Fiber probably doesn't protect your colon or rectum against cancer, but it might prevent other digestive woes, such as diverticulosis and GERD.
Experts now believe fiber does not protect against colorectal cancer or constipation. But that doesn’t mean you can cross off high-fiber foods (like vegetables, fruits, and whole grains) from your grocery list. In fact, there are still plenty of reasons -- both digestive and not -- to get your daily fill of fiber.
The results of research studies on fiber consumption and colorectal cancer are mixed. Some show a protective effect, while others show no relationship at all. To add to the confusion, a recent study found a protective effect in men but not in women. Some studies have even reported that a high fiber diet may increase the risk of colorectal cancer.
The theories behind a possible protective effect of fiber on the colon and rectum seemed logical. For instance, fiber may dilute carcinogens in fecal matter, it may help remove carcinogenic bile acids from the body, and it may prompt the body to produce short-chain fatty acids, which help fight off cancer cells. But even if fiber does all of these things, it doesn’t seem to protect against colorectal cancer.
That was the conclusion of a meta-analysis, published in the Journal of the American Medical Association (JAMA). The researchers pooled data from 13 observational studies, containing information on the dietary habits of more than 725,000 men and women who were followed for six to 20 years. During that time, more than 8,000 of them were diagnosed with colorectal cancer.
The study participants were divided into five groups based on their fiber intake. In the initial analysis, those who ate the most fiber had a 16% lower risk of colorectal cancer than those who ate the least fiber. But after adjusting for other risk factors for colorectal cancer -- such as red meat consumption and alcohol intake -- the protective effect disappeared.
Still searching for a link between fiber and colorectal cancer, the researchers examined whether the source of the fiber was important. But neither fiber from cereals nor that from fruits or vegetables had an effect on colorectal cancer risk.
Fiber Probably Won’t Keep You Regular
The JAMA study came on the heels of a review article that dispelled the commonly held belief that fiber helps prevent constipation. While the reviewers don’t deny that increasing fiber intake makes stools bulkier and easier to pass and increases the frequency of bowel movements, they argue that the role of fiber in constipation is exaggerated. In fact, no studies show that a lack of dietary fiber is responsible for chronic constipation. And for some people with constipation, too much fiber can actually make symptoms worse.
