ABSTRACT
Epidemiological observations have shown an inverse relationship between the consumption of plant foods rich in phytonutrients and the incidence of cancer. This chapter reviews both basic and clinical studies on the effects of phytonutrients on cellular function and carcinogenesis. Dietary botanical supplements made from standardized extracts further concentrate specific phytonutrients enabling meaningful clinical research studies by eliminating the natural variation in plants due to variable growing conditions. Bioactive compounds are compounds that occur in nature within the food chain and have the ability to interact with one or more compounds of living tissue while also demonstrating an effect on human health. Phytonutrients are divided into chemical classes including phenolic acids, alkaloids, nitrogen-containing compounds, organosulfur compounds, phytosterols, and carotenoids. Among the polyphenols there are phenolic acids, stilbenes, lignans, coumarins, tannins, and flavonoids. Tannins of note include hydrolysable tannins such as ellagitannins found in pomegranate and walnuts and condensed tannins found in cocoa. Organosulfur compounds include isothiocyanates, indoles, allyl sulfides, and sulforaphane. Phytosterols inhibit cholesterol absorption and include sitosterol, campesterol, and stigmasterol. Stilbenes include resveratrol and pterostilbene. Carotenoids include alpha- and beta-carotene, beta-cryptoxanthin, lutein, zeaxanthin, astaxanthin, and lycopene. Phytonutrient molecules have been shown to modulate intracellular mechanisms relevant to cancer prevention and treatment. Nutrigenomics and nutrigenetics by integrating nutrition, biochemistry, molecular biology, and genomics have the potential to revolutionize nutrition science in this century. It has been estimated that there are more than 10,000 phytonutrients present in foods, but our current knowledge is limited to the functions and potential preventive properties of the categories of phytonutrients reviewed above. There are too few published clinical trials using phytonutrients for cancer prevention and treatment and this is the great research challenge for the future.
