How diet affects the odds of cancer is still unknown

By Ridgely Ochs Copyright 1998 Newsday December 1, 1998

Despite all the hoopla and fervid research in the area, what precise role diet plays in causing or reducing breast cancer, or all cancers, is simply not clear yet, experts say.

"If people ask me now what kind of diet they should eat, I tell them they should eat a heart-healthy diet from the American Heart Association," said Dr. John Glaspy of the UCLA Comprehensive Cancer Center.

Glaspy, whose work looking at whether fish oil may reduce the risk of breast cancer is prominently quoted in television doctor Bob Arnot's "The Breast Cancer Prevention Diet," said he is very sure diet does play a role in cancer. But, he said, "I don't want them people to think we have the answers."

"I hold these truths to be self-evident: This area is clearly of the utmost importance for cancer research. There's evidence from the epidemiology of breast cancer that up to 80 percent may be preventable, and it is very likely if there is a prevention, it is rooted in some form of nutritional intervention," Glaspy said. "Here's what we don't know: We don't know what in the diet is the major driver of breast cancer."

Dr. Moshe Shike, director of the cancer prevention and wellness program at Memorial Sloan-Kettering Cancer Center in Manhattan, agrees. "Diet and cancer is a very complex issue. We cannot simply tell you what to eat and tell you that is going to prevent cancer. We know some things with regard to diet that may reduce risk and the emphasis is on 'may. "

Arnot's book, which promotes the use of fish oil, flaxseed and soy products to prevent breast cancer, has stirred a hornet's nest of controversy. Fran Visco, head of the National Breast Cancer Coalition, called the book "unbelievably irresponsible" and said it "misrepresents the science and misleads women. It is not harmless." Celeste Torell, a spokeswoman for the American Cancer Society, said there isn't enough scientific evidence to recommend a diet to prevent breast cancer, although there are broad guidelines that may to help reduce the risk of all cancers. "Why give false hopes?" she said. And one of the researchers featured in the book, Dr. Lilian Thompson at the University of Toronto, said Arnot has overstated her research, which has been completed in animals and not in humans. Arnot, who calls the diet "a bet made on a sound analysis of all the current nutritional research," has vigorously defended the book.

In the midst of this, a study was published in the Journal of the National Cancer Institute that found that women who eat beef and bacon cooked until very well done had more than four times the risk of breast cancer compared with those who eat rare meat. Cooking meat at a high temperature, by frying or grilling, produces carcinogenic agents, heterocyclic amines, linked to colon and stomach cancer, but not previously linked in large human studies to breast cancer.

Although a fairly large study, with 930 people, and published in a prestigious journal, the study illustrates how hard it is to determine the relationship between diet and cancer. It also points out why people should not suddenly change diet based on one study.

The study asked 273 breast cancer patients to rate their preference for meat doneness on a scale of 1 to 9, with 9 being the most done, compared with a group of healthy women. This raises a major problem with "recall bias," the possibility that facts were misremembered or overstated, said Kathleen Egan of the Harvard School of Public Health, who wrote an accompanying editorial.

What's more, the study didn't find an association between how well done chicken and fish were cooked and breast cancer, although some studies have found these to contain among the highest levels of heterocyclic amines, Egan said. The women weren't asked about chicken and fish, said the lead researcher, Wei Zheng of the University of South Carolina School of Public Health. "This was one of the mistakes in the study," he said.

Finally, the study showed an association of breast cancer with the preference for well-done meat, not with the actual consumption of the food, she said.

The bottom line, both Egan and Zheng said, is that while the study may open up important avenues of research, we should not change our diets based on this one study. Or any one study - or book, for that matter.

"The data for diet and reducing the risk of breast cancer comes down strongly on the side of a diet rich in fruits and vegetables," Egan said. Studies have indicated that a high consumption of alcohol - two or more drinks a day - seems to be related to an increased risk of breast cancer, she said. And increased weight in postmenopausal women also seems associated with an increased risk, she said.

But we don't know much else yet for sure. Based on current research, Shike recommends: 1) Don't "overconsume calories." 2) Eat a diet that is no more than 20 percent fat. 3) Eat a minimum of five to eight servings of fruits and vegetables a day. 4) Get at least 25 grams of fiber each day. "A diet like this will be good for the heart, and we cannot tell you for sure that it will prevent cancer, but it may reduce risk," he said.

End of story. Until we know more.

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