Diet and cancer: little evidence of a direct link

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Screen Shot 2014-04-21 at 1.30.14 PMFor years, if not decades, we ve been hearing that a diet high in fruits and vegetables and low in red meats and fats will prevent various forms of cancer. True? Well, not so much.

As described by George Johnson in his essay in the New York Times aptly titled An Apple a Day and Other Myths the gap between science and wishful thinking is still present, and isn t likely to close soon. Reporting on the annual meeting of the American Association for Cancer Research (AACR), Mr. Johnson noted the dearth of presentations linking dietary intake and cancer prevention. In 1997, by contrast, the AACR reviewed over 4,000 studies and concluded in a massive report that green vegetables helped prevent lung and stomach cancer. Ten years later, the AACR found no benefit for such intake.

What happened in the intervening decade? Mr. Johnson attributes the about-face to better epidemiologic studies. Earlier studies were generally retrospective in nature, relying on individual s recollection of their diets over varying periods of time. Later studies were prospective following people as they aged and obtaining more current dietary intake information. It is these latter studies that indicate that if, indeed, particular foods or types of foods have any impact on cancer causation or promotion, that effect is likely to be weak.

Even Dr. Walter Willett of the Harvard School of Public Health, author of numerous studies on dietary influences on disease, acknowledged that (as quoted by Mr. Johnson) Diet and cancer has turned out to be more complex and challenging than any of us expected.

ACSH president Dr. Elizabeth Whelan had this comment, Perhaps we can now stop demonizing various foods as carcinogenic and concentrate on recommending diets based more on their nutritional value. The strongest link we have between diet and cancer is the link between obesity and various cancers such as uterine and breast cancer. But that s based on excess calorie intake not whether one eats broccoli twice a week.