Clinical trials of low-fat diets characteristically produce small mean long-term weight loss but a large interindividual variation in response. This variation has been attributed to psychological and behavioral factors, although biological differences may also play a role.
The objective was to determine whether physiologic differences in insulin secretion explain differences in weight gain among individuals consuming low- and high-fat diets.
Of 276 individuals followed in the Quebec Family Study for a mean of 6 y, we compared those in the lowest with those in the highest dietary fat tertiles. We performed oral-glucose-tolerance tests at baseline and examined the insulin concentration at 30 min (insulin-30) as a proxy measure of insulin secretion. Six-year changes in body weight and waist circumference were the primary endpoints. We determined the associations between insulin-30 and the primary endpoints by linear regression analysis, with adjustment for potentially confounding factors.
Mean changes in body weight and waist circumference did not differ significantly between the lowest- and highest-fat diet groups. However, these endpoints were strongly associated with insulin-30, especially among individuals consuming the lowest-fat diet. Insulin-30 at baseline was significantly associated with 6-y weight gain (r = 0.51, P