Dietary intake of soy protein decreases tumor incidence in rat models of chemically-induced colon cancer. We hypothesized that decreased expression of Fatty Acid Synthase (FASN) underlies, in part, the tumor preventive effects of soy protein, since FASN over-expression characterizes early tumorigenesis. Here, we show that colonic FASN levels are reduced with dietary intake of Soy Protein Isolate (SPI), compared to control Casein (CAS) diet, in male Sprague-Dawley rats administered the colon carcinogen azoxymethane (AOM). SPI consumption resulted in decreased serum insulin levels and decreased AOM-induced tumor suppressor p53 phosphorylation in colon crypt epithelium. To evaluate potential links between insulin and FASN leading to DNA damage, C2BBe1 colon epithelial cells, treated with insulin and/or the carcinogen NMU were evaluated for DNA damage and apoptosis after transfection with control or FASN siRNAs. While the numbers of DNA apurinic/apyrimidinic (AP) sites (bio-marker of DNA damage) induced by NMU were unaffected by transfection of FASN siRNA, insulin induction of these sites was decreased with FASN knockdown. By contrast, NMU-induced apoptosis of C2BBe1, as well as intestinal epithelial IEC-6 cells, was enhanced by transfected FASN siRNA. Increased Fasn expression in IEC-6 cells by addition of LXR agonist T0901317 did not affect AP site number but enhanced cell killing by cerulenin, a FASN inhibitor. Moreover, insulin rescued NMU-treated cells from apoptosis in an FASN-dependent manner. Results suggest that dietary SPI, by decreasing circulating insulin levels and colon FASN expression, attenuates insulin-induced DNA damage and FASN-mediated anti-apoptosis during carcinogenesis, resulting in an overall reduced tumorigenic state.