We examined the influence of extruded chickpeas and wheat relative to
casein and wheat in a
dimethylhydrazine (
DMH)-induced colon
tumor study in male Sprague-Dawley rats. The three diets, based on a modified AIN76 rodent diet with fat present
at 10 g/100 g dry matter (DM), were as follows:
casein with wheat
starch (Cas/S) as control,
casein with wheat (Cas/W) and chickpeas with wheat (CP/W). All diets were fed from 5 wk of age throughout the 28-wk study. At 28 wk, there was a significantly lower incidence of large intestinal
tumors in rats fed Cas/W relative to those fed CP/W ( 11 vs. 56%, chi-square test, P = 0.018). The colonic
tumor burden (
tumors/
tumor-bearing animal) was not different in Cas/W-fed and CP/W-fed rats (1 vs. 1.7), but the
tumor mass index was significantly lower in the former group (0.22 vs. 1.21, P = 0.026). Rats fed the CP/W diet had significantly lower plasma
cholesterol concentration (P < 0.01) than rats fed the other two diets. The cecal contents of rats fed the CP/W diet had significantly greater relative weights (46%, P < 0.05) than those of the Cas/W-fed rats; this was associated with higher concentrations of all
short-chain fatty acids. Fecal analyses showed significantly (P < 0.05) higher concentrations of total fat (54%), total
steroids (83%) and secondary
bile acids (179%) in the CP/W-fed rats relative those fed Cas/W. There were higher concentrations of
nitrogen in the feces of CP/W rats relative to the Cas/W-fed rats (84%, P < 0.05), associated with greater fecal weights (67%, P < 0.05). Although wheat and its fibers have been shown to be protective against
DMH-induced
cancers in rats, this was not the case in this study in which chickpeas (45 g/100 g diet) provided the
protein and were an important source of soluble fiber. Elevated fat, secondary
bile acid concentrations and/or nitrogenous compounds could be responsible for the increased colon
tumorigenesis seen and may reflect a legume effect.