MONDAY, Jan. 23, 2012 (MedPage Today) — 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 percent 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 coauthors 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 percent of the diverticulosis group had three or more diverticula, 40 percent had one or two, and 32 percent 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.
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.
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.
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."
Last Updated: 1/24/2012