A diet rich in fruits and vegetables is important for one’s digestive health. But researchers at the UNC School of Medicine have found reason to question this long-held belief when it comes to an intestinal disorder called diverticulosis.

Diverticulosis is a condition wherein outpouchings develop in the colon because of weakness in the muscles lining the intestinal wall. Millions of people, including about one-third of adults over age 60, may have diverticulosis and not even know it. People who have the disorder can develop diverticulitis, an infection of these outpouchings. Diverticulitis can cause serious complications ranging from abdominal pain and flu-like symptoms to bleeding, and in some cases, even death. It is often treated with antibiotics. A patient who has three or more episodes of diverticulitis usually must have a colectomy, a surgical procedure to remove all or part of the colon.

Scientists’ long-standing belief has been that a diet high in fiber-rich foods helps to prevent and treat diverticulosis, says Suzanne Havala Hobbs, an expert in health and nutrition at UNC. But researcher Anne Peery and her colleagues found that the studies supporting these claims have problems. Some of the studies have selection bias: the researchers in the study were directly involved in interviewing and assessing the patients. In some of the studies, patients weren’t properly assessed to make certain whether they had diverticulosis. And many of the risk factors associated with diverticulosis, including a low-fiber diet, low physical activity, and high meat intake, were based on evidence from only a handful of studies.

To determine whether diet and other factors contribute to developing diverticulosis, Peery and her colleagues studied over 2,000 patients who had undergone colonoscopies at UNC. In addition to having the patients’ medical histories and colonoscopy results, the researchers had detailed information about how much the patients exercised and what they ate.

Peery found that the patients who had a high-fiber diet were 70 percent more likely than those with a low-fiber diet to have diverticulosis. “We were all taught in medical school that a low-fiber diet causes small, hard stools, and there’s retraction, and all that pressure causes diverticulosis,” Peery says. “Our study shows that we should step back and rethink our assumptions about diverticular disease.”

Peery and her colleagues are now following up their study with more detailed research into the causes of diverticulosis, which are still unknown. There is preliminary evidence that bacteria in our gut may play a role in the development of the disorder.

Will these findings affect the current dietary recommendations for patients at risk for diverticulosis? “No, not right now,” Peery says, “and that’s okay.” Many more patients need to be studied to really pinpoint the cause or causes of diverticulosis, she says.

Countless reputable studies have demonstrated a clear role for dietary risk factors such as cholesterol, added sugar, and alcohol in the development of complications such as heart disease, stroke, and cancer. The purpose of studies such as Peery’s is not to undermine the research done by thousands of highly skilled, highly trained professionals; it is simply to gain better insight into our problems. “The literature is not always as good as you think it is, and what you’re doing may not be as evidence-based as you thought it was,” she says. “But that’s the great thing about being in an academic setting: you get to rethink all of those things.”

Despite the implications of Peery’s findings, we should not dismiss fiber-rich foods altogether, because they can be beneficial, Hobbs says. “A diet high in fiber-rich foods is still the standard of practice for being generally health-supporting and helpful in the prevention and treatment of a wide range of diseases and conditions,” she says. “But it’s important to keep an open mind. What we know about the relationship between diet and health improves over time.”