Fruits and Vegetables Can't Thwart Cancer

Extolling the virtues of fruits and vegetables has become every foodie’s favorite pastime, and government health organizations typically recommend between 5-9 servings a day to ward off cardiovascular disease, lower cholesterol, improve brain function, regulate mood, prevent diabetes, and reduce cancer risk. A diet rich in rabbit food may have negligible anti-cancer effects, however, according to a large, high-profile study published in the current issue of the Journal of the National Cancer Institute.

Researchers examined the eating habits and rate of cancer incidence of 142,605 men and 335,873 women in 10 European countries from 1992 to 2000. Estimated risk was adjusted for variables strongly linked to cancer, such as smoking and alcohol consumption. Participants who increased their intake of fruits and vegetables by 200 grams a day—about 2 servings, or 1 large apple—reduced their risk of cancer by approximately 4%. Although the benefits were marginally stronger for heavy drinkers, the authors of the study called the overall link “weak,” and advised caution in applying it to dietary recommendations.

According to CNN, the study’s lead author, Paolo Boffetta, MD, said the results should not discourage people from increasing their intake of foods that provide a host of other confirmed benefits. “This doesn’t mean fruits and vegetables aren’t important,” he said. Boffetta also emphasized the complexity of cancer, diet, and the relationship between the two.

Limitations built into the study may explain its standout results, which differ drastically from similar research conducted in the 1990s that suggested risk reductions as high as 50%. In an editorial published with the report, Walter C. Willett, MD, DrPH, of the Harvard School of Public Health’s Department of Nutrition, notes that the study did not examine the benefits of specific types of fruits or vegetables. For example, a separate study found “considerable evidence” that lycopene—a nutrient present in tomatoes—was protective against prostate cancer, Willet wrote.

He also points out the errors inherent in self-reported data, especially when it concerns participants’ diets. Furthermore, the study’s 9-year span focused on adulthood, rather than childhood, during which “antioxidants or other protective constituents of fruits and vegetables may need to be present” in order to significantly impact cancer risk, Willet said.

The results of the study, published April 6, 2010, are available on the Journal of the National Cancer Institute's Web site.