Two Studies Cast Further Doubt on the Effectiveness of Low GI/GL Diets for Weight Loss

12/02/08 A study published in the September 2007 issue of the American Journal of Clinical Nutrition provides further evidence that the glycemic index (GI) of a diet is not important; when it comes to weight loss it is calories that count. This study adds to the growing body of evidence supporting the health benefits of a diet rich in fruits and vegetables, including potatoes, according to the United States Potato Board.

Researchers from Harvard and the State University of Rio de Janeiro in Brazil who worked independently from any food industry sponsors, sought to determine if a low GI diet would be more effective than a high GI diet for long-term weight loss in 203 overweight and obese women. Both diets included a mild energy restriction (i.e., 100-300 fewer calories per day) and had similar macronutrient distributions (i.e., carbohydrate, protein and fat); all that distinguished the two diets were the GIs of the foods. The high GI diet contained a hefty dose of potatoes and other commonly identified high GI foods (e.g., bananas, watermelon, rice and white bread) while the low GI diet contained large amounts of beans and other low GI foods (e.g., apples, pears, oats, and sweet potatoes). At the end of the 18-month period both groups had lost weight and there were no significant differences in weight loss between the two groups.

The results are timely for America's favorite vegetable, the potato, and the U.S. potato industry, which has been unfairly maligned by low GI diets. Far from a dietary villain, potatoes are a satiating and nutrient rich vegetable containing 45% of the recommended daily value (DV) of vitamin C, 18% DV of potassium*, and no fat, sodium, or cholesterol -- all for 110 calories per 5.3 ounce serving.

Another study published last spring in the American Journal of Clinical Nutrition conducted by the Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging at Tufts University (USDA HNRCA) also showed that the glycemic load of the diet doesn't matter as long as calories are reduced. In this study, 34 overweight, but otherwise healthy, men and women achieved and maintained similar weight and body fat losses after one year, whether they were on a low-glycemic-load or a high-glycemic-load diet. The reason? Both groups reduced their energy intake by 30%.

According to Glenn Gasser, Associate Professor of Exercise Physiology at the University of Virginia, the results of these studies are not surprising. "If you want to lose weight reduce the number of calories you consume, not carbohydrates!" In a recent review published in the Journal of the American Dietetic Association, Gasser found that diets high in carbohydrates are almost universally associated with slimmer bodies and consuming a high-glycemic diet is not associated with higher body weights. "It is not the GI or GL that makes for healthier bodies, but the overall quality of a high-carb diet, which includes more fiber-rich and nutrient dense foods. Potatoes can certainly fit into this category."