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Study Questions Prevailing Wisdom About Fiber, Diverticulosis
By Salynn Boyles
WebMD Health News
Reviewed by Laura J. Martin, MD
Jan. 23, 2012 -- A new study challenges the long-held belief that a high-fiber diet prevents the formation of small pouches in the colon wall that can lead to diverticular disease.
For decades, doctors have recommended high-fiber diets to patients at risk for developing the intestinal pouches, known as diverticula.
The thinking has been that by keeping patients regular, a high-fiber diet can keep diverticula from forming. But the new study suggests the opposite may be true.
Fiber Eaters Had More Pouches
People in the study who ate the least fiber were less likely to develop the pouches than people who ate the most.
Another surprise: Constipation was not associated with a higher risk of having diverticulosis, which had also been a long-held theory behind the disease. Diverticulosis is a condition in which multiple pouches form in the wall of the large intestine.
"Our study makes it clear that we don't really understand why diverticula form," says researcher Anne F. Peery, MD, a fellow in gastroenterology at the University of North Carolina School of Medicine at Chapel Hill.
"There are a lot of good reasons to eat a high-fiber diet, and this study doesn't change that," she says. "But it may not protect people from developing diverticula."
Pouches May Lead to Diverticulitis, Other Complications
About half of Americans will have diverticula by the age of 60, and two-thirds will develop the pouches on the walls of their large intestine by age 85, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).
Many experience no symptoms, but 10% to 25% develop diverticulitis -- a potentially serious condition that occurs when the pouches become inflamed.
Diverticula can also lead to other potentially life-threatening complications, including infection and bleeding. According to one report, diverticular disease caused more than 300,000 hospitalizations and nearly 3,400 deaths in the United States in 2004 alone.
Although a low-fiber diet has long been implicated in the formation of diverticula, there is almost no scientific evidence to back up the association, Peery says.
This is also true for other suggested risk factors for diverticular disease, including eating a high-fat diet or a diet high in red meat, being physically inactive, and having frequent constipation.
In an effort to better understand the impact of these suspected risk factors on the formation of diverticula, Peery and colleagues from the University of North Carolina and the Albert Einstein College of Medicine in the Bronx recruited more than 2,100 adults between the ages of 30 and 80 for their study.
Fiber, Constipation, Red Meat Off the Hook?
All the participants had colonoscopies to confirm or rule out the presence of diverticula, and all were interviewed regarding their diets, bowel habits, and activity level.
Among the surprising findings:
- People with the lowest fiber intake were 30% less likely to develop diverticula than people whose diets included the most fiber.
- Constipation was not associated with an increase in risk. In fact, people who had more than 15 bowel movements a week were 70% more likely to develop the pouches than those who had fewer than seven a week.
- Neither lack of exercise nor eating a diet high in fat or red meat appeared to increase the risk for diverticula.
The study appears in the February issue of the journal Gastroenterology.
Expert: 'Look Elsewhere for Cause'
Researcher Lisa L. Strate, MD, MPH, of the University of Washington School of Medicine in Seattle, called the study "important and provocative."
Strate's own research, published in 2008, also turned conventional wisdom about diverticular disease on its head, finding no merit to the prevailing wisdom that patients at risk for diverticulitis should avoid nuts, corn, and popcorn.
"We have been stuck on the idea that fiber is a major player in diverticular disease for too long without really being able to back it up," she says. "This study tells us that we need to look at other potential risk factors."
Digestive disease specialist David Bernstein, MD, agrees. Bernstein is chief of the division of gastroenterology at North Shore University Hospital in Manhasset, New York.
"This is a very important paper that questions what has been our dogma," he says. "We now have scientific evidence that does not back up what we have been telling people."
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