testosterone concentrations. There were parallel changes in serum insulin and IGF-I concentrations which decreased during the diet and there were significant negative correlations of SHBG with insulin in both normal subjects (r =−0.62) and women with PCO (r =−0.60). In addition, serum concentrations of an insulin-dependent small molecular weight (34 kDa) binding protein for IGF-I (IGF-BPI) increased significantly during dieting in both groups and were negatively correlated with serum insulin (controls, r =−0.56; PCO, r =−0.68) and positively correlated with serum SHBG levels (controls, r = 0.69; PCO, r = 0.63). In summary, these data indicate that in both normal subjects and those subjects with PCO, calorie restriction results in a highly significant increase in SHBG concentrations. Data from this study and related experiments in vitro suggest that the changes in SHBG may be mediated by a fall in insulin and/or IGF-I.