People who are diagnosed with cancer or precancer (eg, colorectal polyps) often turn to supplements and other forms of dietary modifications in hopes of improving their prognoses. Although evidence on the effectiveness of dietary modification is limited, many people believe that it cannot hurt, and any potential benefits would be worth it. But some healthcare providers are concerned about the lack of benefit and possible harm that may be associated with such dietary changes .

In a new study published in the July 19, 2006 issue of the Journal of the National Cancer Institute , researchers compiled the results from a group of studies on the effects of dietary modifications for cancer outcomes. They found no clear evidence that dietary modifications evaluated in these studies were associated with improved cancer prognosis.

About the Study

The researchers identified 59 randomized, controlled trials that examined the effects of a variety of dietary modifications in people with cancer or precancerous conditions. The modifications included altering consumption of foods or nutrients through nutrition education or dietary supplements. The researchers compiled the results of the trials to determine the effects of the dietary modifications on the risks of all-cause death, cancer death, cancer-free survival, cancer recurrence, recurrence of precancerous conditions, and progression from precancer to cancer.

Overall, consuming a healthful diet (given as dietary advice or with supplements, weight loss, or exercise) and using antioxidants (eg, vitamins C, E and beta-carotene) or retinal (related to Vitamin A) supplements were not associated with a significant reduction in death from all causes.

Data from three breast cancer trials suggested a reduction in breast cancer death associated with a healthful diet, although the results did not reach statistical significance. Surprisingly, there was some evidence that dietary modifications, including fiber, actually increased the risk of progression from precancerous colorectal polyps to colorectal cancer . However, two trials showed evidence of a reduced risk of recurrence of colorectal polyps associated with calcium supplementation.

This study was limited because the trials investigated a wide range of dietary modifications and cancer outcomes, which made it difficult to get a clear picture of what is going on. Furthermore, it was unclear whether or not most of the trials were of high quality.

How Does This Affect You?

So can changing your diet or taking nutritional supplements help treat cancer or prevent it if you are at high risk? Unfortunately the answer is still unclear. There is evidence of both benefits and risks associated with certain dietary modifications in this study, but there is no convincing evidence that a “healthful diet” significantly improves the prognosis of patients with cancer or precancerous conditions.

While most dietary changes and supplements are probably harmless, this is not true for all of them. Studies have found, for example, that beta-carotene supplements may increase the risk of lung cancer and death in smokers. And it is possible that some dietary modifications may adversely interact with cancer medications.

Before making dietary modifications, talk with your doctor and seek advice from reputable sources, such as the National Cancer Institute. A healthful diet is undoubtedly important for your overall health, but it is not yet certain what role certain modifications may play in the treatment or prevention of cancer.