Fad diets have touted using the glycemic index (GI)-a measure of how quickly a food boosts blood sugar-as a magic bullet for targeting weight loss. But science keeps finding that the facts are more complicated.
Now researchers in the Netherlands report that the glycemic index may not affect appetite as previously thought. Harry Peters, PhD, of Unilever Research and Development, and colleagues tested the theory that low-glycemic index carbohydrates that digest more slowly and have more gradual effects on insulin and glucose levels might combat hunger better than high-GI foods. So whole grains, for example, might be better for weight loss than white bread or sugary foods-not only because of calories but because they curb appetite more. Results from previous studies of this glycemic response and appetite have been inconsistent, however.
In tests with 35 volunteers, Peters and colleagues compared post-meal appetite and fullness with carbohydrates differing only in their glycemic index. They found only minimal effects on combating hunger with slower-to-digest, low-glycemic carbs.
Peters and colleagues concluded, These results cast further doubt on the notion that slowly digested carbohydrates may influence appetite through their effects on glycemic responses.
Susan B. Roberts, PhD, director of Tufts HNRCA Energy Metabolism Laboratory and author of The I Diet, and colleagues first challenged claims that glycemic index is a panacea for long-term weight loss in a 2007 study. Roberts and colleagues found that study participants achieved and maintained comparable weight loss after one year, regardless of whether they were on a low- or high-glycemic index diet.
But their ensuing research revealed that the whole picture is, again, more complicated. Watching your glycemic index actually does work for about 50% of people, Roberts explains. We were the first to show this and Harvard subsequently found the same thing. When you just look at the whole population it doesnt look great, but for some people it is an effective tool.
Given the latest evidence on glycemic index and diet and Tufts complicated findings, what should someone looking to lose weight do? Roberts advises that while science is working out simple tests that people can use to determine whether a low GI is good for them, being self-aware about hunger can be a great help: Try different breakfasts-for example, high-GI white toast versus low-GI fruit, eggs and a small piece of whole-wheat toast. If you get hungry more quickly after eating the high-GI breakfast, chances are you will do better if you go the low-GI route.
TO LEARN MORE: European Journal of Clinical Nutrition, January 2011; abstract at dx.doi.org/10.1038/ejcn.2010.189.