Eating more fiber tied to lower mortality with colon cancer

(Reuters Health) - People who eat a high-fiber diet or increase their fiber intake after a colon cancer diagnosis may be less likely to die of these tumors than individuals who don’t consume much fiber, a recent study suggests.

“Eating more fiber after colorectal cancer diagnosis is associated with a lower risk of dying from colorectal cancer,” said senior study author Dr. Andrew Chan of Harvard Medical School and Massachusetts General Hospital in Boston.

“This seems to be independent of the amount of fiber eaten before diagnosis,” Chan said by email.

Chan and colleagues examined data on 1,575 adults diagnosed with colon cancer who completed diet surveys detailing how much fiber they ate. They followed half of the participants for at least 8 years. During that period, 773 people died, including 174 who died of colon and rectal tumors.

High fiber diets were associated with lower mortality. Compared to the lowest fiber intakes in the study, each additional five grams of fiber intake was associated with 22 percent lower odds of death from colorectal cancer during the study, as well as 14 percent lower mortality from all causes of death, researchers report in JAMA Oncology.

Changing the diet after the diagnosis to add more fiber was also linked with survival benefits. Each additional five grams of fiber people added to their diets after a colorectal cancer diagnosis was associated with 18 percent lower odds of death from colorectal cancer during the study, as well as 14 percent lower mortality from all causes of death.

The type of fiber mattered, however.

“It appears that cereal fiber and foods high in whole grains seem to be associated with the lowest risk of dying from colorectal cancer,” Chan said.

Each additional 5 grams a day of cereal fiber was linked to 33 percent lower odds of death from colorectal cancer and 22 percent lower odds of mortality from all causes, the study found.

Vegetable fiber wasn’t linked to a meaningful reduction in deaths from colon cancer, but each extra 5 grams a day was associated with 17 percent lower chances of death from all causes.

Fruit fiber, meanwhile, didn’t appear to lower death from cancer or other causes.

The study wasn’t a controlled experiment designed to prove whether or how fiber intake might influence the odds of death from colon cancer, researchers note.

The most important risk factors for colorectal cancer are family history, personal history of polyps/cancer, certain diseases such as ulcerative colitis, and not getting screened, noted Dr. Samantha Hendren, a researcher at the University of Michigan in Ann Arbor who wasn’t involved in the study.

“Lifestyle can also influence risk,” Hendren said by email. “However, diet is only one component of lifestyle risk. Not smoking, being normal weight, and taking aspirin are all associated with lower colorectal cancer risk.”

Even though diet is only one piece of the puzzle, it’s possible that fiber may have beneficial effects on metabolism that may protect against cancer, Hendren added. It’s not clear why patients who already have colorectal tumors would live longer by eating more fiber at that point, however.

Still, eating high fiber foods can lower the risk of getting colorectal cancer or tying from the tumors, noted Nour Makarem, a researcher at Columbia University in New York who wasn’t involved in the study.

“Therefore, consuming a healthy diet that is high in whole grain foods (e.g. brown rice, oatmeal, whole grain cereals or whole wheat bread) and other fiber sources such as fruits and vegetables may protect from colorectal cancer and also improves outcomes and reduces risk of death among colorectal cancer survivors,” Makarem said by email.

SOURCE: JAMA Oncology, online November 2, 2017.