Karen Collins, MS, RD, CDN
American Institute for Cancer Research
If you consider fiber as an isolated part of your diet, you may be confused by the results of a recent analysis that looked at over a dozen major studies together. This analysis reported that consuming higher levels of fiber might not protect you from colon cancer. But we don't eat fiber in isolation from other parts of foods. We eat a variety of foods that are higher or lower in fiber, along with their higher or lower levels of nutrients and phytochemicals. Viewed from the broader nutritional perspective, this new analysis doesn't diminish the importance of eating an abundant variety of vegetables, fruits, whole grains and beans and practicing a healthy lifestyle.
Laboratory studies have shown a variety of ways that fiber might lower the risk of colon cancer, but population studies do not consistently support these findings. The new analysis of 13 population studies was an ideal way to find out the dietary effects of fiber, because of the large number of people involved. But its message about dietary fiber is mixed. The people with the lowest daily fiber intake less than 10 grams a day were 18 percent more likely to develop colon cancer, even after a wide range of other influences on colon cancer risk were taken into consideration. However, the analysis did not show any benefit to eating greater amounts of fiber.
Before other factors were taken into consideration, those who ate the most fiber did develop 16 percent fewer colon cancers than those who ate the least. When body weight, activity level, family history and smoking all influences on colon cancer risk were accounted for, a higher fiber consumption still showed some protection. But once researchers figured in people's consumption of red meat, alcohol and folate (a B vitamin), fiber's impact was lost.
The result of this analysis differs substantially from the results of the European Prospective Investigation into Cancer and Nutrition (EPIC) study, which included almost as many people. In the EPIC study, Europeans who ate the most fiber had an almost 40 percent lower risk of colon cancer than those who ate the least. This protective effect persisted even after the influences of activity, alcohol, red meat, smoking and folate were factored in.
When statistical adjustments are done to remove the effect of other influences, like in this analysis of 13 studies, it's hard for scientists to know how much to adjust to determine fiber's effect alone. Cancer research increasingly shows the impact of synergy how two or more factors have more of an effect together than apart. In a Swedish study, women who ate at least four-and-a-half servings of whole grains a day developed 33 percent less colon cancer than women who ate the least whole grains. Obviously, the healthier group ate a lot of fiber, but they also received more of a range of vitamins, minerals and protective phytochemicals.
Whenever you hear about the results of any study, like the recent analysis, it is important to keep in mind that a strong research consensus shows that our diet and lifestyle have a major impact on our likelihood of developing colon cancer. Studies show that when our lifestyle or diet changes even after the age of 30, the risk of colon cancer and the polyps that usually precede colon cancer also changes. While each individual food doesn't produce the same risk or protection in every study, overall we see that diets low in red meat, refined carbohydrates and alcohol, combined with a higher intake of vegetables, fruits, whole grains, beans and fish are linked with the lowest risk of colon cancer. Of course, physical activity and eating appropriate amounts of food to maintain a healthy weight are also important.
You should never pin too much hope on any one part of your diet, like fiber, to keep you healthy. You should also not try to fix a poor diet by loading up on fiber supplements. But the majority of nutrition research shows that the diet linked with a lower risk of colon cancer, heart disease and diabetes is a high-fiber diet.
Reprinted with permission from the American Institute for Cancer Research