Objective: To investigate whether long-term weight fluctuation is associated with the fasting serum insulin concentration.
Design and subjects: Weight histories of 1932 male Japanese workers aged 40-59 y were analyzed in relation to their current fasting serum insulin concentration.
Measurements: Individual weight fluctuation was calculated by root mean square error (RMSE) along the linear regression line of weight measured at five to six different ages.
Results: The mean RMSE and fasting insulin concentration were 1.22 kg and 4.5 microU/ml, respectively. The multivariate adjusted insulin level became higher with the increase in weight fluctuation. Subanalysis stratified by current body mass index (BMI) showed that the multivariate adjusted insulin level in individuals in the top quartile of fluctuation was 4.3 microU/ml, against 3.9 microU/ml in those in the bottom quartile (P=0.018, analysis of covariance (ANCOVA)) in the normal weight subgroup with current BMI below 25 kg/m(2). In the overweight subgroup with BMI 25 kg/m(2) or above, the level was 6.9 microU/ml in individuals in the top quartile and 6.2 microU/ml in those in the bottom quartile (P=0.054, ANCOVA).
Conclusion: The results suggest that weight fluctuation increases the risk of developing hyperinsulinemia. Prospective observations together with measurement of changes in adiposity are needed for confirmation.