This chapter reviews the numerous nutrients and food components that have been linked to sex steroids, including dietary fiber, fat, carbohydrate, protein, micronutrients, alcohol, and phytochemicals. The chapter also discusses the effects of obesity on sex steroids as well as studies comparing vegetarians with non-vegetarians. Studies comparing vegetarians to non-vegetarians have suggested that low-fat, high-fiber diets are associated with lower serum estrogens, lower urinary estrogens, and higher fecal estrogens. Subsequent studies focusing on the effects of specific nutrients have revealed that metabolism and concentrations of sex steroids can be modulated by changes in amounts of many nutrients, including fiber, fat, carbohydrate and protein, alcohol, and phytochemicals. The significance of these changes has been linked to associations with increased or decreased risk of hormone-dependent diseases, primarily breast cancer, prostate cancer, and cardiovascular disease. It has also been consistently shown that obesity and body fatness contribute to variation in sex steroids.