Fiber: Friend or Foe?
A recent study by researchers at the University of North Carolina (UNC) made headlines after being published in the February issue of Gastroenterology. The study consisted of data collected on the reported activity level and diet of 2,104 patients (30 to 80 years old) who had undergone an outpatient colonoscopy between 1998 and 2010. They reported no significant association between activity level or the intake of meat or fat and the presence of diverticulosis. However, they did find that those who reported the lowest fiber intake were actually 30% less likely to have had diverticulosis than those who reported consuming more fiber. In marked contrast to the UNC, Dr. Crowe reported on a large study last summer. He followed 47,033 men and women living in England or Scotland for several years. About one-third of the subjects in Dr. Crowe’s study reported consuming a vegetarian diet. He found that people with a higher fiber diet (> 25g/day) had a significantly lower risk of being admitted to a hospital with or dying from diverticular disease than those eating a diet with more meat and less fiber. Indeed, among the vegans in this study the reduction in hospitalization for symptomatic diverticular disease was reduced 72% (1). How do we make sense of such apparently contradictory findings?
A Brief History
Clinical observations made by two missionary doctors in rural Africa back in the 1960s and 1970s indicated that bowel diseases common in England and the US were virtually absent among rural Africans whose diets were high in fiber and very low in fatty animal products. In 20 years of practice in rural Africa, these doctors saw almost no cases of diverticulosis, hemorrhoids, inflammatory bowel disease, or type 2 diabetes. They suggested diverticular disease did not occur in rural Africans largely because their mostly vegetarian diet was much higher in fiber than that consumed in modern Western countries (2). Indeed, studies of human populations around the world have consistently shown that wherever a high-fiber, largely vegetarian diet gets displaced by a diet much higher in meat and refined carbohydrates, the prevalence of diverticulosis and diverticulitis and many other abdominal ills increases markedly. Research in animals has shown that a low fiber intake promotes diverticulosis. Indeed, clinical studies have shown that treating people with symptomatic bowel disease generally relieves most of their symptoms (3).
Given the overwhelming data indicating bowel problems and numerous other ills result in large part from a typical Western diet, the recent (apparently contradictory) data from the UNC study should not alter clinical practice. Indeed, given the clinical improvement often seen with increased fiber intake in those with bowel disease, it may well be the correlation between higher fiber and more diverticulosis is an example of reverse causation. Simply put, those with symptoms of diverticular disease may well have been more likely to have increased their fiber intake to help reduce their symptoms. So, for now, we're sticking with the data from all those other studies. Fiber is your friend.
By James J. Kenney, PhD, FACN
1. BMJ 2011; DOI: 10.1136/bmj.d4115
2. Br Med J. 1979 Jun 30;1(6180):1795
3. Postgrad Med J 1974;50:629-35
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