The prominent features of the chicken diet were high arachidonic acid and niacin. The chicken diet contained 1 g/kg of arachidonic acid [calculated from (31)] compared to 0.25 g/kg in other diets. Arachidonic acid has pro-tumorigenic properties, likely by increasing prostaglandin synthesis (32). In addition, the chicken diet contained 207 mg/kg of niacin, 4 times the 51 mg/kg found in the control diet and twice the value in beef diet (assays done byLARA Lab). Niacin can afford protection against carcinogenesis when added to a niacin-deficient diet (33), but high doses are toxic. Here, the high dose provided by the chicken-based diet would translate to 12 times the recommended daily allowance in humans. High niacin stimulates histamine releaseand prostaglandin synthesis, which might explain the ACF promotion (34). The intake of white meat is not associated with colorectal cancer risk in most epidemiological studies (1,2). In contrast, dietary heme iron intake is associated with an increased risk of proximal colon cancer (35). However, in a prospective cohort study of 34,198 Californian Adventists, the consumption of white meat, mostly chicken, was associated with a tripled risk of colorectal cancer (36). In summary, this study shows for the first time a promoting effect of red meat on carcinogenesis. It corroborates epidemiological observations: high red meat intake is associated with increased colon cancer risk. In previous meat studies (3–13), the promoting effect of meat was inhibited by dietary calcium, as shown by the study of Parnaud et al. (13). Furthermore, MDF promotion was related to heme intake. Promotion was significantly greater for the high-heme black pudding diet than for the medium-heme beef diet. This heme effect is in line with recent epidemiological data (35). The low-heme chicken diet did not promote MDF, but did increase ACF formation. For red meat diets, promotion was associated with high fecal water lipoperoxidation, cytolytic activity, and increase of pH, which may explain the increased carcinogenesis.