Background: Long COVID (LC) has been associated with persistent endothelial dysfunction and vascular impairment. Although nutrition is a key modifiable determinant of cardiovascular health, the relationship between dietary macronutrient intake and vascular alterations in LC remains poorly understood. Objective: To evaluate the association between dietary macronutrient intake and markers of vascular structure, arterial stiffness, and vascular aging in patients with LC, including potential sex differences. Methods: We conducted a cross-sectional study including 304 patients with LC. Dietary intake was assessed using a validated 7-day dietary record (EVIDENT study). Vascular evaluation included carotid intima-media thickness (cIMT), carotid-femoral pulse wave velocity (cfPWV), brachial-ankle pulse wave velocity (baPWV), cardio-ankle vascular index (CAVI), augmentation index adjusted to a heart rate of 75 beats per minute (AIx@75), and vascular aging index (VAI), measured using carotid ultrasound and validated devices (SphygmoCor® and VaSera®). Results: The mean age was 53 ± 12, higher in men (p = 0.001). The study included 207 women (68%) and 97 men (32%). Energy intake and carbohydrate intake in g/day showed a negative association with cfPWV in Model 2 (energy intake: β = -0.06; 95% CI: -0.11 to -0.01; p = 0.02; carbohydrate intake: β = -0.47; 95% CI: -0.87 to -0.07; p = 0.02). The percentage of carbohydrate/total energy intake was positively associated with AIx@75 in Model 2 (β = 0.8; 95% CI 0.12 to 1.49; p = 0.02), and percentage of fat/total energy intake showed a consistent inverse association (β = -0.30; 95% CI: -0.49 to -0.11; p = 0.002). No significant associations were observed for cIMT, baPWV, CAVI or VAI. Conclusions: In patients with LC, total energy intake and absolute carbohydrate intake were negatively associated with cfPWV, whereas the relative contribution of carbohydrates and fats to total energy intake showed divergent associations with AIx@75. These findings suggest that both absolute macronutrient intake and relative macronutrient distribution may be related to central arterial stiffness and wave reflection parameters LC. However, given the cross-sectional design of the study, these results should be interpreted as exploratory and do not allow causal inference. Further longitudinal and interventional studies are needed to confirm these findings and to assess whether nutritional strategies may contribute to modulating vascular risk in this population.
