Macronutrient Intake and Clinical Manifestations in Adults with Long COVID-19: A Cross-Sectional Analysis of the BioICOPER Study

Background/Objectives: The relationship between macronutrient intake and the clinical manifestations of long COVID-19 remains poorly understood. This study examined these associations in adults from the BioICOPER cohort. Methods: This cross-sectional study included 290 adults with long COVID-19 from the BioICOPER cohort who had complete seven-day dietary records collected using the EVIDENT application. Twelve clinical outcomes were assessed using linear regression with robust standard errors, ordinal logistic regression for frailty, and multinomial logistic regression for dyspnea. Model 1 examined eight exposures (total energy and seven nutrient intake variables), adjusting for age and sex. Model 2 examined seven exposures expressed as energy percentages or fiber density, additionally adjusting for total energy intake. Benjamini–Hochberg correction was applied separately to the 96 and 84 tests, respectively. Results: In Model 1, higher intakes of total fat (odds ratio [OR]: 0.983; 95% confidence interval [CI]: 0.974–0.992), saturated fatty acids (OR: 0.956; 95% CI: 0.932–0.981), and monounsaturated fatty acids (OR: 0.967; 95% CI: 0.948–0.987), per additional g/day, were associated with lower odds of being in a higher frailty category (q: 0.034, 0.034, and 0.038, respectively). No primary association in Model 2 remained significant after correction for multiple testing. Exploratory analyses identified quadratic relationships between the energy percentages from protein and polyunsaturated fatty acids and Montreal Cognitive Assessment (MoCA) scores (q = 0.0163 and 0.0111, respectively). Conclusions: Absolute intakes of certain fats were inversely associated with frailty, whereas the primary analyses of energy-adjusted dietary composition showed no significant associations after correction for multiple testing. These findings do not support recommending a specific macronutrient distribution. The exploratory cognitive findings require replication in longitudinal studies.