The Impact of Nutritional Management on Fat-Soluble Nutrient Status in Patients with Fatty Acid Oxidation Disorders: A Cross-Sectional Study

Background: Fatty acid oxidation disorders (FAOD) are rare inborn errors of metabolism that impair mitochondrial β-oxidation and energy production. Management includes fasting avoidance for all FAOD types. Patients with long-chain FAOD are advised to restrict long-chain triglycerides (LCTs) to 10% of total energy intake and supplement medium-chain triglycerides (MCTs). The impact of such dietary modification on fat-soluble vitamin status has not yet been studied. Methods: In this cross-sectional study, serum concentrations of vitamins A, 25(OH)D, E, and β-carotene were measured in 36 FAOD patients and 36 healthy controls matched for age and sex. Vitamins A, E, and β-carotene were quantified using high-performance liquid chromatography and vitamin 25(OH)D through an immunoassay. FAOD patients were further divided into fat-modified (LCT-restricted) and standard-fat diet subgroups based on dietary management. Results: FAOD patients had significantly higher vitamin A concentrations than controls (p < 0.05), while there was no difference in vitamins 25(OH)D, E, and β-carotene. Within the FAOD cohort, the fat-modified group had higher levels of vitamins A and 25(OH)D but lower levels of vitamin E and β-carotene than the standard-fat group (all p < 0.05). Vitamin 25(OH)D deficiency (