Fibre isn’t protective against Diverticulosis

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A colonoscopy-based study was presented at the Digestive Disease Week (DDW) meeting this month which demonstrated that following a high-fibre diet has no protective effect against developing asymptomatic diverticulosis. In fact, the study illustrated that patients who ate more fibre actually had a higher prevalence of the disease.

“In other words, those on a high-fibre diet were 30% more likely to have diverticulosis than those on a low-fibre diet,” said lead author Anne Peery, MD, a fellow in gastroenterology and hepatology at the University of North Carolina in Chapel Hill.

A better understanding of the etiology of diverticulosis would have a great clinical impact. According to estimates from Yale University, about 300 million Americans have diverticula and of those with diverticular disease, between 5% and 20%—or 750,000 to 3 million patients—are symptomatic. Diverticulosis, which costs an estimated $2.5 billion to the US each year, is the second leading cause of gastrointestinal disease in the United States.

Reporter Gabriel Miller states that despite its prevalence, diverticula formation is not well understood. The connection between low-fibre intake and diverticulosis has traditionally been based on decades-old research from the 1970s and early 1980s comparing diverticulosis rates and diet in Western and African countries. Higher fibre intake from fruits and vegetables was believed to protect those in African nations against diverticulosis, which was more prevalent in Western countries. These studies and others were accepted as evidence that diverticulosis was a “fibre-deficiency disease.”

“All of the data to date stand with the observation that dietary fibre is significant and a deficiency is an etiologic risk situation for developing diverticula,” said Martin Floch, MD, clinical professor of medicine in the Digestive Disease and Gastroenterology division at Yale University in New Haven, Conn., who was not involved in the study. “We don’t have any other information to tell us anything different.”

The results of Dr. Peery’s colonoscopy-based study, however, run directly counter to this conventional wisdom because previous studies may have been limited by selection bias, inadequate control of confounders and a failure to accurately and thoroughly diagnose diverticula in the study populations.

For her study, Dr. Peery pooled data from three colonoscopy-based studies done between 1998 and 2010 at University of North Carolina hospitals, each of which collected data on environmental and lifestyle risk factors associated with colorectal adenomas and included information on patients’ diet, physical activity and bowel habits.

The pooled data included 2,104 patients, including 878 diverticulosis cases and 1,226 diverticula-free controls. Dr. Peery controlled for a number of variables, including age, sex, race, body mass index, endoscopist performance as well as use of nonsteroidal anti-inflammatory drugs (NSAIDs), tobacco, alcohol and laxatives.

In a bivariate analysis, patients with diverticulosis were more likely to be older, white, overweight or obese and to use NSAIDs or tobacco. In a multivariate analysis “high-fibre intake was not associated with a reduced prevalence of diverticulosis,” Dr. Peery said.

In fact, patients in the highest quartile of fibre intake, compared with those in the lowest quartile, had an increased prevalence ratio of 1.30 (95% confidence interval, 1.13-1.50; P<0.05).

“This association was dose-dependent,” Dr. Peery said. “With each increasing quartile you see increasing prevalence.”

Investigators also found that for patients with less than two diverticula, fibre did not play a role; however, in patients with high total dietary fibre intake, there was an increased prevalence of three or more diverticula. Fat and red meat intake and physical activity level had no association with diverticulosis.

“A high-fibre diet is associated with a higher, not lower prevalence, of asymptotic diverticula, and this association is both dose-dependent and stronger when limited to cases with three or more diverticula,” Dr. Peery concluded. Given these results, previous hypotheses regarding diverticulosis risk factors and diet recommendations should be reconsidered, Dr. Peery said.

Dr. Floch, a leading expert on diverticulitis who lectured on the subject at the DDW meeting, called the study “very provoking,” but said that “the data presented are inadequate to determine whether the conclusions are right or wrong. What the authors present is provocative, but we have to see more than that,” Dr. Floch concluded.