Healthy Diet May Not Vanquish Breast Cancer

Contrary to past research, a healthy diet may not prevent breast cancer.


July 17, 2007&#151; -- There are many things a breast cancer survivor can do to keep her cancer at bay -- but eating a diet that is high in fruits and vegetables isn't one of them, new research suggests.

But cancer experts not affiliated with the study were quick to react to the findings, fearing that the new research would discourage breast cancer survivors from pursuing a healthy diet -- a dangerous move, in their opinion.

In the study, released Tuesday in the Journal of the American Medical Association, researchers at the University of California, San Diego enrolled more than 3,000 breast cancer survivors.

Half the women studied ate five or more servings of fruits and vegetables per day, as is recommended by the U.S. Food and Drug Administration. The other group of women ate five servings of vegetables plus three servings of fruit, along with 30 grams of fiber every day. They also reduced their fat intake to 15 to 20 percent of their daily caloric intake; Americans generally get 30 to 40 percent of their calories from fat.

After seven years, the women who reported eating a superhealthy diet appeared to be no more likely to be cancer-free than the women who ate just the healthy diet.

Even the researchers were somewhat surprised by what they found.

"What really surprised us was the absolute lack of difference between the groups," says lead study author John Pierce of the Cancer Prevention and Control Program at UCSD.

"The lines [of cancer recurrence] were just literally on top of one another, and we were not expecting that."

The study's results seem to directly contradict a study last year that showed that breast cancer survivors who ate a low-fat diet reduced their risk of a repeat cancer diagnosis.

There are a number of reasons why the study may have found what it did. For one, the women were self-reporting their eating habits -- possibly leading to dubious results.

"People ate less toward the end [of the study]," says Keith Ayoob, associate professor of pediatrics at Albert Einstein College of Medicine. "But they either didn't lose weight or actually gained weight. This puts a bit of strain on the credibility of the self-reporting."

And even if the women reported their calories accurately, most of them did not reach the target fat reduction in their diets -- even after receiving counseling and other interventions.

"These women did not reduce their dietary fat very much by their self report," says Dr. Dean Ornish, founder and president of the Preventive Medicine Research Institute in Sausalito, Calif.

"Both groups reported consuming more fat at the end of the study than at the beginning, so the hypothesis could not be tested."

Also, the women in this study were already eating more fruits and vegetables than most Americans, even before the study started.

"The study utilized women who were already using far greater amounts of fruits and vegetables than most individuals -- one serving of fruit and two of vegetables is the norm," says Elizabeth Jeffery, professor of nutrition at the University of Illinois at Urbana.

This could minimize the amount of difference between the groups, since both were eating healthy diets at the start.

Critics of the study also urged that the results must be viewed in perspective with other, similar studies.

For example, a previous report by the same group, published in June 2007 in the Journal of Clinical Oncology, showed that diet made a big difference in reducing breast cancer mortality.

There is another point of view in the diet and cancer world: Perhaps everything that we think is good for us is actually bad.

"Good food causes cancer," says Dr. David Jenkins, professor of nutritional sciences at the University of Toronto.

"Let me explain the hypothesis: Cancers also feed on good foods," he says. "So giving cancer lots of calcium, omega-3 fatty acids, folic acid, and so on can actually help it grow."

Dr. Jenkins believes that the way out of the good-food-causes-cancer quagmire is to reduce the amount of calories we take in -- drastically.

"The solution is not cherry-picking good foods," he explains, "but choosing things that have anti-nutritive values, and keeping your calories low. If you eat 20 percent fewer calories, then you are truly lean and mean. You're also lean and mean as an environment for tumor growth."

But the worst solution to this problem, Jenkins says, is to switch over to a junk-food diet.

"Good food will kill you," he says. "But bad food will kill you quicker."

Outside of an extreme diet, there are other factors that may reduce both the risk of cancer's first time occurrence, as well as its recurrence.

"The strongest influence on risk of first occurrence of breast cancer is diet at the time breasts are developing -- that is during puberty," says Carla Wolper, of the Obesity Research Center at St. Luke's Hospital in New York City.

"A healthy body weight and low to moderate fat intake during puberty, particularly a diet low in animal fat, is recommended."

Even if women can't go back in time to rescue their eating habits in their teenage years, there are still things they can do today to reduce the risk of breast cancer.

"A healthy diet needs to be a marathon, not a sprint," says Ayoob, who recommends a diet high in fruits, vegetables , and whole grains, along with a focus on low-fat and fat-free dairy foods.

"I also want [my patients] to be a healthy weight and exercise daily," he says. "I want my patients to have a decent shot at preventing cancer recurrence, but they shouldn't have to trade cancer survival for heart disease."

Other experts agree that a long-term view is the best one to take.

"Consider, as an analogy to cancer prevention, fire prevention," says Dr. David Katz, director of the Prevention Research Center at the Yale University School of Medicine.

"So, for example, not smoking -- or having a smoke detector -- would be useful fire prevention strategies. But not smoking, or having a fire detector, would do nothing to help put a fire out! And neither would do much to prevent the recurrence of a fire that had not been put out altogether, either."

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