Health Experts: "Jury Still Out" on Theory Behind Many Popular Diets

American Institute for Cancer Research
Monday, 17 November 2003

Urge Public to Look More Closely at Science Behind Weight-Loss Claims

Health experts at the American Institute for Cancer Research (AICR) today outlined several basic questions that are still unanswered by the Glycemic Index, a theoretical ranking of carbohydrate-containing foods that forms the basis of the Atkins Diet, the South Beach Diet, the Zone, Sugar Busters and several other popular weight-loss plans. The experts said that Glycemic Index is an interesting but still theoretical notion that was seized upon by weight-loss gurus before its real-world usefulness could be objectively determined.

The Glycemic Index is a ranking of how specific carbohydrate-containing foods, when eaten alone, affect the blood sugar levels of a small group of test subjects. The Index was conceived as an attempt to help diabetics gauge their dietary intake. However, over 20 years after the Index was developed, the American Diabetes Association remains unsure that the Index is a practical guide for individuals to follow.

Today the AICR experts went further, saying that because of several inherent limitations in the way the Glycemic Index is conceived, it does not fully address the complexity of a person's diet. Because of this, its relation to weight management remains unproven.

Specifically, the experts noted that by using a scale of 0 to 100 to rank different foods, the Glycemic Index makes relatively minor differences in rates of digestion appear much more significant than they actually are.

But the AICR experts aren't just focused on the methodology behind the Glycemic Index in fact, they're more worried about the way these diets have touched off a fundamental shift in the way Americans approach diet and health.

"What concerns us most about diets based on the Glycemic Index" said Melanie Polk, RD, AICR's Director of Nutrition Education, "is the distorted and potentially dangerous take-home message people are getting: If I want to lose weight, I should eat more meat and fat." Polk said that the problem with this notion, which is increasingly regarded by the public as a truism, is that it just isn't true.

Moreover, diets high in meat are probably linked to increased risk of colorectal cancers, and possibly to cancers of the breast, prostate, kidney, pancreas and bladder, according to the AICR/WCRF report, Food, Nutrition and the Prevention of Cancer: A Global Perspective. The report also cautions that diets high in animal fat are possibly linked to cancers of the lung, colon, rectum, breast, endometrium and prostate.

"There is another issue at work here: what the diet books won't tell you is that plans based upon the Glycemic Index also happen to be, at heart, low-calorie diets," said Polk. "And the bottom line for weight loss is, and will always be, about calorie balance."

There, AICR experts discuss their specific concerns about the methodology behind the Index, and describe what the Glycemic Index can and cannot say about diet, weight management and overall health.

In the paper, the AICR experts conclude that, "due to insufficient evidence of clinical efficiency and persistent methodological concerns regarding how Glycemic Index values are determined, AICR cautions the public not to make dietary changes based solely on this interesting but still unproven concept."

Glycemic Index Offers Deceptively Easy Answers to a Complex Question

The AICR experts say that effective and long-term weight management grows out of a healthy change in lifestyle, not a brief commitment to eating only certain foods because of where they rank on a theoretical chart.

"We already know how to lose weight and keep it off," said Polk. "It's not a secret: eat less, exercise more. Instead of eliminating all carbohydrates, choose whole-grain options and beans with the fiber to fill you up and provide energy throughout the day. Add vegetables and fruits while cutting back on animal protein and fat. "

But many Americans are daunted by such a commitment to long-term change, and find the "quick-fix" promises of Glycemic Index diets appealing. Another reason the Glycemic Index has taken hold, despite its questionable applicability to the world outside of the clinic, is that it seems to explain something many Americans already believe: foods high in fat and protein "fill you up" more than pasta, bread and salad.

"The problem with that belief is that it doesn't hold up to scrutiny," said Polk. "While it may be true that pasta and bread made from refined white flour don't offer long-lasting satiety, whole-grain pastas and breads are considerably more filling. They also offer health benefits that refined grains do not."

And despite the tendency of many diets based on the Glycemic Index to shunt vegetables and fruits to the side, these foods contain fiber that promotes fullness without the excess calories found in animal fat, and belong at the center of weight-management efforts. Recent studies at the University of Pennsylvania show that people who added a large, low-calorie green salad at the start of a meal actually lowered the number of total calories they ate during the meal and felt just as full.

"According to these studies, a large helping of a low-calorie salad tricks the body into feeling full, without overloading it with calories."

The AICR experts said that a simple way to ensure a filling, healthy meal without excess calories is to look at the proportion of food on the plate. Aim for meals composed of 2/3 or more vegetables, fruits, whole grains and beans and 1/3 or less animal protein (meat, eggs, cheese) this will provide filling fiber and long-lasting energy at a substantially reduced calorie cost.

For more information, or to contact American Institute for Cancer Research, see their website at: www.aicr.org

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