Ethnic difference in liver fat content: A cross-sectional observation among Japanese American in Hawaii, Japanese in Japan, and non-Hispanic whites in United States

Background: We recently reported that Japanese had higher liver fat at a lower level of BMI compared with non-Hispanic whites (NHW). Objective: We hypothesize that ethnic difference in fat storage capacity contributes to this ethnic difference in liver fat. Design: To examine this, we assessed liver fat among 244 Japanese-American aged 40-49, using regional computed-tomography images, along with metabolic variables. Results: Despite the similar BMI between Japanese-Americans and NHW men, Japanese-Americans had more liver fat (liver to spleen attenuation ratio: 1.03 ± 0.22 for Japanese-Americans, and 1.07 ± 0.15 for NHW men; p < 0.05) and tended to have a greater disposition for fatty liver with an increase in BMI than NHW, indicating a clear difference between the two groups. In addition, liver fat is less in Japanese-Americans compared with Japanese men (1.03 ± 0.22 vs. 1.01 ± 0.16; p < 0.05), despite of a much higher BMI. These ethnic differences support the hypothesis that higher fat storage capacity indeed seems to be associated with less liver fat. In all the groups, liver fat content strongly correlated with triglycerides, homeostasis model assessment-insulin resistance, and C-reactive protein (CRP). Nevertheless, these metabolic variables were worse in Japanese-Americans, despite of less liver fat, compared with Japanese. Moreover, CRP levels were least among Japanese with highest liver fat, and highest among NHW men with least liver fat, despite of a strong positive association between CRP and fatty liver within each population. Conclusions: Fat content in the liver is intermediate for Japanese-Americans compared with Japanese and NHW men, which supports the hypothesis of less fat storage capacity among Japanese, closely linked to ethnic difference in predisposition to fatty liver.