No link between eating fruits and vegetables and a subsequent decreased risk for breast cancer

Contrary to findings in previous studies, new research that includes a large group of women found no link between eating fruits and vegetables and a subsequent decreased risk for breast cancer, according to a study in this week’s JAMA.

Carla H. van Gils, Ph.D., of the University Medical Center, Utrecht, the Netherlands and colleagues examined how the intake of total and specific vegetable and fruit groups is related to breast cancer risk among participants in the European Prospective Investigation Into Cancer and Nutrition (EPIC) study, a large prospective collaboration project carried out in 10 European countries. This project, currently including 519,978 individuals, is the largest ever conducted specifically to investigate the relationship between diet and cancer. It includes participants living in countries from the north to the south of Europe, spanning a wide range of vegetable and fruit consumption.

For this study, the researchers examined data from 285,526 women from this group between the ages of 25 and 70 years. Participants completed a dietary questionnaire in 1992-1998 and were followed up for incidence of cancer until 2002.

During follow-up, 3,659 invasive incident breast cancer cases were reported. The researchers found no significant associations between vegetable and fruit intake and breast cancer risk. For 6 specific vegetable subgroups no associations with breast cancer risk were observed either.

“This absence of a protective association was observed among almost all of the participating countries. A protective effect is supported by a vast number of case-control studies. It is possible, however, that the inverse relationships reported from case-control studies may have been overstated, because of recall bias and possibly because early symptoms in patients may have led to a change in dietary habits. In addition, selection bias is a problem in situations where control participation is less than complete because those controls who participate are likely to be more health conscious and consume greater amounts of vegetables and fruits,” the authors write. “The advantages of our cohort study are its size and the wide range of vegetable and fruit intake, caused by the inclusion of participants living in countries from the North to the South of Europe.”

“… the findings from this study confirm the data from the largest pooled analysis to date, in that no large protective effects for vegetable or fruit intake in relation to breast cancer can be observed. This does not exclude the possibility that protective effects may be observed for specific nutrients or in specific subgroups of women, such as those with a family history of breast cancer or estrogen-receptor positive tumors,” the authors conclude.

In an accompanying editorial, Walter C. Willett, M.D., Dr.P.H., of the Harvard School of Public Health, Boston, discusses the studies in this week’s JAMA on diet and cancer risk.

“Although the overall data for red meat and colon cancer are strongly suggestive of an important relation, they are not conclusive. Further studies with long follow-up, repeated measures of diet, genetic markers of susceptibility, more detailed measures of cooking methods, and molecular characterization of colon cancer cases may be helpful.”

“Although recent findings on fruit and vegetable consumption and cancer may be disappointing, reductions in blood pressure and epidemiological evidence for lower risks of cardiovascular disease provide sufficient reason to consume these foods in abundance. The relation between red meat consumption and colorectal cancer may not be conclusive, but prudence would suggest that red meat, and processed meats in particular, should be eaten sparingly to minimize risk.”

“When combined with other healthful diet and lifestyle factors, it appears that approximately 70 percent of colon cancer can potentially be avoided. Replacing red meat with a combination of fish, nuts, poultry, and legumes will also reduce risk of coronary heart disease, in part, because some of these foods have positive benefits. This substitution is an important part of the Mediterranean dietary pattern, which improves blood lipids and other metabolic parameters and has been related to lower rates of total mortality. Thus, keeping red meat consumption low is best viewed, not as an isolated goal, but as part of an overall dietary and lifestyle strategy to optimize health and well-being. Fortunately, substituting pistachio-encrusted salmon and gingered brown basmati pilaf for roast beef with mashed potatoes and gravy is not a culinary sacrifice,” Dr. Willett writes.