Waist circumference (WC) is linked to non-alcoholic fatty liver disease (NAFLD) incidence. However, the impact of longitudinal WC changes on NAFLD remains unclear. We investigated WC trajectories and NAFLD incidence in a large population-based cohort.

We analyzed data from 2666 participants without NAFLD, who underwent biennial check-ups for 16 years, divided into a 6-year exposure period and a 10-year event accrual period. Participants were classified into increasing and decreasing WC trajectory groups during the median 5.9-year exposure period by group-based trajectory modeling. Multiple Cox proportional hazard regression analysis estimated the hazard ratio (HR) and 95 % confidence interval (CI) for incident NAFLD.

During the median 9.7-year event accrual period, 799 participants developed NAFLD. The increasing WC trajectory group had a higher NAFLD risk than the decreasing group, with an HR of 1.20 (95 % CI: 1.02–1.42). After adjusting for confounders, the adjusted-HR was 1.28 (95 % CI: 1.07–1.53). Subgroup analyses revealed significant findings for groups, regardless of abdominal obesity status.

An increasing WC trend was associated with a higher NAFLD risk, independent of abdominal obesity status. Monitoring WC changes may facilitate early detection of NAFLD risk groups and promote lifestyle modifications to prevent NAFLD onset.