Diets high in fiber won't protect against diverticulosis

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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Bogardus ST. What do we know about diverticular disease? A brief overview. Journal of Clinical Gastroenterology. 2006;40:S108–S111.

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.