ATLANTA (AP) — A cancer diagnosis often inspires people to exercise and eat healthier. Now the experts say there’s strong evidence that both habits may help prevent the disease from coming back.

New guidelines issued Thursday by the American Cancer Society urge doctors to talk to their cancer patients about eating right, exercising and slimming down if they’re too heavy.

That’s not something most doctors do, said Dr. Omer Kucuk, an Emory University oncologist who has researched the effect of nutrition on prostate cancer. They’re focused on surgery, chemotherapy or other treatments for their patients, he added.

“Usually the last thing on their mind is to talk about diet and exercise,” Kucuk said.

Cancer society officials have long encouraged healthy eating and exercise as a way to prevent certain cancers. They and others have tried to spread that gospel to cancer survivors as well. Indeed, the cancer society has a certification program for fitness professionals who work with cancer survivors.

Strong statement

But until now, the group didn’t think there was enough research to support a strong statement for cancer survivors.

Hastine Reese, a breast cancer survivor, says she began to exercise because her husband — not her doctor — pushed her. Besides being good for her health, he thought it might help pull her out of the depression that followed her diagnosis and double mastectomy.

“When you’re first diagnosed with cancer, you go into a dark place,” said Reese, as she finished a one-hour exercise class this week at DeKalb Medical Center in Decatur, Ga.

Exercise has changed that. “I’m coming into the light, and it’s getting brighter and brighter,” she said.

Being overweight or obese has long been tied to an increased risk of several types of cancer, including cancers of the colon, esophagus, kidney, pancreas and — in postmenopausal women — breast. But there hadn’t been much evidence on the effects of diet and exercise for people who had had cancer.

More than 100 studies

The last five years saw more than 100 studies involving cancer survivors, many of them showing that exercise and/or a healthy diet was associated with lower cancer recurrence rates and longer survival.

Most of the research was on breast, prostate and colorectal cancer. The evidence is more meager when it comes to other cancers, including the deadliest kind, lung cancer. Also, most of the work involved observational studies, which can’t prove a cause and effect. Still, the volume of research was compelling.

“We’ve got enough data now to make these recommendations,” said Colleen Doyle, the organization’s director of nutrition and physical activity.

At least two other medical groups have strongly recommended exercise and healthier eating for cancer survivors, but the cancer society’s new guidelines are expected to have much greater impact. It’s the nation’s largest cancer charity in both donations and the number of volunteers, and it funds more cancer research than any other non-governmental agency.