Is This Any Way to Choose Foods?

Glycemic index is a term bandied about a lot these days. The Atkins, South Beach, Zone, and Sugar Busters diets advise against foods high on the glycemic index, and thus against many grain products, fruits, and vegetables. People with diabetes may hear about it. Is it something you really need to bother about?

The index is not an easy concept. To understand it you have to start with carbohydrates, and most people have only a hazy idea what these are and which foods are rich in them. In fact, about half our foods are high in carbs -- orange juice, beans, sugar, milk, pears, strawberries, all types of flour, broccoli, soda pop, apple pie, corn, biscuits, green peas, muffins, honey, sweet potatoes, and so much more.

Simple and not simple

Carbohydrates are the main source of calories in virtually every diet worldwide (the other calorie-providing components of foods are protein and fat). Most come from plant-based foods; dairy products are the only animal-derived foods with lots of carbs. All carbohydrates (except for fiber) are transformed by the body into blood sugar (glucose), the body's basic fuel.

There are two general types of carbohydrates: simple and complex. The simple ones are sugars: glucose and fructose from fruits and some vegetables, lactose from milk, sucrose from cane or beet sugar, and others. Many of the simple carbs are sugars added to processed foods such as sodas and cookies. Complex carbs, which are chains of sugars, consist primarily of starches, the storage form of carbohydrates in plants. Foods rich in complex carbs include grains and grain products (such as bread and pasta), beans, potatoes, corn, and some other vegetables.

This is where the glycemic index comes in. It ranks foods by how fast their carbs are digested into glucose and absorbed, and thus how rapidly and how high they cause blood sugar to rise—which in turn affects insulin levels. The higher the number, the greater the food's effect on blood sugar. You might think that simple carbs such as table sugar would cause blood glucose to shoot up the most, but not necessarily. Instant rice is at the top of the list for fast release of sugar, along with white potatoes, watermelon, raisins, carrots, pretzels, rice cakes, most breakfast cereals and crackers, and white breads. Beans and unrefined grains are generally low on the list.

A guide, but to what?

If you were eating one food at a time, the index might be of some use. In real life, however, we usually eat mixed meals, and many factors come into play that can make hash of the glycemic index. The factors that alter the digestion and absorption of carbs, and thus the blood sugar levels that result, include the amount of fiber, fat, and protein in the food, how refined the ingredients are, whether the food was cooked, and what other foods are eaten at the time. Potatoes are high on the index, but if you eat them with meat or cheese, or make them into chips, they are digested more slowly. If you mash a potato, it moves up even higher. The riper the fruit is, the higher on the index. Adding vinegar to a meal can reduce its glycemic impact. Surprisingly, adding plain old sugar to a meal has no effect on the glycemic index of the meal. Because of all these variables, the glycemic index is of little practical use for designing an eating plan.

Moreover, it's not even clear that avoiding foods high on the index is beneficial. Some research suggests that diets high on the glycemic index are more likely to lead to diabetes, heart disease, and obesity, but the evidence is mixed. Thus, the American Diabetes Association, for instance, does not recommend using the index in the prevention or treatment of diabetes. The notion that foods high on the index make people feel hungrier sooner remains unproven.

But, you may ask, if a food promotes high levels of glucose, which in turn provokes the release of high levels of insulin, which in turn is associated with insulin insensitivity and diabetes, shouldn't a person avoid those foods? Perhaps so. The trouble is, the glycemic index does not accurately predict how much insulin the body will release in response to blood sugar, according to a review of studies by Dr. Xavier Pi-Sunyer, a well-known expert on diabetes at St. Luke's Roosevelt Hospital Center in New York City. Portion size is more important than the specific foods a person eats. It all breaks down into confusion when you learn that lentils (low on the index) provoke higher insulin levels than potatoes (high on the index).

Dr. Pi-Sunyer's conclusion: People (and the experts advising them on nutrition) can find more worthwhile issues to concentrate on than the glycemic index.

Practical lessons

Don't try to build your diet around the glycemic index. The main problems: it deals with single foods eaten by themselves, and its health benefits remain unproven. Yes, it's good to limit your intake of (or avoid) some high-index foods, such as white bread. But there is no reason to avoid all foods high on the index—many are very nutritious, such as carrots. Moderation is the key. If foods high on the glycemic index play any role in diabetes, it may be simply that people eat too much of them and gain weight.

Choose foods rich in fiber and unrefined complex carbohydrates—that is, fruits, vegetables, beans, and whole grains. They are nutritious, filling, and relatively low in calories. Many are also low on the glycemic index. If you're trying to lose weight, calories do count, far more than the glycemic index. In fact, all the current diets built around the index have another thing in common—they get you to cut calories, even as they tell you that calories don't count.

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