Some dietary components that may not be required for human existence may markedly influence the quality of life by modifying physiologic processes. These compounds can influence, in combination or alone, numerous biological functions by serving as antioxidants, immunoregulators, regulators of gene expression, modulators of several cellular processes, including growth and apoptosis. Many diseases are associated with impaired cell proliferation or differentiation and, what is most important, also with deregulations in programmed cell death, which, in the end, can lead to the promotion of the diseases such as cancer. Biologically-active molecules are capable of modifying the biochemical pathways and/or influencing specific proteins regulating apoptosis in gastrointestinal cells, which can be used for both prevention and treatment. Dietary fibres, cruciferous vegetables, flax and curcumin showed positive effect in the protection of colon cancer. Similarly, a strong inverse relationship between stomach as well as colon cancer risk and allium vegetables intake has been proved. Limonoids from citrus fruits are also considered as promising molecules with anticancer activity, such as perrillyl alcohol, which was tested in patients with advanced malignant tumours. Although the relationship between soy intake and cancer risk has not so far been clearly elucidated, it is known that isoflavones from soy may reduce the risk of estrogen-dependent breast cancer. Although functional foods of animal origin are not that well recognized, some of them, however, seem to be worthy of particular interest. Although interactions among nutrients have been inadequately examined, a few examples of negative and positive interactions exist, e.g. some components may provide beneficial effects by influencing the structure and functions of the wall as well as environment of the gastrointestinal tract, including phytohaemagglutinin (PHA) and other components, such as alpha- etoglutaric acid (AKG).