The Good Carbs

Despite controversy, the glycemic index system for rating carbs may be a way to help you beat diabetes, heart attacks, an appetite that's out of control, and more..and it's on its way.

Sounds complicated, but it isn't, thank heaven. What it is, some health experts believe, is the most exciting nutrition breakthrough on the horizon.

Invented in the early 1980s by University of Toronto researchers as a tool to help control diabetes, the glycemic index ranks carbohydrate foods by their effect on your blood sugar levels. Today, it's an accepted diet strategy for helping control diabetes in Canada, Australia, England, and elsewhere. And for that reason alone, it deserves more attention here.

But the biggest surprise of all seems to be that the glycemic index may offer dramatic health benefits not just for diabetics but for almost everyone.

"We're learning that the type of carbs you eat really makes a difference in your health," says glycemic index researcher Christine L. Pelkman, PhD, of Pennsylvania State University in State College. And the glycemic index helps you choose the best carbs for you.

With our easy guide to 125 foods, you can use the glycemic index to choose meals and snacks that give you an edge against diabetes, heart attacks, and possibly even cancer. And don't be surprised if you find yourself losing weight to boot.

Good Carbs, Not-So-Good Carbs
The glycemic index (or GI for short) assigns carbohydrate-containing foods a number based on how they affect your blood sugar, or blood glucose, after you eat them. Foods with a GI less than 55 cause only a little blip in blood sugar; those in the 55 to 70 range raise it a little higher; and carbs with GIs more than 70 send blood sugar soaring. We're learning that low-GI carbs are healthy; high-GI carbs, in excess, are not.

What explains the difference in numbers? No matter what form the carb initially takes--the lactose in milk, the starch in a bagel, the sucrose in table sugar--eventually, your body breaks it down to glucose. Glucose winds up in your bloodstream, fueling your cells. What makes a GI number high or low is how quickly the food breaks down during digestion. The longer your body has to wrestle with the carb to break it down into glucose, the slower the rise in blood glucose and the lower the GI.

But it's not always easy to predict a food's GI. Often, fiber-rich foods have lower GIs. Fiber, especially the soluble type in oats and beans, creates a web in the intestines that traps carb particles. Not surprisingly, beans have low GI numbers.

But when fiber is ground finely as it often is in whole wheat flour, it doesn't present enough of a digestive challenge to lower the GI of these foods. That explains why whole wheat bread has a GI number nearly identical to white bread. (But whole wheat bread is still a healthier choice than white bread because of its extra fiber and other nutrients.)

Surprisingly, table sugar has a lower GI than potatoes. That's because it's made of two sugars, glucose and fructose; the glucose half sails right into the bloodstream, but the fructose segment has to detour through the liver, where it slowly gets converted into glucose. But the starch molecules in potatoes are strings of glucose. Boiling, baking, or mashing a potato causes the starch molecules to burst, making it so easy for glucose to enter the bloodstream.

High GI = High Risk
The problem with eating lots of high-GI foods is this: When your blood sugar soars, so does the hormone insulin. Insulin's main duty is to scoop up excess blood sugar and store it safely in muscle tissue. In moderation, insulin is a good guy, but it becomes a killer when its levels spike repeatedly, triggering diabetes, heart disease, and possibly cancer.

Unfortunately, insulin is spiking all the time in the millions of Americans who dote on high-GI fare such as bagels, doughnuts, french fries, and other quickly absorbed starchy carbohydrates. Experts point out that modern diets offer vastly more opportunity to eat starchy high-GI foods than the diets on which human beings evolved.

Taming the Killers
The good news is, switching to a low-GI diet results in a minimum outpouring of insulin, and that has healthy ramifications all over your body. Here's what a low-GI diet appears to help you do:

Stop diabetes.
Diabetes, which is characterized by higher than normal blood sugar, has reached epidemic proportions in the US, afflicting 16 million Americans. Most have type 2, prompted by two very American conditions: excess weight and a sedentary lifestyle. And millions more are walking around with a degree of insulin resistance just shy of diabetes.

"The beauty of the glycemic index for diabetics is that it not only helps control blood sugar and insulin, but its appetite-suppressing effects help them lose weight. And weight loss alone can reverse type 2 diabetes," declares Marc Rendell, MD, director of the Creighton Diabetes Center at Creighton University in Omaha, NE, and medical director of the Rose Salter Medical Research Foundation in Baltimore. Although he believes it's entirely possible to induce remission of many cases of type 2 diabetes using the glycemic index, he urges patients with diabetes to continue their current therapies and only add low-GI foods in consultation with a physician or registered dietitian.

So far, research testing low-versus high-GI diets for diabetics is promising. A 1999 Swedish study of type 2 diabetics found that 4 weeks on a low-GI diet lowered blood glucose and insulin by 30 percent compared to a high-GI diet. In a recent 4-month study led by the University of Toronto's Thomas Wolever, MD, a low-GI diet markedly improved insulin sensitivity in a group of prediabetic insulin-resistant people. "If these trends were sustained--and I'm trying to get money to extend the study--these people could probably avoid getting diabetes," predicts Dr. Wolever.

Which is exactly the implication of several large-scale diet surveys. In a 6-year study of male health professionals, men eating the lowest-GI diets were 25 percent less likely to get diabetes. In the Nurses' Health Study, the most powerful diabetes protection--a drop in risk of one-third or more--came from eating a low-GI diet and getting lots of fiber from cereal (7.5 g daily).

Drop pounds.
Ever feel hungry just an hour or two after a meal? It could be because the meal had a high GI. Ironically, high-GI meals cause such a flood of insulin to cope with all the glucose that blood sugar levels wind up lower than if you'd never eaten. And low blood sugar may send out hunger alarms, according to Susan Roberts, PhD, professor of nutrition at Tufts University in Boston and author of Feeding Your Child for Lifelong Health (Bantam, 1999). In one study, overweight children (average age 10) at Children's Hospital in Boston spent 4 months on either a low-GI diet or a low-fat diet of equal calories. The clear winner: the low-GI diet, with an average weight loss of 4.5 lb compared to 2.8 lb on the low-fat diet.

Dr. Roberts suspects that high-GI carbs are partly behind America's epidemic levels of obesity. "GI is not the complete answer to everyone's weight problem," she says. "But aside from the research, I am personally convinced that low-GI diets help people lose weight, myself included. My husband and I were eating a relatively high-GI instant oatmeal or low-GI Irish oatmeal for breakfast, and I'd call and ask how he felt 2 hours later. Both of us noticed a big decrease in hunger with the low-GI oatmeal. Now I've become very aware of the GI of what I eat and quite consistently find myself hungrier after very high GI foods such as bagels, mashed potatoes, and the like."

Keep your heart strong.
High levels of insulin wreak havoc on the heart. "Elevated insulin triggers a bevy of heart disease risk factors," says Michael Zemel, PhD, chairman of the department of nutrition at the University of Tennessee in Knoxville. Dr. Zemel reviewed the connections between the glycemic index and heart disease for a scientific journal and found that they include high blood pressure, increased fat storage, high triglycerides (a type of blood fat), and lower levels of HDL (the good cholesterol carrier).

Once again, low-GI foods appear to be the Rx. In the Nurses' Health Study, women eating diets with the most carbohydrates from high-GI foods were nearly twice as likely to develop heart disease.

Thwart cancer.
A high-glycemic index diet may even be linked to colon cancer. The hypothesis: The flood of insulin, glucose, and blood fats that stem from a high-GI diet fuels colon cancer cells. Both human and animal research support this theory. For instance, colon cancer patients are prone to insulin resistance, and giving insulin speeds up the development of colon cancer in rats.

Stay energetic and alert.
Want more stamina? You have greater endurance when you exercise after a low-GI meal compared to a high-GI meal, most studies show. And low-GI meals might also give you a mental edge, hints Australian research. People who ate a low-GI breakfast (based on All-Bran) scored higher in a test of alertness than those who ate a high-GI breakfast (based on cornflakes).

"I think the low-GI breakfast increased alertness for two reasons: by fueling the brain with a slow, steady supply of glucose and by staving off hunger. People eating this breakfast didn't get hungry before lunch, while those eating cornflakes did. It's easier to be alert and focused when you're not hungry," speculates study leader Susanna Holt, PhD, RD, of Sydney University's Human Nutrition Unit.

While organizations in other countries, such as the Canadian Diabetes Association, Australia's International Diabetes Institute, and the World Health Organization, all recommend including low-GI foods as part of managing diabetes, the glycemic index gets only a brief mention in the most recent practice guidelines from the American Diabetes Association (ADA).

"At this point, we don't recommend the glycemic index because not enough is known, and there's no evidence that this method is better than the standard approach of counting carbohydrates," explains Marian Parrot, MD, vice president of clinical affairs for the ADA. Although Dr. Parrot agrees that the GI is "not harmful" and that "nothing is wrong with the science," her main objection is that it's too complicated--people just can't be expected to remember and deal with all those numbers. And in fact, a substantial group of health experts agree that although the glycemic index may prove useful someday, it is "not ready for prime time."

But in response, Creighton Diabetes Center's Dr. Rendell, who wrote a recent editorial backing the glycemic index in the prestigious New England Journal of Medicine, believes there's a bias against publishing research in this area. "It's just not politically correct. I've seen excellent research papers on the GI get put aside by medical journals; unfortunately, the best studies haven't been published," he asserts.

"The authorities in the field are too hung up on arithmetic," he says. "For instance, they bring up the fact that carrots have a high GI, so they're afraid people will stop eating carrots." But GI experts never advise avoiding high-GI foods that are low-calorie salad vegetables or fruits. "If high-GI foods such as carrots are also low in calories, you'd have to eat pounds of them to make much of an impact on blood sugar," says the University of Toronto's Dr. Wolever, coauthor of The Glucose Revolution (Marlowe & Co., 1999).

He recommends targeting those high-GI foods that are also high in calories, such as baked goods, highly refined breakfast cereals, and potatoes. Start to replace them with lower-GI foods, such as trading in bagels for 100 percent stone-ground whole wheat bread, instant rice for barley, or cornflakes for All-Bran. "Switching to these low-GI starches," says Dr. Wolever, "can make a tremendous difference in your health."