By Thomas S. May
BUDAPEST, HUNGARY -- April 24, 2007 -- Switching to a low glycaemic index (GI) diet from a high GI diet can result in improvements in insulin sensitivity, and may thereby lower the risk of type 2 diabetes in overweight or obese individuals with impaired glucose tolerance, according to a controlled, 24-week, crossover study presented here at the 15th European Congress on Obesity (ECO).
There is increasing evidence that habitual consumption of carbohydrates with a high GI (i.e., carbohydrates that are quickly and easily absorbed by the body) contributes to the overall burden of obesity and insulin resistance, which may eventually lead to the development of type 2 diabetes.
Past research using observational methodology has revealed positive correlations between high GI diets and metabolic disorders, but no clear association could be identified by interventional studies so far.
However, in a recent study, led by Louise Aston, PhD, a research scientist with the Nutrition & Health Research Group, MRC Human Nutrition Research Elsie Widdowson Laboratory, in Cambridge, UK, investigators found that replacing foods containing carbohydrates with a high GI (i.e., white bread, white rice, and potatoes) with low GI versions (i.e., whole wheat bread, brown rice) can lead to an improvement in insulin sensitivity, and thus may prevent or delay the development of type 2 diabetes.
Dr. Aston and colleagues enrolled 19 overweight or obese, moderately hyperinsulinaemic women in a crossover study of dietary intervention.
The dietary intervention used in the study was substitutions of like-for-like foods (low or high glycaemic index versions of breads, breakfast cereals and rice, plus potatoes on the high GI diet and pasta on the low GI diet). This meant that the glycaemic index difference between the diets was smaller than in previous studies, but that the intervention was more representative of habitual diets, and more readily achievable and sustainable by patients in the long term, Dr. Aston said.
Another important difference between the present study and previous work in this area was that a novel and highly sensitive method was used to measure insulin sensitivity (an orally-stimulated intravenous glucose tolerance test), she said, enabling the detection of small but potentially clinically important differences in insulin sensitivity between treatments.
The researchers measured insulin sensitivity at baseline and after 12 weeks of either high or low GI diets. GI values of intervention foods differed by a mean of 28.5 units for equivalent low and high GI foods (P <.05).
Results show that insulin sensitivity was one third higher following the low GI diet than following the high GI diet (P =.05), and the 15-minute insulin increment following oral glucose was 25% higher after the low than after the high GI diet (P =.02).
These results demonstrate that switching to a low GI diet can result in improvements in insulin sensitivity and secretion in overweight, hyperinsulinaemic women, Dr. Aston said.
"It is likely that this would reduce the risk of developing type 2 diabetes in this group of subjects," she said. "The implication for clinicians, therefore, is that recommending a low GI diet to such patients may reduce their risk of going on to develop type 2 diabetes."
Funding for the study was provided by the UK Medical Research Council.
[Presentation title: Effect of a Low Glycaemic Index Diet on Insulin Sensitivity in Overweight Women. Abstract T3:OS1.5]
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