High-Fiber Diet No Help for Diverticulosis

By Charles Bankhead, Staff Writer, MedPage Today MedPage Direct Link
Published: January 23, 2012
Reviewed by Zalman S. Agus, MD; Emeritus Professor
University of Pennsylvania School of Medicine and Dorothy Caputo, MA, RN, BC-ADM, CDE, Nurse Planner

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Action Points

• Risk factors for diverticulosis are typically thought to include a low fiber diet, a high intake of red meat and fat.
• In this study, though, a high-fiber diet did not protect against asymptomatic diverticulosis, and, in fact, was associated with a greater prevalence of the condition.

A high-fiber diet afforded no protection against asymptomatic diverticulosis, findings from more than 2,000 colonoscopy exams showed.
In fact, patients who ate the most fiber had the highest prevalence of diverticulosis, about 30% higher than people who consumed the least dietary fiber.
Moreover, constipation did not increase the risk of diverticulosis -- just the opposite. People who had fewer than seven bowel movements a week had a lower prevalence than those with more frequent BMs.
The findings, reported online in Gastroenterology, confound conventional wisdom about colon health.
"Our data demonstrated no association between fat, red meat, physical activity, and diverticulosis," Robert S. Sandler, MD, of the University of North Carolina in Chapel Hill, and co-authors wrote in conclusion.
"Based on our results, previous hypotheses regarding diverticulosis risk factors and diet recommendations to patients should be reconsidered."
Risk factors for asymptomatic diverticulosis remain poorly defined, although many physicians and patients have considered high intake of dietary fiber and frequent bowel movements as protective, the authors wrote in their background comments.
Studies focusing on the relationship between a low-fiber diet and diverticulosis generally failed to address selection bias and confounding factors and to confirm the presence of diverticulosis, they continued. Similarly, studies of other purported risks -- such as constipation and high consumption of red meat and dietary fat -- have yielded weak supporting evidence.
To learn more about risk factors for asymptomatic diverticulosis, Sandler and colleagues examined data from a colonoscopy-based study that accumulated comprehensive data on diet, physical activity, and bowel habits.
Data for the analysis came from the Diet and Health Studies, which examined environmental and lifestyle factors associated with colorectal adenomas. Participants in three of the studies underwent colonoscopy, most often because of screening indications, family history of colorectal cancer or polyps, or occult bleeding.
The final analysis included 2,104 study participants, 878 of whom had diverticulosis. The remaining 1,226 participants served as a control group.
The authors found that 28% of the diverticulosis group had three or more diverticula, 40% had one or two, and 32% did not have diverticula quantified. Participants with diverticula were more likely to be older, overweight or obese, white, tobacco users, and NSAID users.
An adjusted analysis showed that the prevalence of diverticulosis increased in a linear manner with fiber intake.
Using the lowest quartile of fiber consumption as the reference, the authors found that the odds for diverticulosis increased to 1.03 in the second quartile, to 1.14 in the third, and to 1.30 in the fourth (P=0.004).
Comparing all participants with diverticulosis, the authors found that participants with three or more diverticula were significantly more likely to have the highest intake of dietary fiber (OR 1.81 versus the lowest quartile).
An analysis of the relationship of bowel habits to diverticulosis yielded a similarly linear relationship.
Compared with participants who had fewer than seven bowel movements weekly, those who had seven per week had a diverticulosis odds ratio of 1.34, increasing to 1.59 for eight to 14 weekly bowel movements, and to 1.70 for 15 or more (P<0.001).
Other factors commonly cited as potential risk factors did not have significant associations with diverticulosis, including total fat intake, consumption of red meat, and physical activity.
"We cannot exclude the possibility that people with diverticulosis had symptoms and changed their diet as a consequence," the authors wrote of their findings. "Although such a dietary modification would explain our findings, it is conventionally believed that diverticula do not cause symptoms.
"The mechanism for the formation of diverticula is unknown. The most widely accepted hypothesis, which we dispute, is that a high-fiber diet bulks the stools, increases colon diameter, and decreases intraluminal pressures ..."
"According to this hypothesis, high pressure and colonic segmentation cause the mucosa to herniate through weak areas in the wall to cause diverticula. However, the high-pressure/pulsion hypothesis would not explain right-sided diverticula ... where the bowel diameter is large and increased muscular contraction is not seen."

The study was supported by the National Institutes of Health.
The authors had no relevant disclosures.

Primary source: Gastroenterology
Source reference:
Peery AF, et al "A high-fiber diet does not protect against asymptomatic diverticulosis" Gastroenterology 2012; DOI: 10.1053/j.gastro.2011.10.035.