Does Diet Affect Cancer Recurrence?
Reviewed by Faculty of Harvard Medical School on February 24, 2010
By Stephanie Meyers, M.S., R.D., L.D.N.
This past July, the latest results of The Women's Healthy Eating and Living (WHEL) trial were published in The Journal of the American Medical Association (JAMA). The study of 3,088 women concluded that eating more fruits, vegetables and fiber while eating less fat did not reduce a woman's risk of breast cancer recurrence or death. Yet just two years earlier other data from WHEL showed that women who had the highest levels of carotenoids in their blood (a biomarker for fruit and vegetable intake) lowered their chances of breast cancer returning by 43% compared with women with the lowest levels of carotenoids in their blood.
How can one study generate such different results? Does eating more fruits and vegetables offer any potential benefit for cancer survivors? It's not surprising that many cancer survivors feel confused about what they can do to reduce their risk of cancer coming back. In the words of one cancer survivor, "Will eating fruits and vegetables actually make me live longer or is it just going to feel like it?!" Here's how to make sense of the conflicting WHEL results and some tips for staying cancer-free.
The JAMA study published on July 18 compared two different groups of WHEL participants. The first group received telephone counseling, cooking classes and newsletters promoting a low-fat diet and eating 8 to 10 servings of fruits and vegetables a day. The second group of women received written materials from the "5-A-Day" program, which encouraged them to aim for five servings of fruits and vegetables a day.
The researchers found that the women who were eating approximately 8 to 10 servings of fruits and vegetables a day had the same risk of their breast cancer returning and dying from breast cancer as the women who were eating approximately 5 servings a day. While this suggests that eating more than 5 servings of fruit and vegetables a day may not affect breast-cancer survival, it definitely should not be interpreted as meaning that fruits and vegetables do not play a key role in preventing chronic diseases, such as heart disease and cancer.
It's worth noting that the group of women eating 8 to 10 servings of fruits and vegetables a day did not meet their target goal for reducing fat intake, although they did eat less fat than the other group. This may explain, at least in part, the lack of difference between the two groups.
The 2005 WHEL study was a different type of study and less rigorous than the recent one. It evaluated just the women in the 5-A-Day group. There was no "control" group or intervention being tested. The researchers grouped the women according to levels of carotenoids in their blood, ranking them from highest to lowest. The women with the highest levels of carotenoids had 43% lower chance of breast cancer recurrence or death when compared with women with the lowest levels of carotenoids in their blood.
These studies are far from the final word on how a diet rich in plant-based foods may influence cancer recurrence. Researchers continue to explore the connection bewteen diet and cancer recurrence, with new reports being published all the time. A study reported in JAMA August 15, 2007 suggests people who eat a "Western" diet red meat, high fat, refined grains and dessert have a higher chance of their colon cancer returning than those who consume a "prudent" diet consisting primarily of fruits, vegetables, poultry and fish.
It's important not to misinterpret the message from the WHEL study because eating fruits and vegetables is still one of the best choices you can make for overall health. The fact remains that Americans on average eat only 2.5 servings of fruits and vegetables each day, well below the recommended level!
In fact, the most current research on cancer survivorship addresses the importance of weight management. Diets rich in fruits and vegetables are one of the primary ways to reduce the risk of overweight and obesity, which are direct risk factor for many types of cancer. In addition, eating lots of fruits and vegetables decreases your risk for cardiovascular disease, hypertension and other causes of death. Reducing risks for these health problems is very important for cancer survivors. So one of the first steps a cancer survivor can take is to at least meet the 5-A-Day recommendations. (The Centers for Disease Control and Prevention replaced the 5-A-Day program with Fruits & Veggies-More Matters campaign.
Here are some other tips for cancer survivors to increase their likelihood of remaining cancer-free.
When it comes to cancer survivorship it is important to remember that it's not just one factor (like fruit and vegetable intake), that is likely to make the difference. The most powerful protective effect is likely a combination of lifestyle factors, including diet and physical activity.
Stephanie Meyers, M.S., R.D., L.D.N. received her master's degree in nutrition and health promotion from Simmons College, Boston. She is a senior clinical nutritionist at Dana-Farber Cancer Institute and Brigham and Women's Hospital.