Six-week-old male Fischer 344 rats were randomly allocated into 6 groups (n = 36/group) to receive either AIN-93G (control) or diets containing fructooligosaccharides,
wheat bran (WB), oat bran (OB),
polydextrose, or high-
amylose maize
starch (HAMS), each adjusted to contain a total DF concentration of 7% (wt:wt) and have a fermentability of 3% (wt:wt). After 2 wk, 24 rats/group received 2 subcutaneous doses of
azoxymethane (at 15 mg/kg
body weight) 1 wk apart while 12 rats/group were injected with a saline vehicle; all rats were maintained on the assigned diets for 24 wk postinjection and then killed. Colon
tumor outcomes and pathology together with cecal
short-chain fatty acid composition were assessed.
RESULTS: No
tumors were found in saline-injected rats, and all subsequent analyses were restricted to
azoxymethane-injected rats. Colon
tumor incidence was significantly lower in the
polydextrose (21%) and WB (13%) groups than in the control group (63%; P < 0.05) but not different from the
fructooligosaccharide (58%), HAMS (46%), and OB (33%) groups. In comparison to the control group (8 proximal/31 total
tumors), fermentable materials reduced the number of
tumors (P < 0.05) originating in the proximal colon: HAMS (5/15),
polydextrose (2/7), OB (2/9), fructooligosaccharides (1/21), and WB (1/3). The mean ± SEM number of
tumors/
tumor-bearing rats was significantly lower in the WB (1.00 ± 0.00), OB (1.13 ± 0.13), and HAMS (1.36 ± 0.15) groups than in the control group (2.07 ± 0.27; P < 0.02); other groups did not differ. The mean ± SEM
tumor burden/diet group was lower in the WB (1.2 ± 0.7 mm2),
polydextrose (6.7 ± 3.2 mm2), and OB (7.0 ± 3.0 mm2) groups than in the control (21.4 ± 5.9 mm2) and
fructooligosaccharide (22.1 ± 7.1 mm2; P < 0.05) groups but not significantly different from the HAMS group (15.1 ± 6.1 mm2). Total cecal SCFA concentrations did not differ among diet groups (overall mean ± SEM: 81 ± 4 μmol/g wet weight).
CONCLUSION: