Comparisons of diets and disease rates between Adventists and non-Adventists, and prospective cohort studies among Adventists, have contributed greatly to our general understanding of nutrition and health. The most fundamental conclusion drawn from the Adventist Health Studies has been that maintaining a lean body weight throughout life is central for optimal health. Other contributions have included the value of nut consumption for prevention of coronary artery disease, and the roles of red meat and dairy products in the etiologies of cardiovascular disease and cancer. Although much progress has been made, many issues remain unresolved. In particular, rates of breast and prostate cancers remain high among Adventist populations despite an overall healthy lifestyle and long life expectancy. There is even some suggestion that risk of breast cancer may increase with duration of being a vegetarian. One topic that may be uniquely studied among an Adventist population is the effect of soy phytoestrogens in disease prevention. Although soy consumption has been hypothesized to contribute to the low rates of breast cancer in Asian populations, several intervention studies using high doses of soy estrogens have shown changes in breast nipple fluid that would predict higher rates of breast cancer. Also, high dairy product consumption has been associated with risk of prostate and ovarian cancers in some but not all studies. The unusually wide range of milk consumption in Adventists will be particularly informative with regard to these relations. Resolution of these issues is needed to provide optimal guidance regarding healthy diets, and the newly funded Adventist Health Study will contribute importantly in this effort.