Health experts at the American Institute for Cancer Research (AICR) released in November 2003 a list of 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 (GI) is an interesting but still theoretical notion that was seized upon by weight-loss gurus before its real-world usefulness could be objectively determined.

AICR cautions the public not to make dietary changes based solely on this interesting but still unproven concept.

What Is the Glycemic Index?

The Glycemic Index ranks carbohydrate-containing foods by how quickly they elevate blood sugar levels.  It is measured by comparing the increase in blood sugar after eating 50 grams of carbohydrate from a single food to the increase in blood sugar that occurs after eating 50 grams of carbohydrate from a reference food, either glucose or white bread.

Proponents of the Glycemic Index argue that foods that raise blood sugar quickly – foods that have a “high GI” ranking – stimulate hunger, increase enzymes that promote the storage of fat and reduce the body’s ability to burn fat.

Why Is It Controversial?

Critics of the Glycemic Index maintain that it is only a reference tool, and as such has several limitations that cannot account for the kind of complexities that occur outside of a laboratory environment.

Criticisms of the Glycemic Index

• The GI of a food is not a fixed, unchanging figure – it varies considerably from person to person.  It even varies within the same person, depending upon a host of complicating factors.
• The scale used by the GI to measure differences in rate of digestion makes those differences seem larger and more significant than they actually are.
• The GI of a food is based upon an arbitrary amount of carbohydrate (50 grams) that may or may not correspond to the amount of food that is typically eaten.  Attempts to correct for this built-in abstraction (by calculating the glycemic load) only serve to magnify the abstraction even further.
• People don’t eat individual foods – they eat meals.  Studies investigating the applicability of the glycemic index for meals remain contradictory.
• There is still disagreement about how to calculate the Glycemic Index in the first place.  Basic questions about the method of calculation, timing of blood sugar testing, and whether to use glucose or white bread as a reference food – along with a host of other factors – still need to be resolved

Concerns About Diets Based on the Glycemic Index

“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. We already know how to lose weight and keep it off.  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 American are daunted by such a commitment to long-term change, and find the “quick-fix” promises of Glycemic Index diets appealing according to the AICR.

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

Source:  American Institute for Cancer Research, www.aicr.org.