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There Is No Magic Diet That Will Prevent Breast Cancer

Health: A new book may mislead women. Obesity is the only proved dietary link.

November 19, 1998|HENRY I. MILLER | Henry I. Miller, a physician, is a director of the American Council on Science and Health and a fellow at Stanford University's Hoover Institution. E-mail:

Actors who play doctors on TV are sometimes mistaken for the real thing. In a bizarre turnabout, Dr. Bob Arnot, a real physician and NBC-TV's chief health correspondent, has written a book worthy of someone without medical training. "The Breast Cancer Prevention Diet" is so fraught with unscientific, speculative and misleading advice that it may actually be harmful to women's health.

A study by the National Health Council found that adults cite television as their "principal source of health information" and often look to doctors in the media as reliable sources, so the deficiencies of Arnot's book are particularly distressing. He claims, for example, that certain foods can prevent breast cancer, but most studies have found little if any relationship between diet and breast cancer when the effects of obesity are eliminated.

Arnot encourages the consumption of soy and flaxseed, which supposedly work by competing with estrogen for receptors on breast cells, because they are "safer natural alternatives" to drugs known to prevent breast cancer for certain individuals. While it is true that certain foods do appear to block estrogens, which have a role in many breast cancers, it is far from proved that this effect reduces cancer in humans. Arnot's statement that intake of such foods "can save your life" is a gross overstatement of the scientific evidence.

Arnot asserts that synthetic chemicals called xenoestrogens sometimes found in the environment act as "super estrogens," and that they thereby increase the risk of breast cancer. But there is no evidence for this, and Arnot's theorizing ignores the far more important role of the body's own more potent estrogens, such as estradiol.

Arnot claims that "alcohol consumption is the most solidly established dietary factor related to cancer of the breast and one of the most powerful." Therefore, he recommends abstaining from alcohol but advises, "If you do drink, organic products, such as champagne, wine, beer, tequila and vodka, are clearly the safest, since they have the least risk of contamination or carcinogens." The role of alcohol intake as a risk factor in breast cancer is unproved. If it were a significant risk factor, however, women should abstain from alcohol altogether.

Arnot's claims about vitamin D are inconsistent and problematical. He writes that it "is a potent inhibitor of a cell's ability to divide and grow. Vitamin D also helps breast cells to become more mature so they are less vulnerable to cancer-causing toxins." Yet he admits that "there is no evidence that vitamin D supplement has any effect on breast cancer rates." Nevertheless, he recommends taking it, in spite of known toxicity at high levels.

Arnot characterizes foods as being, in effect, drugs without side effects. But the unconventional choices and amounts of foods in his suggested diet may instead be tantamount to ingesting drugs without adequate testing.

By diverting women from important actions and diagnostic procedures that are known to be lifesaving, Arnot distorts the valuable message that women should take control of their breast cancer risk. Some known risk factors--genetics, a history of benign breast disease, onset of menses before age 12, menopause after age 50--are beyond an individual's control. But others, such as little exercise, post-menopausal estrogen replacement and post-menopausal obesity, can be controlled. And women should be aware of well-established ways to detect breast cancer early, including self-examination, routine physician examination and mammography.

The public has been bombarded with messages urging substantial dietary changes to reduce the risk of cancer. Americans have been led to believe that the link between specific dietary factors and cancer is solid and convincing and that dietary modification should be the top priority in cancer prevention. The truth is that the cessation of smoking is the single most important factor in cancer prevention. There is no dietary change that will counteract the harmful effects of cigarette smoking.

Diet is not wholly irrelevant, however. A substantial body of evidence associates low intake of fruits and vegetables with increased risk of cancer. It would be wise for all people, therefore, to make an effort to include fruits and vegetables in their daily diets. But the current scientific evidence does not warrant the kinds of drastic dietary changes advocated by Arnot.

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