High Fiber Diets Don’t Prevent Diverticulosis

Back in the 1960s two researchers theorized that a diet low in fiber meant higher pressure inside the colon, leading to the outpouchings of the wall of the colon that we call diverticula. When these diverticula become inflamed, this is called diverticulitis, and symptoms of diverticulitis can range from mild to severe stomach pain (with or without bloating), diarrhea or constipation, nausea and vomiting, and even rectal bleeding. The vast majority of people, however, have what is known as asymptomatic diverticulosis - meaning that they have diverticula but have no symptoms.

For the last forty years we doctors have been telling people to eat a high fiber diet in order to avoid diverticulosis. Unfortunately, it appears that may be poor advice. In a study recently published in the journal Gastroenterology (doi:10.1053/j.gastro.2011.10.035), researchers from the North Carolina School of Medicine and the Albert Einstein College of Medicine sought to identify the relationship between the presence of diverticula and a person's diet.

They recruited over 2000 people between the ages of 30 and 80 who had recently undergone a colonoscopy. This meant that they knew whether or not that person had any diverticula - and in some cases knew how many had been found in their colon. A few days after the colonoscopy the patients were contacted and interviewed regarding their usual diet with a fairly detailed food questionnaire. They also answered questions regarding their physical activity levels, whether they smoked, how often they had a bowel movement, and basic demographic information.

The researchers were then able to compare the diets and habits of those who had diverticula with the diets of those who did not. What they found is contrary to what was previously believed: those who had the most fiber in their diet were 30% more likely to have diverticula than those with the lowest amount of fiber in their diet. It was previously believed that a diet high in fat or red meat, those who were sedentary and those with constipation were more likely to develop diverticula: the researchers found no association between any of these factors and the risk of diverticulosis.

Previous studies that sought to establish a cause or causes of diverticulosis appear to have been flawed, some deeply. The two researchers who formulated the low-fiber-diet theory were comparing the Western diet with the diet of those from Africa, where diverticulitis is less prevalent. They essentially assumed that the African diet was higher in fiber than the Western diet. Another study used people as controls who may have had diverticulosis themselves; they assumed that those without symptoms had no diverticula. Other studies have been flawed in other ways.

What this means for you

This means that we have very little idea what does cause diverticula to form. We do know that people are more likely to develop them as they get older. That said, this is no reason to reduce the amount of fiber in your diet: it's still great for you, helping you reduce your cholesterol, avoid some cancers, and for diabetics, helping you control your blood sugars. Here's more on fiber's benefits, as well as ways you can get more in your diet.

First posted: February 1, 2012