Dietary bioactive food components that interact with the immune response have considerable potential to reduce the risk of cancer. Reduction of chronic inflammation or its downstream consequences may represent a key mechanism that can be reduced through targeting signal transduction or through antioxidant effects. Major classes of macronutrients provide numerous examples, including amino acids such as glutamine or arginine, lipids such as the omega-3 polyunsaturated fatty acids, DHA or EPA, or novel carbohydrates such as various sources of beta-glucans. Vitamins such as C and E are commonly used as antioxidants, while zinc and selenium are minerals with a wide spectrum of impacts on the immune system. Some of the most potent immunomodulators are phytochemicals such as the polyphenols, EGCG or curcumin, or isothiocyanates such as PEITC. There is accumulating evidence for cancer prevention by probiotics and prebiotics, and these may also affect the immune response. Genomic approaches are becoming increasingly important in characterising potential mechanisms of cancer prevention, optimising the rational selection of dietary bioactive food components, or identifying humans with differing nutrient requirements for cancer protection.