Issue 147 Item 12 Ways Of Reducing Glycemic Load Vary In Effects

Three diets studied, high carbs with high glycemic index, high carbs with low glycemic index and low carbs and high monounsaturated fatty acid. Reduction in either dietary carbohydrate or glycemic index reduces postprandial plasma glucose equally in patients with impaired glucose tolerance, although the two approaches vary in their effects.

While both are beneficial for managing insulin because they reduce the glycemic load, they influence postprandial plasma insulin, triacylglycerols and free fatty acids differently, say specialists at the University of Toronto and St. Michael’s Hospital, Toronto, Canada. The researchers studied the effects of the two approaches in 34 patients with impaired glucose tolerance.

The patients were randomized to three different diets over four months: one high in carbohydrate with high glycemic index, another high in carbohydrate with low glycemic index and the third low in carbohydrate and high in monounsaturated fatty acid.

Plasma glucose, insulin and free fatty acids were measured from 0800 to 1600 hours at baseline in response to high glycemic index meals (60% carbohydrate, with glycemic index of 61 and glycemic load of 63). Their responses to the study diets (breakfast and lunch combined) were measured four months later.

In the high glycemic index group, carbohydrate intake (percent of energy) was 60%, glycemic index 61 and glycemic load 63. In the low glycemic index group, carbohydrate intake was 60%, glycemic index 53 and glycemic load 55. In the monounsaturated fatty acid group, carbohydrate intake was 49%, glycemic index 61 and glycemic load 52.

Compared to the change with the high glycemic index diet, the other two diets reduced 0 to 8 hour mean plasma glucose concentrations by 0.35 mmol/litre.

Mean plasma insulin was about 20% higher and free fatty acids about 12% lower after the low glycemic index diet than after the high glycemic index diet. These changes were statistically significant but there was no significant effect with monounsaturated fatty acid.

Changes in 0 to 8 hour mean plasma triacylglycerols in the three groups did differ significantly. They were -0.14 mmol/litre with the high glycemic index diet, 0.04 mmol/litre with the monounsaturated fatty acid diet and 0.18 mmol/litre with the low glycemic index diet. American Journal of Clinical Nutrition 2003;77:3:612-621.