PURPOSE: Inositol hexaphosphate (IP6) is a naturally occurring polyphosphorylated carbohydrate that has been shown to suppress the growth of epithelial cancer. Because IP6 is a dietary phytochemical present in cereals, soy, legumens, and fiber-rich foods, we evaluated the efficacy of IP6 against colon cancer formation. METHODS: HT-29 cells were injected into nude mice. The animals were fed a normal diet (group 1), a low IP6 diet (group 2), and a high IP6 diet (group 3) for 4 wk. Body weight, tumor volume, tumor growth rate, growth inhibition rate, and therapeutic ratio were monitored after injection of HT-29 cells. RESULTS: HT-29-cell human-colon-carcinoma xenograft mice treated with IP6 showed a significant reduction in tumor growth rate, irrespective of the IP6 dose compared to normal diet group. Compared with the control group, group 3 showed a significant reduction (45%) in tumor volume. In the therapeutic ratio gain profiles, IP6 diet groups showed a significant alteration of therapeutic ratio when compared with the normal diet group (0% vs. 11%, P=0.014). In the body weight gain profiles, group 3 showed a significant reduction of body weight compared with the other two groups (20.25 g vs. 21.6 g, 21.7 g, P=0.009). Groups 1 and 2 showed similar changes in body weight. Tumor xenografts from IP6-fed mice showed significantly decreased cancer formation and growth, but increased toxicity was noted for high doses of IP6. CONCLUSION: These results indicate that in the future, IP6 could be an effective chemopreventive or chemotherapeutic agent for use in the treatment of colon cancer.