The good-carb diet: What does science say you should eat?

Americans are diet crazy. According to a March 2003 poll, 20 percent of Americans are on a diet. Another 30 percent said they were planning to go on a diet soon.

And what a selection of diets we have to choose from! To name just a few, there are Atkins, Ornish, Cooper, South Beach, Beverly Hills, Eat Smart, and even one called Help, I’m Southern and I Can’t Stop Eating. Many of these programs overlap, and others seem to flatly contradict each other.

What’s a dieter to do? Which plan will not only help you lose weight but also be good for your long-term health?

The Willett Way

Science has come to the rescue. Many nutritional experts are beginning to agree on a diet that is based on sound scientific research. The diet does not yet have a name, but it might well be called the Willett diet, after Walter Willett, chairman of the department of nutrition at the Harvard School of Public Health.

Willett’s diet plan is put forth in his book Eat, Drink, and Be Healthy: The Harvard Medical School Guide to Healthy Eating. It recommends eating abundant fruits, vegetables, and whole grains and optional portions of fish and chicken. Willett says the diet will improve weight control and help prevent diabetes, maintain clear arteries, and promote overall good health for children, teens, and adults.

“Nutrition used to be like religion,” said Willett. “Everyone said, ‘I have the truth, and everyone else is wrong,’ and there wasn’t much data to refute that. Now we’re starting to have a real scientific basis for understanding what you should eat.”

The Evidence Is In

Willett’s recommendations are based on the largest long-term dietary survey ever undertaken: the 121,700-participant Nurses’ Health Study. The study was begun in 1976 by Harvard Medical School professor Frank Speizer.

Willett has assessed the results of the study since 1980, exhaustively analyzing the health and nutrition of all its participants, regularly collecting samples of blood and even toenails. He launched a second study, including 52,000 men, to be sure that both sexes were represented in the research.

Willett used the studies’ findings to create a new food pyramid, which emphasizes eating vegetables in abundance, nuts and legumes (peanuts, peas), fruits, plant oils, and whole-grain foods at most meals.

Willett says that statistics back up the soundness of his Healthy Eating Pyramid. Study participants whose diets most closely resembled the guidelines lowered their risk of major chronic disease by 20 percent for men and 11 percent for women.

Calling All Carbs?

Willett maintains that dietary advice took a wrong turn in the 1980s, when experts started telling Americans to radically cut down on consumption of fats and oils. The U.S. Department of Agriculture’s Food Guide Pyramid, first released in 1992, reflects that view, he says. It calls for six to 11 servings of bread, cereal, rice, and pasta daily, while fats and oils are to be used “sparingly.”

Willett says the pyramid contributed to obesity by encouraging people to think they could maintain their weight by simply cutting out fat and eating as many fat-free products as they wanted. “If you pen up an animal and feed it grain, it will get fat,” said Willett. “People are no different.”

The problem with overeating low-fat products, says Willett, is that so many of them are made mostly from refined carbohydrates. Carbohydrates are organic (carbon-containing) compounds made by green plants. Sugars, starches, and cellulose are carbohydrates. A refined carbohydrate is one that has been so thoroughly processed that most of its nutrients are gone. Table sugar and white flour are refined carbohydrates.

When a person eats refined carbs, the body quickly converts them to the sugar glucose. Glucose signals the pancreas to produce insulin, a substance that conducts the glucose into the body’s cells for use as energy. Too much glucose over the years, however, can result in insulin resistance, a condition in which the cells reject insulin and the sugar remains in the blood. That rejection goads the pancreas to produce even more insulin, which is also rejected. The result: type 2 diabetes and other significant health problems caused by too much sugar in the blood.

Type 2 diabetes used to be a condition of only older adults, but more and more cases of children with type 2 diabetes are being reported–a problem Willett blames squarely on eating too many refined carbohydrates. Research shows that insulin resistance can also contribute to other serious health problems, such as high blood pressure, heart disease, and some kinds of cancer.

“For many people, particularly overweight people with a high degree of insulin resistance, [refined carbs] produce exactly the opposite of what they need,” Willett said.

The Ratings

Willett’s solution: Replace refined carbs with regular carbs and with other foods that have a low glycemic index (GI). The GI is a number that represents how quickly the body converts a certain food into glucose. A GI of 55 or less is considered to be low, 56 to 69 medium, and 70 or more high. The lower the GI, the more slowly the body processes the food into energy.

Foods with low GIs include whole grain (such as wheat bread, rye bread, oatmeal, and brown rice), plant oils, and vegetables (except for potatoes). A diet rich in foods with low GIs helps keep blood glucose levels stable, since those foods gradually release glucose into the bloodstream and spare the pancreas from overwork.

Steady blood glucose also helps keep the appetite in check, making it easier to maintain a healthy weight, says Willett. Low-carb diets, such as the Atkins diet or the South Beach diet, with their emphasis on meat, fish, and cheese, do maintain steady blood glucose, but Willett says his studies show there are significant health advantages to adding plenty of whole grains and vegetables to the diet.

Bye-Bye Fries?

Will you have to give up French fries for whole-wheat bread to maintain a healthy weight and to protect against diabetes, heart disease, and other ailments? Not totally, says Willett. Most people can summon the willpower to substitute whole-wheat flour for white flour, use unsaturated oils instead of butter or lard, and eat less sugar overall.

“My suggestion is not severely restrictive, because it can be achieved mainly by substitution,” said Willett. In any case, “it does not mean you cannot eat any of [the foods you like] but rather that they should be de-emphasized.”

So take heart. Even Willett has a little chocolate now and then. He recommends that everyone also take a multivitamin and mineral tablet every day.

Oh, one other thing–daily exercise is essential in Willett’s diet plan. Remember what he said about feeding a penned-up animal a lot of grain. Exercise doesn’t have to be strenuous. A half hour a day of moderate activity, such as walking, offers “impressive health benefits,” said Willett.

Note: Adapted with permission from Discover magazine


* What are carbohydrates? (carbon-containing compounds made by green plants)

* What are refined carbohydrates? (carbohydrates that have been so thoroughly processed that most of their nutrients have been removed)

* What is the problem with overeating low-fat food products? 80 many of them are made mostly from refined carbohydrates)

* What happens if the body has too much glucose over the years? (It can result in insulin resistance, which, in turn, can lead to diabetes and other significant health problems caused by too much sugar in the blood.)

* What is a glycemic index (GI)? (a measurement of how quickly the body converts certain foods into glucose)

* What types of foods have a low GI number? (Answers may vary but can include the following: whole grains, such as wheat and rye breads, oatmeal, and brown rice; plant oils; and all vegetables except potatoes)

* What benefit is there to eating foods with a low GI number? (They help keep blood glucose levels stable, which can spare the pancreas from overwork and keep the appetite in check.)


1. Brainstorm with students how to replace carbohydrates that have high GI numbers with carbohydrates that have low GI numbers. Have students make charts, graphs, or posters that display foods that have low GI numbers. The same could be done for foods with saturated and unsaturated fats. The goal is to display healthful foods that can be substituted for the carbohydrates that quickly turn into sugar in the body

2. Have students comparison shop to determine which types of foods are more economical: refined carbs or carbs with low GI numbers. Graph foods according to their GI values: high, medium, or low. What is the average price of one serving from each of the columns?