Most diseases, their occurrence and progression, are affected by genetic and environmental factors. In searching for genetic influences in disease it is important to investigate different races or groups living in similar environments. On the other hand, it is important also to simplify the many environmental factors when seeking environmental effects on the onset or progression of diseases in groups having similar genetic background. These two strategies of investigation, varying genetic constitution within similar environments and varying environments but constant genetic constitution, are complementary.

In ischemic heart disease (IHD), several factors such as hypertension (Kannel et al., 1971a; WHO, 1982), hyperlipoproteinaemia (Keys et al., 1958; Kinch et al., 1963; Kannel et al., 1971b), diabetes mellitus (Donahue et al., 1987; Fuller et al., 1980), obesity (Gordon & Kagan, 1981), and smoking habit (Mimura et al., 1984) are thought to be related to its progression. These risk factors are influenced, at least in part, by environmental factors. Out of these environmental factors, dietary habit is suggested by many epidemiological studies to be one of the most important. Furthermore, dietary habit varies with the climate, geographical location, socioeconomic situation, and culture and history of the population.

This study compared the structure and background risk factors of IHD together with the nutritional situation in Okinawans and in migrants from Okinawa who were living in Honolulu without intermarriage (Okinawan-American). The leading causes of death are different, IHD and malignant neoplasia in Okinawan-American and Okinawan, respectively, in spite of their having the same genetic ancestry and living in climates of similar temperature (except in the winter season).