Personalized Optimal Fat Intake for Glycemic Health: Evidence of a U‐Shaped Association and Heterogeneity From NHANES

BACKGROUND: The optimal dietary fat intake for glycemic control is debated. We investigated the dose-response relationship between the fat energy ratio and HbA1c, determined an optimal level, and assessed effect modification by age and diabetes status. METHODS: This cross-sectional study included 6639 U.S. adults from NHANES 2017-2020. The fat energy ratio was derived from two 24-h dietary recalls. Associations with HbA1c were assessed using restricted cubic splines and multivariable regression, adjusting for sociodemographic, lifestyle, clinical, and dietary covariates. RESULTS: A significant nonlinear, U-shaped association was identified (P - nonlinearity < 0.01). The optimal fat intake for minimal HbA1c was 36.0% (95% CI: 32.1-38.2). Stratified analyses revealed effect modification: the optimal ratio was higher in middle-aged (45-64 years: 36.9%) versus younger (18-44 years: 32.2%) and older adults (≥ 65 years: 32.7%), and in individuals with diabetes (38.0%) who exhibited a pronounced U-shaped curve, unlike the flat association seen in those without diabetes. CONCLUSION: Glycemic control exhibits a U-shaped relationship with dietary fat, with an overall optimum at 36.0% of energy. The ideal intake is context-dependent, being higher in middle-aged and diabetic populations, supporting personalized dietary guidelines over universal fat intake targets.