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 n utrient mediator of sucrose-induced insulin resistance and glucose intolera nce. Toward this end, male rats were fed a purified starch diet (68% of tot al calories) for a 2-wk baseline period. After this, rats either remained o n the starch (ST) diet or were switched to a sucrose (SU, 68% of total calo ries), 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, hyper insulinemic 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 tha n ST, respectively, but not significantly different from one another. Durin g clamps, glucose infusion rates (mg.kg(-1).min(-1)) required to maintain e uglycemia 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 sig nificantly 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-sti mulated 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, r espectively) compared with ST (24.7 +/- 1.2). These data suggest that fruct ose is the primary nutrient mediator of sucrose-induced insulin resistance and glucose intolerance.