It was all the rage not long ago.
Diet books like South Beach and Atkins preached the wonders of eating foods low in glycemic load because, the theory went, low-glycemic foods kept your blood sugars down. Conversely, high-glycemic foods, even healthy ones like carrots and potatoes, were a no-no.
Now, science is learning that the glycemic load was, well, a load of baloney. Research led by scientists at the Jean Mayer USDA Human Nutrition Research Center at Tufts University concluded that the number of calories you eat, not the glycemic load, is what matters most when you’re trying to lose weight.*
The glycemic index, developed by University of Toronto scientists in the 1980s, is a tool that ranks individual foods by the effect they have on blood sugar levels. The higher the index, they theorized, the higher the blood sugar. But many health organizations, including the American Diabetes Association, do not endorse it, arguing that in determining blood sugar levels one’s overall diet is significantly more important than individual foods.
In the USDA’s carefully-controlled randomized trial, Dr. Susan B. Roberts and colleagues followed 34 healthy overweight men and women, average age 35, for a total of one year. Half were on a low-glycemic-load diet; the other half followed a high-glycemic plan. Both diets were designed to cut calories by 30 percent, and both groups were encouraged to limit fat and eat a lot of fiber-rich, healthful foods like fruits and vegetables.
The first six months, the scientists provided the dieters with all their food. The next six months, the dieters followed their eating plans on their own.
Identical weight loss
After one year, the low-glycemic-load dieters ended up losing about 8% of their initial weight – and so did the high-glycemic-dieters.
“These finding provide more detailed evidence to suggest that diets differing substantially in glycemic load induce comparable long-term weight loss,” stated Dr. Roberts and team.
The scientists also found no differences between the two diet groups in calorie intake, hunger, satiety, metabolic rates, and body fat loss.
Identical drops in blood sugar and triglycerides
And interestingly, drops in blood sugar and triglyceride levels, the two areas that a low-glycemic diet has been promoted as being particularly beneficial for, did not differ between the two diets. Blood sugar and triglycerides dropped significantly, and at virtually the same rate, in both the low- and high-glycemic dieters.
Improvements in HDL good cholesterol, total cholesterol, LDL bad cholesterol, and insulin levels were similar for the two groups as well.
Focus on fiber-rich foods, not glycemic load
For losing weight and keeping it off, the scientists concluded that the focus should be on calories rather than glycemic load, and those calories should come from a diet full of healthful, fiber-rich, water-rich, high-satiety foods like fruits, vegetables, whole grains, and beans.
Several leading nutrition scientists agree, including the expert committee appointed by the USDA to develop the U.S. Dietary Guidelines. The committee wrote: “Current evidence suggests that the glycemic index and/or glycemic load are of little utility for providing dietary guidance for Americans.” **
* American Journal of Clinical Nutrition, 2007; 85: 1023.
** Report of the U.S. Dietary Guidelines Advisory Committee on the Dietary Guidelines for Americans, 2005 (www.health.gov/dietaryguidelines/dga2005/report/)