Reducing the glycemic load (GL) is considered beneficial for managing insulin resistance. The GL can be reduced either by reducing carbohydrate intake or by reducing the glycemic index (GI). We studied whether these 2 dietary maneuvers have the same long-term effects on postprandial plasma glucose, insulin, triacylglycerol, and free fatty acid (FFA) concentrations in subjects with impaired glucose tolerance (IGT). Thirty-four subjects with IGT were randomly assigned to high-carbohydrate, high-GI (high-GI); high-carbohydrate, low-GI (low-GI); and low-carbohydrate, high-monounsaturated fatty acid (MUFA) diets for 4 mo. Plasma glucose, insulin, and FFAs were measured from 0800 to 1600 at baseline in response to high-GI meals (60% carbohydrate, GI = 61, GL = 63) and after 4 mo in response to meals representative of the study diet. Carbohydrate intake (% of energy), GI, and GL in the high-GI, low-GI, and MUFA groups (breakfast and lunch meals combined), respectively, were 60%, 61, and 63; 60%, 53, and 55; and 49%, 61, and 52. Compared with the change after 4 mo of the high-GI diet, both the low-GI and MUFA diets reduced 0-8-h mean plasma glucose concentrations by 0.35 mmol/L (P < 0.05). Mean plasma insulin was approximately 20% higher (P < 0.05) and FFAs approximately 12% lower (P < 0.05) after the low-GI diet than after the high-GI diet, with no significant effect of MUFA. Changes in 0-8-h mean plasma triacylglycerols in the 3 treatment groups differed significantly: -0.14, 0.04, and 0.18 mmol/L, respectively, with the high-GI, MUFA, and low-GI diets. In subjects with IGT, reducing the GI of the diet for 4 mo reduced postprandial plasma glucose by the same amount as did reducing carbohydrate intake. The 2 dietary maneuvers had different effects on postprandial plasma insulin, triacylglycerols, and FFAs.
