Estimated Body Fat Percentage and Triglyceride-Glucose Index for Identifying MASLD in Lean Asian Adults: A...

Metabolic dysfunction-associated steatotic liver disease (MASLD) is increasingly prevalent among lean Asian populations, yet effective strategies for identifying high-risk individuals remain limited. We investigated the associations of body fat percentage (BF%) and the triglyceride-glucose (TyG) index with lean MASLD and evaluated their incremental diagnostic value in two independent studies (the NAGALA cohort and a Chinese health check-up study). Lean MASLD was defined as imaging-confirmed hepatic steatosis in individuals with BMI < 23 kg/m². In both studies, participants with MASLD were older, more often male, and exhibited less favorable metabolic profiles. Multivariable analyses showed that the TyG index was consistently associated with increased odds of lean MASLD (adjusted OR per unit increase: 3.41 in NAGALA and 6.37 in the Chinese study), whereas associations of BF% varied by cohort and sex, with significant associations observed in NAGALA men and Chinese women (adjusted OR per unit increase: 1.20 and 1.24, respectively). In ROC analyses, the TyG index showed good discrimination (C-statistics 0.778-0.875), and the addition of BF% further improved performance (0.805-0.901), corresponding to an absolute increase of approximately 0.02-0.05, with consistent improvements in net reclassification and discrimination (all p < 0.05). Mendelian randomization analyses supported a potential causal association between the TyG index and NAFLD, while no significant causal association was observed for BF%. Overall, BF% and the TyG index provide complementary information, and their combined use improves the identification of lean MASLD.