Experts Study Why Carrots a Day, and Other Veggies, Keep Us Healthy : Medicine: Throughout the world, scientists research fruit, vegetable and grain components that may combat cancer, heart disease.

NEW YORK —  Federal agricultural researcher Jim Duke is taking no chances: Once a heavy smoker, he now eats two carrots every morning on the way to work.

“Can I really help prevent cancer by eating carrots? I’m not positive I’m doing myself some good, but I’m relatively certain I’m not doing myself any harm,” Duke says.

Health authorities have for years been nagging Americans to pile fruits, vegetables and grains on their plates, and it’s been clear from epidemiological studies that people with plant-based diets generally are healthier.

But it’s not been clear exactly why.

“All plants contain components that will prevent cancer, all plants contain components that will cause cancer. All plants contain, I think, components that will lower the blood pressure,” said Duke, who has compiled a huge database on food’s preventive powers.

“But until you know how much is in the plant and how much it takes to do the trick you’re not saying much.”

In laboratories around the globe, scientists are at work figuring that out. Much of the research is aimed at our worst chronic diseases, cancer and heart disease. Some plant components seem to act as antioxidants, which make cells less susceptible to cancer, and some as protease inhibitors, which work against the uncontrolled cell division characteristic of cancer.

Other components appear to keep blood platelets from sticking to walls, helping prevent heart disease.

“There are a huge number of compounds that really very little attention has been paid to. A lot have little nutritional value but do have some impact, and in animal experiments turn out to be protective,” said Lee Wattenberg, a researcher at the University of Minnesota in Minneapolis and a pioneer in research into cruciferous vegetables.

Among the “hot” foods these days are those that contain beta carotene (orange and dark, leafy green vegetables) and those known as cruciferous (broccoli, kale, cabbage and others). Both groups are thought to have some power to prevent cancer.

Garlic and onions, long favorites of researchers, may have some ability to lower blood cholesterol, and high-fiber beans may protect against colon cancer. Eating olive oil and oily fish in place of other fats could also help protect against heart disease.

Chile peppers, ginger, yogurt and a host of other foods are being prepared in labs as well as in kitchens these days.

Occasionally, research runs counter to puritanical notions of what’s healthy. The idea that moderate amounts of alcohol, perhaps red wine in particular, could help protect against heart attacks has upset people who say drunk driving and alcoholism make it dangerous to recommend any drinking at all.

Despite all the research, there are not yet many explanations of the mechanisms at work in what writer Jean Carper calls the “food pharmacy.”

“At the moment, it certainly appears to be that there are certain foods that are so good for you, fish being one, that people should be eating fish because they do not know for sure that it’s only the oil,” said Carper, who has chronicled the research in “The Food Pharmacy” and “The Food Pharmacy Guide to Good Eating.”

So what do you do if you have a family history of heart disease or breast cancer or some other disease?

Certainly a few carrots and a stalk of broccoli each day won’t cancel the effects of smoking or a high-fat diet. And doctors are not likely to make specific diet prescriptions.

At least for now, the advice holds: Eat a low-fat diet that includes a lot of different plant foods.

Part of the problem is that it may turn out to be a combination of foods that pack the disease-fighting power.

Also, it’s difficult to reach a consensus and issue a public policy about, say, adding two carrots a day to the diet. Before the government or other authorities would give such advice, science would have to prove both that it worked and that no population would be harmed by following it, said Catherine Woteki, director of the Food and Nutrition Board at the National Academy of Sciences.

“People are always looking for a magic bullet and prescription that eating a carrot a day is going to improve your health or reduce your risk of cancer,” said Carolyn Clifford, chief of the Diet and Cancer Branch of the National Cancer Institute. “The general population could take that, and if they only ate carrots, they would not have a balanced diet.”

“I try to follow dietary recommendations because I really believe diet has an impact on health,” said Marion Nestle, who chairs the nutrition and food management department at New York University and who edited the 1988 Surgeon General’s Report on Nutrition and Health.

But picking foods to fight diseases? An overall good diet is the answer, she said.

For a century or so, medicine has focused on pharmaceuticals to cope with illness. Ironically, as our sedentary, high-fat modern lifestyles have contributed to the incidence of chronic diseases, research is turning to food, which for centuries was considered to have powers to prevent or cure diseases.

“Why is all this seemingly suddenly catching on?” Carper asks.

U.S. doctors, she says, are trained to use drugs and to cure, rather than prevent, disease. In other parts of the world, particularly China and Japan, natural substances have long been used as medicine.

But scientists now are applying modern techniques to food compounds.

The National Cancer Institute has funded a $20-million Designer Foods Program for five years to try to isolate and standardize useful substances in foods.

The first round of studies involve aged garlic extract, licorice extract, citrus juice, a mixed-vegetable beverage and soybean meal. So far, some pure food compounds fed to animals have inhibited carcinogens, NCI’s Clifford said.

Such work eventually could lead to “designer foods”--not Calvin Klein’s cookies or Chanel sorbet, but foods in which the good properties are boosted, either by breeding or by adding extracts.

In plants, there are dozens and dozens of molecules called phytochemicals, which work to help the plant survive, said Herb Pierson, a diet and cancer expert who started the Designer Food Project and now works as a consultant. “Those properties may also be conferred to humans when we consume the plant.”

The problem with simply eating food, Pierson says, is that if you analyzed two heads of broccoli, one grown in New Jersey and one in California, “you would see two completely different ‘fingerprints,”’ based on soil, seeds, climate, growing conditions, when the heads were harvested and how they were stored.

So it makes sense, he says, to find the best foods, figure out how they work and infuse other foods with the same properties.

“It’s not so much making a chicken soup to replace penicillin, but making a chicken soup that is better,” Pierson said.

While Wattenberg and Pierson are among those who expect there eventually will be specific diet prescriptions against disease, Woteki is less certain.

“I will be quite surprised if we can single out single foods as either the silver bullets that will cure or prevent diseases or be the causative factors,” Woteki said.

The USDA’s Duke, however, thinks he can do something now. He eats a balanced diet, but adds what he believes is a little extra protection in his “switch from cancer sticks to carrot sticks.”