Hippocrates, the ancient Greek considered to be modern medicine's founding father, said, "Let food be your medicine." Two thousand years later, Robert Starkenburg, MD, with Kaiser Permanente in Raleigh, NC, says much the same thing: "If you went to Bob's Gas-O-Rama and bought junky gas because it's close to your house and convenient, you would not be surprised when your car didn't run well. But we constantly put bad fuel in our bodies because it's convenient and inexpensive and easier than preparing a variety of fresh foods. And we're surprised that we don't feel good, we don't have energy, we gain weight, we have health problems. But we shouldn't be surprised. We really need to think of food as medicine."

Why Is the Treasure at the Base of the Pyramid?

Most Americans probably have heard that there is a bonanza of health benefits to be had by eating more of the foods found at the bottom of the Food Guide Pyramid. The U.S. Department of Agriculture went so far as to replace the old "food groups" charts we remember hanging on the walls of grade school with the pyramid, recommending that the base of a healthy diet be numerous daily servings of grains, fruits, and vegetables.

But why? Research is under way to identify certain substances in these foods that can help us fight disease and stay healthy. But the field is new, and more studies need to be done. The best advice for a consumer looking for dietary health benefits is to forget about micromanaging and look at the big picture.

"The main thing is to eat a large variety of foods, including plenty of fruits and vegetables," says Sally Willoughby, a registered dietitian with Kaiser Permanente in Atlanta. (But, if you have any health complications, such as diabetes, it is always a good idea to talk to a dietitian.)

Put the Advice in Perspective

The recent burst of food-as-medicine information needs to be put in perspective. Every week, it seems, a new report comes out claiming that a particular food can ward off a certain disease.

Last year, for example, when a Harvard study came out showing that men who consumed at least 10 servings of tomato-based foods each week halved their risk of prostate cancer, every pizza parlor in New York City had newspaper articles about the study taped to the counter. Studies showing that oat bran lowers cholesterol led to the sudden appearance of oat bran muffins in donut shops and various bakeries.

Studies in rats and mice show that eating soy-based foods may lower the risk of breast cancer. A 1994 report showed that people who ate lots of dark, leafy greens, which are rich in chemicals called carotenoids, had a lower risk of developing an eye condition that accounts for nearly 500,000 cases of blindness in America each year.

Although the importance of vitamins (C against scurvy, for example) has been well known for many years, researchers have just begun to catalog other chemicals in food that may have important health effects.

These substances, such as the carotenoids in greens, or the so-called isoflavones in soy, are collectively called phytochemicals, meaning "plant chemicals." The exact effects each of them has, or that they may have in combination, are largely still unknown. Many phytochemicals themselves may still be unknown. Under these circumstances, making recommendations to eat individual foods is difficult.

The great difficulty in doing research on food-as-medicine is us.

"It is almost impossible to control everything a person eats in comparison to controlling the diet of a mouse in a cage," notes Shelly McMahon, a registered dietitian with Kaiser Permanente in Ohio. Researchers get around that problem by trying to figure out what kinds of "natural experiments" have already been done that may supply clues to diet and health. The fact that Asian populations eat a great deal of soy foods and have lower rates of breast cancer is not proof positive that soy is protective, but it is compelling circumstantial evidence. Combine that kind of study with tests showing that mice on a soy-rich diet ward off cancer, and the connection seems like a good bet.

Variety Is the Stuff of Life

Since science is not yet sure exactly what good substance is in which good food, you cannot go wrong by eating them all. A diet rich in fruits and vegetables (make that five servings a day), in addition to grains, will automatically be high in fiber, high in nutrients, and low in fat. It certainly will "do no harm," another favorite saying of Hippocrates, and the phytochemical bonanza in such a diet is a bonus. And if you're going to have that occasional ice cream cone anyway, enjoy it! As the ancient Greeks also used to say, "Everything in moderation, including moderation itself."