For years we've known that a good weight, a good diet and exercise can help men and women keep their hearts healthy. But cancer? That seemed to be a disease over which we had little control.

Now, emerging science is telling us that weight, diet and exercise play a crucial role in protecting us against cancer, too. Indeed, there are lifestyle changes we have the power to make that will improve our odds against this disease, researchers say.

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Eat the right foods to reduce your cancer risk. — Renée Comet

"We know that we can prevent about a third of all cancers if people would maintain a healthy weight, eat a plant-based diet and be physically active," says Alice Bender, a registered dietitian with the American Institute for Cancer Research (AICR).

If you don't smoke, controlling your weight is the most important thing you can do to reduce your risk of cancer. More than 100,000 cases of cancer a year could be prevented in the United States if people maintained a healthy weight, the AICR estimates.

"Dozens and dozens of studies show that people who are overweight or obese have higher rates of many different cancers," says Walter Willett, M.D., head of the department of nutrition at the Harvard School of Public Health. "It's not just one study or two," he says. There is "a massive amount of evidence."

One groundbreaking study by the National Institutes of Health — following more than half a million AARP volunteers age 50 and older beginning in 1995 — has looked at how diet influences health, especially connections between diet and cancer. Albert Hollenbeck, senior research adviser for AARP, helped coordinate the study's volunteers. He says the long-running NIH-AARP study has given us the strongest evidence to date of links between diet and cancer in older Americans.

In the study, people who ate plenty of vegetables, beans, fruits, nuts, whole grains, olive oil and fish — and less red meat, processed meat and butter — had fewer cases of cancer and heart disease, says Rashmi Sinha, deputy chief of the Nutritional Epidemiology Branch at the National Cancer Institute.

The NIH-AARP study has yielded dozens of important scientific papers. Looking at large groups of people for years, the researchers found associations between the foods the participants ate and their health. In August, for example, they reported that women who drank more than three cups of coffee a day were 35 percent less likely to be diagnosed with endometrial cancer. While the apparent link between coffee and this cancer is intriguing, until scientists understand how coffee works on this disease, they won't have absolute proof of its protection. But what we do have are strong indications that some foods can affect our cancer risk.

Next: Carcinogens in meat. »