Nonlinear association between body fat percent and type 2 diabetes risk in Japanese adults: a retrospective cohort study.

BACKGROUND: Type 2 diabetes (T2D) has emerged as a major global public health challenge, with dyslipidemia playing a pivotal role in its pathogenesis. Body fat percentage (BFP), a direct measure of adiposity, surpasses body mass index (BMI) in identifying metabolic risk; however, its prospective association with incident T2D remains unclear. OBJECTIVE: To systematically investigate the association between BFP and the risk of incident T2D and to identify potential nonlinear thresholds. METHODS: A large-scale retrospective cohort study was conducted involving 15,464 Japanese adults with a mean follow-up of 6.05 years. Cox proportional hazards regression models were employed to estimate hazard ratios (HRs), and restricted cubic spline analyses were performed to assess nonlinear relationships. RESULTS: BFP was identified as an independent risk factor for T2D. After comprehensive adjustment for confounders, each 1% increase in BFP corresponded to a 6% increase in T2D risk (HR = 1.06, 95% CI: 1.04-1.09). Crucially, restricted cubic spline analysis revealed a significant nonlinear "hockey-stick" pattern, identifying an inflection point at 21.65%. Below this threshold, the risk rose sharply with increasing BFP (HR = 1.18, 95% CI: 1.03-1.36); above it, the upward trend plateaued. This association remained robust in subgroups with normal waist circumference and absence of fatty liver disease, underscoring BFP's unique utility in detecting normal-weight obesity. CONCLUSION: BFP serves as a crucial predictor of T2D. Maintaining BFP below 21.65% may represent a novel target for personalized diabetes prevention strategies.