Among Asians, including Japanese, obesity is related to dyslipidemia and insulin resistance
at a lower level of body mass index (BMI) compared with non-Hispanic whites (NHW).
We hypothesize that this ethnic difference in the relationship between BMI and metabolic
risks is partly associated with the ethnic difference in fat distribution, namely,
liver fat as well as visceral adipose tissue. To compare liver fat content among Japanese
vs NHW men, regional computed tomographic images were taken to measure liver computed
tomographic density in population-based samples of 313 Japanese and 288 NHW men aged
40 to 49 years, along with the assessment of metabolic parameters. Liver fat content
was higher in Japanese than NHW men (liver to spleen attenuation ratio [lower value
means higher liver fat content]: 1.01 +/- 0.16 vs 1.07 +/- 0.15, respectively; P <
.01), despite a lower mean BMI in Japanese men (BMI: 23.6 +/- 2.9 vs 27.8 +/- 4.2
kg/m(2), P < .01). Moreover, Japanese men had a greater disposition for fatty liver
with a small increase in BMI than NHW (P < .01), whereas both groups had a similar
relationship between visceral adipose tissue and BMI. In both groups, liver fat content
correlated with triglycerides, homeostasis model assessment of insulin resistance,
and C-reactive protein. Liver fat content is higher among Japanese than NHW; and this
ethnic difference becomes more robust with a small increase in BMI, suggesting that
fatty liver is a sensitive marker for the failure of the adipose tissue to expand
to accommodate an increased energy influx, and is associated with similar metabolic
risk in Japanese despite lower BMI compared with NHW men.