As diets go, an approach that aims to minimize blood sugar spikes - promoted in such popular books as "The Zone" and "Sugar Busters!" - seems to defy nutritional common sense.

The approach, known as the low-glycemic-index diet, places carrots near the top of the do-not-eat list. Right behind carrots are other foods usually thought of as healthful: potatoes and brown rice. Legumes, fruits and low-fat dairy products still get the nod.

But in the diet, M&M candies are held to be the equivalent of low- fat yogurt with fruit. And Snickers bars rate more favorably than Cheerios or cornflakes.

"It's not intuitive at all," said Susan Raatz, a research bionutritionist at the University of Minnesota's general clinical research center.

The unconventional, low-glycemic-index diet is based on choosing foods that minimize spikes in blood sugar levels. It is a hot topic in the world of nutrition. The word in its name, glycemic, refers to blood sugar.

Widely adopted in Europe, Canada and Australia, the approach remains controversial in the United States, where it's been the focus of several diet books and at least two cautionary position papers from major medical organizations.

In March, the American Diabetes Association said the glycemic index has limited value in diabetes prevention or in choosing a healthy diet.

"There is a lot of misunderstanding about glycemic index and it is easy to misuse the concept," said dietitian Ann Coulston in a statement from the Diabetes Association. "For example, some people use it inappropriately to malign wholesome foods such as potatoes and rice. In fact, there are no data showing any adverse effect from eating these starches."

The eating approach, which assigns food a numerical value, or index, based on how much it raises blood sugar, made it onto the agenda at the Minnesota Medical Association's annual meeting last fall. A physician asked the organization to endorse study of the approach's value and recommend the plan to patients across the state. The measure was not approved.

Sugar-surge theory

At the heart of the low-glycemic debate is whether the approach promotes speedy weight loss and wards off adult-onset diabetes and heart disease, as advocates claim.

The theory underlying these claims is that starchy foods are quickly digested, causing blood sugar levels and then insulin levels to rise rapidly after a meal.

Insulin is a hormone made by the pancreas. The body releases it after eating to escort sugar into cells for energy. The process returns blood sugar levels to normal.

Advocates - such as Australian nutrition expert Janette Brand- Miller - claim that minimizing blood-sugar spikes and the subsequent insulin surge promotes weight loss by reducing feelings of hunger. Insulin surges can reduce the body's blood sugar too much, triggering another urge to eat to correct those feelings.

Excess insulin surges are also thought to wear out the pancreatic cells that make this hormone, setting the stage for adult-onset diabetes, which occurs when the body doesn't make enough of the hormone or resists its effects.

In addition, high blood sugar may raise blood pressure and increase the risk of blood clots.

So why aren't U.S. nutrition experts or medical organizations embracing the low-glycemic-index diet?

One of the main reasons is apparent to anyone looking at a glycemic index food list, where Mars bars and Haagen-Dazs ice cream appear healthier choices than whole-grain breads or cereals.

The amount of fat or protein that a food contains slows the digestion process, said Susan Moores, a Minneapolis dietitian and spokeswoman for the American Dietetics Association. Fatty foods - which are linked with obesity, heart disease and other health problems - can appear artificially healthful based on their glycemic index.

That's why Snickers and ice cream stack up well on this diet's food list against starchy vegetables such as carrots and corn.

"You can't just look at one thing," Moores said.

A healthy diet

The glycemic index also ignores other nutrition facts, she added. A healthy diet is composed of a variety of foods - from whole grains to fresh fruits and vegetables.

Eliminating certain foods from the diet - such as potatoes or carrots - based only on their glycemic index number, may leave key nutrients out of the diet, Moores said.

Carrots, for example, are rich in beta carotene and antioxidants also thought to fight disease, she noted.

They're also low in calories - something that some foods with a low-glycemic index are not, said Raatz.

Focusing only on a food's glycemic-index number ignores the need to control calories and portion sizes, Raatz said. Along with exercise, these remain the critical components of any weight-loss program - no matter where the foods eaten register on the glycemic index.

"You can't ignore these," she said.

More research is needed to establish the value of the low- glycemic-index diet, said Dr. Donald Hensrud of the Mayo Clinic in Rochester, Minn. While some studies have suggested a benefit, he said, there are concerns about methodology.

Many other studies have found the low-glycemic-index diet to be of little value in disease prevention. The American Diabetes Association said studies suggest that this diet offers few benefits, yet has no adverse effects. "Glycemic response has been shown to depend on many factors,"said Anne Daly, president of the health care and education committee for the diabetes association. "The total dietary pattern and the total amount of carbohydrate is more important the individual glycemic index of any single food."

Dr. Richard Bergenstal, head of Park Nicollet's International Diabetes Center in St. Louis Park, has encountered a more practical problem with the glycemic index, which he and his staff sometimes recommend as one tool to make better food choices.

Most food labels don't contain glycemic index numbers, said Bergenstal and Jill Flader, assistant manager of adult diabetes education. Many foods, especially processed ones, have not been given a glycemic index number.

"We don't have any qualms that the glycemic index makes some sense, but just going to that as your guide for healthy living and nutrition misses the bigger picture," Bergenstal said.

WEIGHING IN

Low-glycemic-index diet

The theory: People on the low-glycemic-index diet watch for foods that can cause blood sugar levels to spike. Advocates say that avoiding these spikes promotes weight loss because the body's attempt to correct high blood sugar levels can bring on hunger. They say that blood sugar spikes also may be linked with adult-onset diabetes and heart disease.

Experts' reaction: While some studies have linked the diet to better health, many nutrition experts say more research is needed. Experts caution that a food's effect on blood sugar is only one factor in nutrition. Calories, fat, carbohydrates, fiber, vitamins and minerals must be considered. In addition, the glycemic index - a measure of a food's effect on blood sugar - is not available for all foods.

Foods and blood sugar

The glycemic index measures a food's effect on blood sugar. Anything under 70 generally means the food does not raise blood sugar much. The low-glycemic-index diet is promoted as a way to lose weight and ward off diabetes and heart disease.

Foods Glycemic index number

• Potatoes 80-100
• Cheerios cereal 83
• Whole grain bread 72
• White bread 70
• Rye bread 65
• Mars candy bar 65
• Ice cream, full-fat 61
• Banana 53
• Pineapple 52
• Baked beans (canned) 48
• Chocolate bar 45
• Orange 43
• Pumpernickel bread 41
• Apple 36
• Low-fat yogurt 33
• Skim milk 32
• Lentils 28
• Whole milk 27
• Soybeans 18

Source: Diabetes News: Nutrition Today.

January 2003 News Article Index