Eat More Beans to Prevent Colon Cancer
July 13, 2006—Will eating more fruits and vegetables protect against colon cancer? Most people would probably say yes. But while recent large studies have shown no link between eating fruits, vegetables, or legumes and the risk of colon and rectal cancer, new research has found that people who eat more dry beans—such as pinto beans, navy beans, lentils, and bean soups—have significantly less risk of developing colon cancer.
“Colorectal cancer is the second leading cause of cancer death in the United States,” said Elaine Lanza, PhD, head of the Colon Cancer Prevention Group at the National Cancer Institute and lead author on the study. “Data we culled from the Polyp Prevention Trial suggests that adding a significant amount of dry beans to one’s existing diet has a strong protective effect against recurrence of precancerous polyps.”
The Polyp Prevention Trial is a multicenter randomized clinical trial designed to determine the effects of a high-fiber, -fruit, and -vegetable and low-fat diet on the recurrence of precancerous polyps in the colon (advanced colorectal adenomas).
The trial included 2,079 men and women over age 35 who had precancerous polyps in the six months prior to the study. They were questioned extensively throughout the study about their diets. Over a four-year period, many people changed their diets to include more of the foods they thought would prevent a recurrence of their polyps. The largest increase in fruit and vegetable intake was in dry beans, which tripled.
Those who added the most dry beans to their diets (compared with those who added the least) had a significantly reduced risk for recurrence of advanced polyps. On average, these people increased their dry bean intake nearly fourfold (370%).
Few studies have examined dry beans as a separate category, which has made it difficult to interpret the relation between dry beans and colon cancer. Many studies lump all legumes together, including dry beans, dry peas, green peas, green beans, lentils, soybeans, peanuts, and alfalfa sprouts. These foods have diverse nutrient compositions and differing amounts of protective constituents. The new research gives added reason to specifically examine the protective constituents in dry beans.
Dry beans contain a wide range of nutrients and other active constituents that may protect against cancer. The nondigestible carbohydrates in dry beans are fermented in the colon by normal bacteria and are converted into a short-chain fatty acid called butyrate, which has demonstrated anticancer and anti-inflammatory activity. Dry beans also provide a kind of carbohydrate that raises the blood sugar level slowly, rather than quickly, an effect that has been associated with lower risk of colon cancer. Other components in dry beans have cancer-fighting properties as well. These include saponins, inositol hexaphosphate (phytate), gamma-tocopherol (a form of vitamin E), and phytosterols. It is also possible that the combined action of several different constituents of dry beans is responsible for the reduced cancer risk.
“This is the first reported protective association between dry bean intake and advanced polyp recurrence, and more research is needed.” said Dr. Lanza. “In addition to containing a wide range of nutrients and constituents that may be protective against cancer, we already know that dry beans are naturally low in fat, contain no saturated fat or cholesterol, and provide important nutrients such as fiber, protein, folic acid, calcium, iron, and potassium. USDA guidelines call for Americans to consume at least 3 cups of beans per week—that’s six times the current consumption for most people.”
(J Nutr 2006;136:1896–903)
Jeremy Appleton, ND, CNS, is a licensed naturopathic physician, certified nutrition specialist, and published author. Dr. Appleton was the Nutrition Department Chair at the National College of Naturopathic Medicine, has served on the faculty at Bastyr University of Natural Health Sciences, and is a former Healthnotes Senior Science Editor and a founding contributor to Healthnotes Newswire. He has worked extensively in scientific and regulatory affairs in the supplement industry and is now a consultant through his company Praxis Natural Products Consulting and Wellness Services.
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