Dried Blood Spot Whole-Blood Fatty-Acid Profiles and Maximum Carotid Wall Thickness in Chinese Adults with Carotid Structural Involvement: A Dual-Route Compositional Cross-Sectional Study

Background/Objectives: Questionnaires regarding intake and routine lipid panels do not indicate fatty-acid composition. Dried blood spot (DBS) whole-blood profiling is a minimally invasive complement not yet linked to a vascular structural endpoint. We tested whether DBS composition tracks carotid wall burden in Chinese adults with metabolic-risk features and established carotid structural involvement using a prespecified panel and compositional analysis. Methods: Fasting DBS gas chromatography resolved 37 fatty acids in 230 adults (47.4% men) meeting a prespecified maximum carotid wall thickness (max-CWT) ≥ 1.0 mm eligibility criterion. A total of 16 prespecified measures were modelled against ln(max-CWT) with multivariable adjustment and Benjamini–Hochberg correction pooled across 16 tests; the 26-part composition was examined by isometric log-ratio (ILR) analysis. Results: Under pooled false-discovery-rate control, α-linolenic acid (ALA) and linoleic acid (LA) were inversely and oleic acid positively associated with max-CWT (per 1-SD β = −0.063, −0.068 and 0.080; all q < 0.05). The full composition was associated (F(25,196) = 2.26, p = 0.0011), whereas EPA and the AA/EPA ratio remained weaker, family-level signals. Conclusions: To our knowledge, this is the first dual-route DBS compositional analysis linked to a structural vascular endpoint, and it identified a candidate nutritional–metabolic pattern—lower ALA and LA and higher oleic acid—linked to wall thickness in adults with established structural involvement. This pattern warrants prospective investigation and does not by itself support any dietary recommendation.