Effect modification of body mass index and body fat percentage on fatty liver disease in a Japanese population.

BACKGROUND AND AIM: No previous study has performed multivariate analysis of the risk factors of fatty liver disease (FL), focusing on the effect of weight gain of ≥ 10 kg since the age of 20, and no analysis model exists that simultaneously evaluates body mass index (BMI) and body fat percentage (BFP) as adjustment variables. METHODS: To investigate these, we collected anthropometric data from health checkups, and conducted a cross-sectional study (targeting 1851 males and 1259 females aged 30 years or over). RESULTS: Regardless of sex, weight gain of ≥10 kg since the age of 20 was positively associated with FL. Our stratified analysis of BFP into two categories, to evaluate the interaction between BMI and BFP in FL, indicated an approximately fivefold increase in the odds ratio in the male group with high BMI and BFP values compared to those with low BMI and BFP values, with a synergy index of 1.77 > 1. On the other hand, females demonstrated no significant additive interaction, with a synergy index of 0.49 < 1. CONCLUSIONS: We revealed that weight gain ≥ 10 kg since the age of 20 is significantly associated with FL regardless of sex. In addition, by performing a synergy index (S), we showed that the additive interaction between BMI and BFP in FL differs according to gender.