Low glycemic index diet found to decrease insulin sensitivity

A study of overweight and obese adults without diabetes, and with a low glycemic index of dietary carbohydrate, did not have improvements in insulin sensitivity or cardiovascular benefits.
These findings came from a study conducted by Frank M. Sacks, M.D., of Brigham and Women’s Hospital and Harvard Medical School, Boston and colleagues.
Studying the Glycemic Index
The Glycemic Index (GI) ranks carbohydrate-containing food depending on the rate at which the body breaks it down to form glucose.
In the study, 163 overweight adults with pre-hypertension or stage 1 hypertension were given four different diets, each for five weeks, and completed at least two study diets.
The diets were:
High carbohydrate (58% of total energy)/high glycemic index (65 or higher on the glucose scale)
High carbohydrate/low glycemic index (45 or lower on the glucose scale)
Low carbohydrate (40% of energy)/high glycemic index
Low carbohydrate/low glycemic index
None of the participants had diabetes, but 30 per cent had fasting blood glucose levels of 5.6 mmol/l (100 mg/dl) or greater, with each diet rich in fruit, vegetables, low-fat dairy foods and low saturated and total fat.
Unexpected findings
High dietary carbohydrate content was found to decrease insulin sensitivity, while there were no changes in HDL cholesterol or triglyceride level or blood pressure.
“The unexpected findings of the study by Sacks et al suggest that the concept of glycemic index is less important than previously thought, especially in the context of an overall healthy diet, as tested in this study,” said Robert H. Eckel, M.D., of the University of Colorado Anschutz Medical Campus, Aurora.
“These findings should therefore direct attention back to the importance of maintaining an overall heart-healthy lifestyle, including diet pattern.”