High-Carb, Low-GI Diet Holds Benefits

A diet that is both high in protein and has a low glycemic index (GI) increases body-fat loss, but cardiovascular risk reduction is optimized by a high-carbohydrate, low-GI diet, according to a new study by researchers from the University of Sydney, Macquarie University and Royal Prince Alfred Hospital, all of Sydney, Australia. The results of the study were published as "Comparison of Four Diets of Varying Glycemic Load on Weight Loss and Cardiovascular Risk Reduction in Overweight and Obese Young Adults" in the July 24 edition of the Archives of Internal Medicine (see http://archinte.ama-assn.org/cgi/content/abstract/166/14/1466).

The researchers--Joanna McMillan-Price; Peter Petocz, Ph.D.; Fiona Atkinson; Kathleen O'Neill; Samir Samman, Ph.D.; Dr. Katherine Steinbeck; Dr. Ian Caterson; and Jennie Brand-Miller, Ph.D.--sought to investigate the effects of a low-GI, high-protein diet on weight loss and cardiovascular risk. The study involved assigning 129 overweight or obese young adults to one of four reduced-fat, high-fiber diets for 12 weeks. Diets one and two were high-carbohydrate (55% of total energy intake), with high and low GIs, respectively. Diets three and four were high-protein (25% of total energy intake), with high and low GIs, respectively. The glycemic load was highest in diet one and lowest in diet four. The researchers then studied changes in weight, body composition and blood chemistry.

Results showed that while all groups lost a similar percentage of weight, the proportion of subjects in each group who lost 5% or more of body weight varied significantly by diet. Women on diets two and three lost approximately 80% more fat mass than those on diet one. Mean low-density-lipoprotein (LDL) cholesterol levels declined significantly in diet two, but increased in diet three. This led the researchers to conclude that high-protein and low-GI regimens increase body fat loss, but cardiovascular risk reduction is optimized by a high-carbohydrate, low-GI diet.

In the Archives of Internal Medicine article, the authors note, "Moderate reductions in glycemic load appear to increase the rate of body-fat loss, particularly in women." The researchers go on to state that diets based on low-GI whole-grain products--as opposed to high-GI whole-grain products--maximize cardiovascular risk reduction, particularly in combination with high protein intake.