Background: Low circulating sex hormone-binding globulin (SHBG) concentrations have been associated with the presence of several features of the metabolic syndrome in both men and women. Nutritional factors including dietary lipids and fibers in particular have been suggested to modulate plasma SHBG levels.
Methods: The primary objective of the present study was to investigate the effect of an oat bran-rich supplement in conjunction with the National Cholesterol Education Program(NCEP) Step 1 diet (< 30% of total energy from fat, < 10% of energy from saturated fat, and< 300 mg cholesterol per day) on plasma SHBG levels in 35 overweight premenopausal women. Subjects (age 38.6 ± 7.4 years) had normal menstrual cycles and were tested in the midluteal phase. Since no effect of the oat bran supplement was observed on plasma SHBG levels, data were analyzed according to the 6-week NCEP Step 1 diet.
Results: The NCEP Step 1 nutritional intervention caused a significant decrease in energy intake( –11%, p < 0.05), percent fat intake (–10%, p < 0.005), as well as saturated (–20%, p < 0.005) and monounsaturated (–10%, p < 0.05) fatty acid intake. Body mass index (BMI) decreased slightly but significantly (from 29.2 ± 4.5 to 28.8 ± 4.3 kg/m2, p < 0.005). Plasma SHBG levels increased significantly (from 70.6 ± 17.7 to 79.9 ± 15.3 pmol/L, p < 0.0005) following the 6-week NCEP Step 1 diet, whereas plasma insulin levels were not modified significantly. Significant correlations were observed between the change in plasma SHBG levels and baseline BMI (r = 0.36, p < 0.04), as well as baseline (r = –0.42, p < 0.05) and postintervention (r = –0.35, p < 0.05) HDL cholesterol levels.
Conclusions: We observed that a 6-week NCEP Step 1 diet significantly increased plasma SHBG levels, despite the finding that fasting insulin was not modified. Further studies are needed to elucidate physiological mechanisms underlying a direct effect of dietary composition on SHBG production by the liver.
