Objective: To examine whether fasting insulin concentrations and markers of first-phase insulin secretion are associated with weight gain and changes in distribution of adiposity over 4.4y.
Design: Longitudinal prospective population-based cohort study of middle-aged Caucasians.
Subjects: 767 subjects (40-65y at baseline) were followed up for a mean of 4.4y.
Measurements: 75 g oral glucose tolerance test performed at baseline and follow-up. Insulin was measured at fasting, and 30 and 120 min post-glucose load using a highly specific assay.
Results: Fasting insulin levels were correlated with baseline weight (r = 0.32, P<0.001), as was the 30 min insulin incremental response (r = 0.17, P<0.001). Mean weight gain over the 4.4y of follow-up was 2.17 kg (range: -6.17-10.5 kg) for men and 2.49 kg (range: -7.41-12.39 kg) for women. In women, the 30 min insulin incremental response was negatively associated with percentage weight gain (P<0.001), but there was no relationship between fasting insulin levels and weight gain. The baseline fasting insulin was positively correlated with percentage increase in waist- hip ratio (r = 0.12, P = 0.01). In stratified analysis, this relationship was confined to women over the age of 50 y. However, in men, none of these relationships were demonstrable.
Conclusion: In middle-aged women reduced first-phase insulin secretion was associated with an increased risk of future weight gain, whereas fasting hyperinsulinaemia was associated with an increase in waist-hip ratio over time.