Dietary fiber and giardiasis: dietary fiber reduces rate of intestinal infection by Giardia lamblia in the gerbil.

Gerbils were maintained on a low-fiber (5%) or a high-fiber (20%) diet in which the major fiber source was cellulose. Animals in the low-fiber diet group were significantly more likely to become infected when inoculated with 100 Giardia lamblia cysts than were animals in the high-fiber group. No differences were detected in gastrointestinal transit, gastric, and small intestinal luminal pH, or in duodenal mucus blanket acidic glycoprotein between animals in the high- and the low-fiber diet groups at the time of cyst inoculation. The fiber content of the diet after cyst inoculation determined the infection rate. These data suggest that the dietary fiber effect occurred during trophozoite colonization of the small intestine. When infected animals on the low-fiber diet were placed on the high-fiber diet for 24 hr, trophozoite clearing occurred in the lower small intestine. In the jejunum, the number of trophozoites attached to the mucosal surface decreased, while the number associated with luminal mucus increased. We conclude that the fiber-induced mucus secretion and the bulk movement of the insoluble fiber reduced the attachment of trophozoites to the intestinal mucosa, which decreased the probability of trophozoites establishing and sustaining colonization of the mucosa.