Comparison of the effects of sucrose and fructose on insulin action and glucose tolerance

The purpose of the present study was to determine whether fructose is the nutrient mediator of sucrose-induced insulin resistance and glucose intolerance. Toward this end, male rats were fed a purified starch diet (68% of total calories) for a 2-wk baseline period. After this, rats either remained on the starch (ST) diet or were switched to a sucrose (SU, 68% of total calories), fructose/glucose (F/G, 34/34% of total calories), or fructose/starch (F/ST, 34/34% of total calories) diet for 5 wk. Rats then underwent either an intravenous glucose tolerance test (n = 10/diet) or a euglycemic, hyperinsulinemic clamp (n = 8 or 9/diet). Incremental glucose and insulin areas under the curve in SU, F/G, and F/ST were on average 61 and 29% greater than ST, respectively, but not significantly different from one another. During clamps, glucose infusion rates (mg·kg^-1·min^-1) required to maintain euglycemia were significantly lower (P < 0.05) in SU, F/G, and F/ST (13.4 ± 0.9, 9.5 ± 1.7, 11.3 ± 1.3, respectively) compared with ST (22.8 ± 1.1). Insulin suppression of glucose appearance (mg·kg^-1·min^-1) was significantly lower (P < 0.05) in SU, F/G, and F/ST (5.6 ± 0.5, 2.2 ± 1.2, and 6.6 ± 0.7, respectively) compared with ST (9.6 ± 0.4). Insulin-stimulated glucose disappearance (mg·kg^-1·min^-1) was significantly lower (P < 0.05) in SU, F/G, and F/ST (17.9 ± 0.6, 16.2 ± 1.3, 15.3 ± 1.8, respectively) compared with ST (24.7 ± 1.2). These data suggest that fructose is the primary nutrient mediator of sucrose-induced insulin resistance and glucose intolerance.