It's no secret that white rice, white potatoes, and white sugar are fast becoming the diet "bad" guys. And people who commit to The G.I. Diet (Workman, 2003) learn right away to avoid these and many other foods. The plan is based on a system called the glycemic index (G.I.), a scientific ranking that classifies foods based on how quickly they raise blood sugar. Author and businessman Rick Gallop, past president of the Heart and Stroke Foundation of Ontario, developed the diet to help friends who were struggling to lose weight. His strategy: Avoid foods that cause blood sugar levels to fly sky-high. Gallop says such foods trigger the release of insulin, promoting fat storage and intensifying hunger. A companion book, Living The G.I. Diet (Workman, 2004), contains 135 recipes, plus suggestions on applying the program to everyday life; the newest book in the series is The G.I. Diet Guide to Shopping and Eating Out (Random House Canada, 2005).

Telling dieters to lay off simple sugars and highly processed grains is smart diet advice, as is encouraging people to eat more whole grains, fruits, vegetables, and lean meats. But as critics point out, relying on the glycemic index to promote weight loss isn't necessarily fail-safe. Most meals, after all, are made up not of single foods but a variety, and foods can have different effects depending on the ways they're combined. For instance, mashed potatoes have a high G.I. But if the rest of the dinner includes pan-seared salmon, a big salad, and steamed broccoli-all of which have low G.I.'s-these dishes will make your body absorb those spuds more slowly. Gallop deserves credit, though, for keeping the choices on his red- and green-light lists healthful. Chocolate-covered peanuts may have a low glycemic index, but on the G.I. Diet, candy is a red-light food; ditto for low-glycemic but fatty meats like bacon and sausage.

Basic principles:

Think "red light, green light." Foods are color-coded into a traffic light system based on their glycemic ratings. For example, bagels and watermelon are labeled "red," or high-G.I., since they cause blood sugar to spike rapidly. Whole grains, broccoli, and lean beef get the "green light" since they have low G.I.'s. Apricots, bananas, and low-fat yogurt merit the cautionary "yellow light."

How the diet works:

In the first of two phases, dieters eat only green-light foods to lose weight. Because foods in this category are naturally high in fiber, low in calories, and filling, they automatically aid weight loss. In phase two, you maintain weight loss with green- and yellow-light foods; exercise is also essential at this stage. The diet breaks down to 55 percent carbohydrate, 25 percent protein, and 20 percent fat.

What you can eat:

Low-G.I. foods-in other words, lots of fruits and vegetables, whole grains, and lean meats. As a plus, you don't have to painstakingly measure portions. Instead, you visually divide your plate into three sections, covering about half of it with fruits and veggies, one-quarter with lean meat or fish, and the remaining quarter with whole-grain starches such as brown rice and whole-wheat pasta.

Does the diet take and keep weight off?

It seems to. The Web site features a number of anecdotal reports from successful dieters. However, there's no scientific evidence to prove that folks who eat only low-G.I. foods will lose weight.

Is the diet healthy?

Yes. The green-light list offers a full menu of low-fat, high-nutrient foods, including lean meats, fish, whole grains, fruits, and vegetables. You can't get any better than that. Of course, since the plan doesn't specify portion sizes, it's possible to overeat, even when it comes to these nutritious choices.

What do the experts say?

"I'm not convinced that glycemic index is the be-all and end-all for weight loss," says registered dietitian Leslie Bonci, director of sports-medicine nutrition at the University of Pittsburgh Medical Center. She thinks Gallop's stoplight system takes a "good food, bad food" approach to eating that can be confusing. Dieters need to understand that some high-G.I. foods like potatoes can be healthful, even nutritious, in reasonable amounts. "If your potato is the size of a canoe, then obviously this is a problem," Bonci says. How you prepare it and how much you eat are the deal-breakers, she adds. Roberta Anding, a registered dietitian, a spokeswoman for the American Dietetic Association, and an instructor in the Department of Pediatrics at Baylor College of Medicine, says she doesn't buy "all the science in the book, but the plan it provides isn't a bad one." In fact, Anding likes the fact that Gallop's lists include the best low-G.I. foods. "Some high-fat foods like ice cream, candy bars, and pizza are low-G.I.," she says. "A consumer could say 'OK, I can have that.' This author doesn't allow you to go there."

Who should consider the diet?

People looking for a fairly simple eating plan. The diet revolves around lean meats and low-G.I. foods-a list that's easy to remember since it basically consists of fruits, vegetables, and whole grains.

Bottom line:

While using the glycemic index for weight loss is controversial, the fact that this diet focuses on the best low-G.I. foods is a good start. Avoid overeating and the plan should work.
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