Our understanding of the relationship between diet and prostate cancer is still developing. Currently, randomized, controlled trials are under way that will yield evidence on which to base recommendations regarding dietary regimens, functional foods, and supplement use. For now, data mostly derive from epidemiologic investigations with limited ability to demonstrate cause and effect, or from benchtop research that may have limited application to in vivo systems, especially in humans. Insufficient evidence currently exists to support the use of specific dietary supplements or functional food. Clinicians striving for best clinical practice should therefore encourage weight management because data consistently show that overweight and obesity are associated with progressive disease and increased overall mortality from prostate cancer and other diseases, especially cardiovascular disease.