For more than 40 years, scientists and physicians have thought eating a high-fiber diet lowered a person’s risk of diverticulosis, a disease of the large intestine in which pouches develop in the colon wall. A new study of more than 2,000 people reveals the opposite may be true.
The study, conducted by researchers at the University of North Carolina at Chapel Hill School of Medicine , found that consuming a diet high in fiber raised, rather than lowered, the risk of developing diverticulosis. The findings also counter the commonly-held belief that constipation increases a person’s risk of the disease.
“Despite the significant morbidity and mortality of symptomatic diverticulosis, it looks like we may have been wrong, for decades, about why diverticula actually form,” said Anne Peery, MD, a fellow in the gastroenterology and hepatology division at UNC and the study’s lead researcher. The study appears in the February 2012 issue of the journal Gastroenterology.
“While it is too early to tell patients what to do differently, these results are exciting for researchers,” said Peery. “Figuring out that we don’t know something gives us the opportunity to look at disease processes in new ways.”
Diverticulosis affects about one-third of adults over age 60 in the United States. Although most cases are asymptomatic, when complications develop they can be severe, resulting in infections, bleeding, intestinal perforations and even death. Health care associated with such complications costs an estimated $2.5 billion per year.
What are diverticulosis and diverticulitis?
Many people have small pouches in the lining of the colon, or large intestine, that bulge outward through weak spots. Each pouch is called a diverticulum. Multiple pouches are called diverticula. The condition of having diverticula is called diverticulosis. About 10 percent of Americans older than 40 have diverticulosis. The condition becomes more common as people age. About half of all people older than 60 have diverticulosis.
Diverticula are most common in the lower portion of the large intestine, called the sigmoid colon. When the pouches become inflamed, the condition is called diverticulitis. Ten to 25 percent of people with diverticulosis get diverticulitis. Diverticulosis and diverticulitis together are called diverticular disease.
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Since the late 1960s, doctors have recommended a high-fiber diet to regulate bowel movements and reduce the risk of diverticulosis. This recommendation is based on the idea that a low fiber diet will cause constipation and in turn generate diverticula as a result of increased pressure in the colon. However, few studies have been conducted to back up that assumption. “Our findings dispute commonly-held beliefs because asymptomatic diverticulosis has never been rigorously studied,” said Peery.
The UNC study is based on data from 2,104 patients aged 30-80 years who underwent outpatient colonoscopy at UNC Hospitals from 1998-2010. Participants were interviewed about their diet, bowel movements and level of physical activity.
“We were surprised to find that a low-fiber diet was not associated with a higher prevalence of asymptomatic diverticulosis,” said Peery. In fact, the study found those with the lowest fiber intake were 30 percent less likely to develop diverticula than those with the highest fiber intake.
What causes diverticulosis?
Because diverticulosis is uncommon in regions of the world where diets are high in fiber and rich in grains, fruits and vegetables, most doctors believe this condition is due in part to a diet low in fiber. A low-fiber diet leads to constipation, which increases pressure within the digestive tract with straining during bowel movements. The combination of pressure and straining over many years likely leads to diverticulosis.
What are the symptoms of diverticulosis?
Most people who have diverticulosis are unaware that they have the condition because it usually does not cause symptoms. It is possible that some people with diverticulosis experience bloating, abdominal cramps, or constipation due to difficulty in stool passage through the affected region of the colon.
How is the diagnosis of diverticulosis made?
Because most people do not have symptoms, diverticulosis is often found incidentally during evaluation for another condition or during a screening exam for polyps. Gastroenterologists can directly visualize the diverticula (more than one pouch, or diverticulum) in the colon during a procedure that uses a small camera attached to a lighted, flexible tube inserted through the rectum. One of these procedures is a sigmoidoscopy, which uses a short tube to examine only the rectum and lower part of the colon. A colonoscopy uses a longer tube to examine the entire colon. Diverticulosis can also be seen by other imaging tests, for example, computed tomography (CT) scan or barium x-rays.
The study also found constipation was not a risk factor and that having more frequent bowel movements actually increased a person’s risk. Compared to those with fewer than seven bowel movements per week, individuals with more than 15 bowel movements per week were 70 percent more likely to develop diverticulosis.
The study found no association between diverticulosis and physical inactivity, intake of fat, or intake of red meat. The disease’s causes remain unknown, but the researchers believe gut flora may play a role.
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.
Peery said more research is needed before doctors change dietary recommendations, but the study offers valuable insights on diverticulosis risk factors. “At this time, we cannot predict who will develop a complication, but if we can better understand why asymptomatic diverticula form we can potentially reduce the population at risk for symptomatic disease,” said Peery.
UNC co-authors include Patrick Barrett, Doyun Park (currently at Albert Einstein College of Medicine), Albert Rogers, Joseph Galanko, Christopher Martin and Robert Sandler, gastroenterology & hepatology division chair. The research was supported by grants from the National Institutes of Health.
University of North Carolina School of Medicine