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Sun, Jun 16, 2019

The Health Benefits of Fruits and Vegetables

The following was prepared by Mary Ann S. Van Duyn, Ph.D., M.P.H., R.D. and appeared in Year 2000 Dietary Guidelines – The Case for Fruits and Vegetables First, A Scientific Overview for the Health Professional, Produce for Better Health Foundation, 1999.


Diverticulosis was tagged the “byproduct of our refined eating habits” in a recent Mayo Clinic Health Letter (100). It is found predominantly in industrialized nations and is one of our most common medical conditions. An estimated one-third of people at age 50 have diverticulosis, and this increases to two-thirds of those over 80 years (101). Thus, diverticulosis is clearly linked with aging and its prevalence had been increasing among Western populations over the years.

“…Diverticulosis was tagged the ‘by product of our refined eating habits' in a recent Mayo Clinic Health Letter…An estimated one-third of people at age 50 have diverticulosis, and this increases to two-thirds for those over the age of 80 years…High fiber diets…are now known to provide the best defense against the development of diverticulosis.”

Diverticulosis occurs when small, out-pouches called diverticulum develop in the large intestine or colon. In most cases, this condition is asymptomatic; only an estimated 10-25% of affected individuals become symptomatic (102). Symptoms develop when the colonic diverticulum and surrounding tissues become inflamed, frequently as the result of obstruction by dietary products or stool. This inflammation of the diverticulum is called diverticulitis. Afflicted individuals experience abdominal pain, fever, and tenderness upon examination, and, if left untreated, diverticulitis can result in perforation, or tearing, and inflammation of the abdominal wall.

High fiber diets, which help to increase stool bulk and moisture, and reduce travel time through the gastrointestinal tract, are now known to provide the best defense against the development of diverticulosis. This role for diet in the prevention of diverticulosis came first from the epidemiological data. People in less industrialized countries with higher fiber diets were observed to be at much lower risk for diverticulosis than people from industrialized nations, with diets rich in milled flour, refined sugar, and meat (103). Subsequently, data from numerous animal and clinical studies have confirmed and strengthened the science base supporting a protective role for high fiber diets in diverticulosis development (104, 105).

Insoluble fiber may be the type of dietary fiber most responsible for this protective role. Recent prospective work by Aldoori and colleagues found that insoluble fiber, and particularly cellulose, was significantly associated with decreased risk for diverticulosis among a large group of male health professionals (n=43,881 men) (106). Earlier work by these same researchers identified an association between the fiber from fruits and vegetables, not cereal sources, and reduced risk of diverticulosis (107).

Fruits and vegetables are known generally to be higher in cellulose, one type of insoluble fiber, than cereals (108). Aldoori and colleagues thought that the higher cellulose in fruits and vegetables, compared with cereals, may explain the association between the fiber from fruits and vegetables, and lower risk of diverticulosis (107). This latest work suggests it is the insoluble fiber that is providing the protective benefit in diverticulosis and particularly the cellulose component in the insoluble fiber.

Work by Marlett conveniently identifies amounts of insoluble fiber in our diets, including that from fruits and vegetables (108). Cellulose accounted for 30% of the insoluble fiber in fruits and 50% or more in vegetables. Most foods contain about a third or less (30% or less) of the total fiber from cellulose, with the exception of legumes which is about half.

Taken together, these results highlight an opportunity to more widely promote the fact that fruits and vegetables provide dietary fiber; and that the insoluble fiber, and especially the cellulose, in fruits and vegetables may be particularly important in helping prevent diverticulosis.


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