Hardly a month goes by without a headline trumpeting the news that yet another food has been shown to fight cancer. Broccoli, garlic, onions, green tea, tomatoes, whole grains, even coffee have all joined the anticancer brigade over the years.
So it came as a shock when one of the largest diet and health studies ever undertaken threw cold water on some of those glad tidings. Analyzing data from more than 100,000 people enrolled in the Nurses’ Health Study and the Health Professionals’ Follow-up Study, scientists at Harvard School of Public Health found no link at all between eating fruits and vegetables and cancer risk. It didn’t matter whether people consumed two servings a day or 10; their risk of developing cancer over the 15-year study period was exactly the same.
How could that be? For years, the National Cancer Institute has promoted its “Eat 5 to 9 a Day” program, encouraging Americans to eat more fruits and vegetables. Some of the country’s leading cancer-research centers have published diet books designed to lower cancer risk, featuring fruits and vegetables. Were the experts wrong?
“We’d all like to believe that a healthy diet can help prevent cancer,” says Alice Lichtenstein, D.Sc., a nutrition expert at the USDA Nutrition Research Center on Aging at Tufts University. “Unfortunately, though there appears to be an association between diets high in fruits and vegetables and lower risk of cancer, we have yet to identify exactly which dietary components may be protective, or indeed whether simply upping produce intake may decrease more potentially risky food choices.”
Fiber offers a case in point. Early studies suggested that the more fiber people consumed, the lower their risk of colon cancer. With hopes running high, the National Cancer Institute funded two studies that compared two groups of volunteers, some eating a high-fiber diet, others a diet low in fiber. To universal surprise, the high-fiber diet showed no benefit in reducing risk.
Sharon Ross, a program director at the NCI, remains optimistic that ongoing research will bring better news: “Part of the difficulty is that we don’t have good tools to study diet and cancer,” she says. Many studies are based on what people recall eating over previous years, a notoriously undependable source of information. Animal studies can help, but it’s not easy to know if the results apply to people in the real world. The gold standard is a study that controls what people eat and follows them over time. But because cancer typically takes decades to show up, this kind of study is enormously expensive and difficult to conduct.
Eventually, Ross suspects, scientists may discover that the importance of diet varies, due to genetic differences. “We may find that for some people, eating fruits and vegetables will make a big difference. In others, it may not play much of a role. We’ll be able to tailor dietary advice much more precisely to individuals.”
Wherever research leads, the recent news is no reason to abandon a healthy diet. “There is still a great deal of evidence from many studies that diet can help prevent some cancers,” insists Richard S. Rivlin, M.D., director of the Anne Fisher Nutrition Center at the Strang Cancer Prevention Laboratory in New York. “Prostate cancer is a good example. Precancerous changes occur at the same rate in men almost everywhere around the world, but the progression of the disease is very different. Lots of evidence points to differences in diet as the explanation.”
The American Institute for Cancer Research just published its most up-to-date food, nutrition and activity recommendations to help prevent cancer. Here are 8 quick tips:
1. Be as lean as possible without becoming underweight.
2. Be physically active for at least 30 minutes every day.
3. Avoid sugary drinks. Limit consumption of energy-dense foods (particularly processed foods high in added sugar, or low in fiber, or high in fat).
4. Eat more of a variety of vegetables, fruits, whole grains and legumes such as beans.
5. Limit consumption of red meats (such as beef, pork and lamb) and avoid processed meats.
6. If consumed at all, limit alcoholic drinks to 2 for men and 1 for women a day.
7. Limit consumption of salty foods and foods processed with salt (sodium).
8. Don't use supplements to protect against cancer.
Source: American Institute of Cancer Research
For more information go to www.aicr.org.