Individuals who regularly consume diets high in vegetables and fruit generally have a lower overall risk for cancer. Bioactive food components (BAFC) found in fruits and vegetables have been investigated for anti-cancer effects. Animal and cell culture research suggests that these components have relevant biological activity, and as such, diets rich in these components hold significant potential to reduce cancer risk. BAFC are widely distributed in fruits and vegetables and many demonstrate multiple mechanisms of action. These include, but not limited to, direct antioxidative, antiangiogenic and anti-inflammatory effects, as well as modulation of hormone regulation (e.g., aromastase inhibition), detoxification of carcinogens, and key tumor signaling pathways, such as tyrosine kinase inhibition, and promotion of cell cycle arrest. While our understanding of these compounds as potential preventive agents for cancer is substantial, current limitations in the study design impairs progress. Specifically, there is a lack of analytical data of BAFC content in foods, inaccurate dietary exposure estimates, insufficient estimates of biologically effective dose, a lack of biomarkers of intake/exposure to BAFC, and frequent recruitment of "healthy" volunteers rather than individuals with advanced risk for cancer. Understanding these limitations will help to improve study design, as well as fill gaps in our current understanding that in turn will result in clearer, evidencebased, prevention recommendations for BAFC in the human diet.