Onion intake might reduce the risk of
colorectal cancer, according to epidemiology. However, Femia showed in 2003 that diets with a 20% onion intake increase
carcinogenesis in rats. We speculated this dose was too high. Prevention of initiation was thus tested in 60 rats given a 5% dried onion diet or AIN76 diet, and initiated 12 days later with
azoxymethane (AOM, 1x20 mg/kg i.
p.), 2-amino-3-methylimidazo[4,5-f]
quinoline (IQ, 2x200 mg/kg p.o.), or N-nitroso-N-
methylurea (2x50 mg/kg p.o.). Prevention of promotion was tested in 38 rats given AOM, then randomised to: AIN76 diet; 5% onion diet;
phytochemicals diet (supplemented with propyl-
disulfide, quercetine-
glycosides and
oligofructose); 1%
pluronic F68 diet (a potent chemopreventive PEG-like block-
polymer, used as a positive control).
Aberrant crypt foci (ACF) were scored 30 days (initiation) or 100 days (promotion) after
carcinogen injection. The onion diet given during initiation reduced the number of AOM-induced ACF (60 versus 86, p=0.03), and the size of IQ-induced ACF (1.33 versus 1.97, p=0.02). Given post-initiation, the onion diet reduced the number of ACF (34 versus 59, p=0.008) and of large ACF (6 versus 15, p=0.02).
Phytochemicals diet and
pluronic diet reduced ACF growth similarly. Data show that a 5% onion diet reduced
carcinogenesis during initiation and promotion stages, and suggest this
chemoprevention is due to known
phytochemicals.