Glycemic Index: New Way to Count Carbs?

Evidence Mounts for Low-Glycemic Index Diet to Control Diabetes

Author: Sid  Kirchheimer
 
Aug. 20, 2003 — A carb is not a carb is not a carb — at least when it comes to diabetes and getting control of high blood sugar. A low-glycemic index diet may be the way to go, say researchers.

Even foods with the same carbohydrate content can trigger a wide difference in blood sugar levels — as much as fivefold. It all depends, say some researchers, on the food’s glycemic index, a number that indicates how much and how quickly blood sugar increases after consuming a carbohydrate-containing food.

Why Glycemic Index Matters

Foods with a high glycemic index (and therefore a higher number) cause a sudden and drastic jump in blood sugar levels. Low-glycemic foods are more easily absorbed in the body and raise blood sugar more gradually.

In the latest research, Australian researchers analyzed data from 14 previous studies comparing the effects of high- and low-glycemic foods on blood sugar levels in people with diabetes. They then looked at results of a blood test called HbA1c, which indicates average blood sugar levels over the past three months.

Good Enough for a New Drug

Researcher Jennie Brand-Miller, PhD, and colleagues found that patients who ate a low-glycemic index diet reduced their HbA1c levels by an average of 0.43 points above that produced by the high-glycemic index diet.

“That’s significant — enough of a reduction to get a new [diabetes] drug to market,” says Gerald Bernstein, MD, former president of the American Diabetes Association and an endocrinologist at Albert Einstein College of Medicine.

“There is no question that it’s important for diabetics to pay close attention to the glycemic index of foods they eat,” says Bernstein, who was not involved in the study conducted by University of Sydney researchers.

“Remember, the issue in diabetes is an inability to handle glucose. Whether or not you’re taking insulin, you’re trying to match the body’s insulin with the onslaught of glucose going in. So you really need to know the probability of how quickly blood sugar is going to bounce so you can better manage your disease. When you eat a baked potato, glucose levels spike in milliseconds. With legumes or fruits and vegetables, they go up in about 30 minutes.”

What’s High, What’s Low?

Although important, the numbers can also be confusing because the glycemic index of some foods may surprise you. As a general rule, the same low-fat, high-fiber fare — fruits, vegetables, and whole grains and legumes — often advised to manage weight and help prevent diabetes and other health conditions, have a low glycemic index. Conversely, starchy and processed foods such as potatoes, breads, and cereals usually have a high glycemic index.

But there are exceptions. For instance, a bowl of All-Bran cereal has a glycemic index of 54, while a serving of spaghetti rates at 41, meaning the high-fiber cereal spikes blood glucose more quickly and drastically. A handful of raisins is 64, more than a serving of popcorn, at 55. White rice (56) has nearly twice the glycemic index of a glass of apple juice, and an orange (43) has almost half the index of watermelon (72).

The American Journal of Clinical Nutrition lists any food under 55 as a low-glycemic food and any food more than 70 as high glycemic.

Haagen-Dazs vs. Baked Potato

“I remember one study that compared various foods found that a bowl of Haagen-Dazs ice cream raises blood glucose at a slower rate than a baked potato,” Bernstein comments.

Still, the use of diets with low glycemic index in the treatment of diabetes remains controversial. There are contrasting recommendations around the world, the Australian researchers note in their study. It appears in this month’s issue of Diabetes Care.

One possible reason: Most of the studies thus far measuring blood sugar response to glycemic indexed foods have been encouraging but small, says Angela D. Liese, PhD, MPH. Liese recently completed her own research on how foods with high glycemic indexes affect “metabolic syndrome” — a cluster of conditions that includes obesity, high blood cholesterol, high blood pressure, insulin resistance, and diabetes. Her results have not yet been published.

The australian researchers’ analysis of 14 studies had a total of only 356 patients.

Time for a Change?

“This study is important because it shows some really encouraging data, but a lot more research is needed,” says Liese, an epidemiologist at the University of South Carolina. “If you want to get to the point of reaching new dietary recommendations, much, much larger studies are needed.”