Glycemic Index Versus Calorie Control

Karen Collins, MS, RD, CDN
American Institute for Cancer Research

A recent study punches a small hole in the popular theory that says a low glycemic index (GI) diet can influence our body’s hormones and make weight loss easier. According to this theory publicized by some researchers and diet books, we can avoid surges in our blood sugar, keep our insulin levels lower and put our bodies in a fat-burning mode, rather than a fat-storing mode, by eating foods with a low-GI value. Some research even suggests that controlling insulin levels with low-GI foods could help reduce the risk of certain cancers. But this new study shows that regulating your calorie intake could affect your weight more than a low glycemic diet.

In this new randomized controlled study, people ate either a high- or low-GI diet for 12 weeks. Both groups lost an equal amount of weight during that time. The reason appears to be the calorie restrictions placed on the individuals based on their energy needs, not the GI value of the foods they ate. The weight loss and/or calorie restriction also appear to explain the equal improvements both groups experienced in their insulin function.

Although more research will be needed to confirm the findings of this study, it presents the first evidence to date refuting the popular idea that low-GI foods lead to metabolic activity that promotes weight loss. In this theory, carbohydrates with a high GI, like sweets, potatoes, white rice and refined grains, are digested quickly, raising blood sugar and leading to a swift insulin response. As a result, it’s been suggested that high GI foods send blood sugars out of control, make weight control more difficult and increase cancer risk. Some studies suggest that high insulin levels might promote the development of colon, breast, prostate and other cancers. Foods with a low GI, on the other hand, are digested and absorbed more slowly, causing a lower rise in insulin. These foods include whole-grain products, beans, and most vegetables and fruits.

‘Glycemic load’ is the term in this theory used for the combined GI value of the foods someone eats and the amounts eaten. Several studies suggest that a diet with a high glycemic load doubles the risk of heart disease in those who are overweight. One recent study showed that people on a diet with a low glycemic load lost more weight, especially more waistline fat, than another group on a high glycemic load diet. Advocates for this theory say that a low glycemic load diet may promote weight loss by keeping people’s hunger satisfied longer or by mobilizing the body to burn body fat. But some studies on low glycemic load show no weight difference, so a person’s calorie intake could be the critical factor for any weight loss this diet might bring.

Calories could also explain any glycemic connection to cancer risk. A variety of studies suggests that keeping insulin levels from rising could directly protect against cancer. Yet research paints a mixed picture about any link between glycemic index or glycemic load and cancer risk. Some studies link high GI foods or high glycemic load to a range of 24 to almost 72 percent greater risk of colon, pancreatic, prostate, uterine, stomach, or postmenopausal breast cancers. But some studies show that only the overweight are at risk, while other studies show no link at all.

Even if glycemic load does affect weight control or cancer risk, it’s more than likely that calorie control has as much or greater influence. To incorporate both ideas in your eating habits, take appropriate portion sizes of mostly plant-based meals and snacks that include a wide variety of fruits, vegetables, whole grains and beans. This type of diet should have a fairly low glycemic load. This type of diet with its many nutrients and phytochemicals also offers the most proven protection against cancer, when combined with regular exercise for optimal weight control.


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