Long-term effect of varying the source or amount of dietary carbohydrate on postprandial plasma glucose, insulin, triacylglycerol, and free fatty acid concentrations in subjects with impaired glucose tolerance

Background: 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). Objective: 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 wit h impaired glucose tolerance (IGT). Design: 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. Results: 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 approximate to 20% higher (P < 0.05) and FFAs approximate to12% 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. Conclusions: 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.