AbstractDietary intake has been hypothesized as being associated with several hormonally related cancers including prostate, breast, ovarian, and endometrial cancer. Because diet may affect hormones directly, it is logical to examine the effects of dietary factors on hormone production and levels. Therefore, a set of 72 male MZ and 83 male DZ twin pairs was ascertained from the Utah birth certificates. A quantitative food frequency questionnaire was administered and blood samples were drawn for hormonal assays. Heritability estimates for hormonal levels were calculated indicating a range from no heritability for sex hormone binding globulin (SHBG), estrone, and testosterone glucuronide to 70% for androstanediol glucuronide and luteinizing hormone. To examine nutritional factors, the difference in hormone and SHBG levels between each MZ twin and his co‐twin were correlated with the difference in nutrient intake. Weight and obesity were significantly correlated with plasma testosterone and follicle stimulating hormone. Fat intake showed a significant association with testosterone. Androstanediol glucuronide, a steroid that reflects tissue formation of dihydrotestosterone, was inversely correlated with caloric intake, theobromine and caffeine. Testosterone glucuronide exhibited significant correlations with calories and vitamin A. This study suggests that dietary intake affects plasma sex‐steroid levels in