There is strong evidence that human diverticular disease as being due to fiber deficiency. - GreenMedInfo Summary

The relationship between consumption of dietary fiber (DF) from white bread, wholemeal bread, or bran and the development of diverticular disease of the colon has been investigated in a lifespan study using 1800 Wistar rats in nine diet groups. Use of the rat as a model for the human condition was validated by demonstration of significant relationships between fiber intake and fecal output and transit time, and the observation of true acquired diverticula, both single and multiple. Significant inverse relationships (mostly with p less than 0.001) were observed between the incidence of diverticula (and prediverticula) and the concentrations of fiber in the diets, measured by the neutral detergent fiber and Southgate methods. The study offers strong support to the Painter-Burkitt view of human diverticular disease as being due to fiber deficiency, if the extrapolation from rat to man is valid. On the same assumption, the amount of additional fiber required to be consumed in order to achieve a substantial reduction in incidence of the disease is very large. Effects of fiber on body weight, food intake, mineral levels, blood composition and properties, mortality, organ weights, and incidence of tumors and lesions are reported. Significantly fewer mammary tumors were found in rats fed the very high fiber stock diet than in those fed the purified diets.