Association between dietary fibre intake and depressive symptoms before and during the COVID-19 pandemic

BACKGROUND: Emerging evidence indicates that dietary fibre may influence mental health via mechanisms related to the gut-brain axis. However, population-level evidence examining the association between dietary fibre intake and depressive symptoms before and during the COVID-19 pandemic remains limited. We examined the associations between energy-adjusted and energy-unadjusted dietary fibre intake and depressive symptoms across these two time periods. METHODS: We analysed data from the National Health and Nutrition Examination Survey (NHANES) conducted before the COVID-19 pandemic (January 2017-March 2020; n = 7,513) and during the pandemic (August 2021-August 2023; n = 4,680). Depressive symptoms were assessed using the Patient Health Questionnaire-9 (PHQ-9), with scores ≥10 indicating depression. Dietary fibre intake (g/day) was assessed using a 24-h dietary recall. Energy-adjusted dietary fibre intake was derived using the residual method to account for total energy intake, thereby isolating the effect of fibre independent of total caloric consumption. Associations between energy-adjusted and energy-unadjusted dietary fibre intake and depressive symptoms were estimated using modified Poisson regression models, adjusting for relevant covariates including sociodemographic characteristics. RESULTS: The prevalence of depression increased from 8.0% pre-pandemic to 10.1% during the pandemic. Mean dietary fibre intake decreased from 16.52 g/day pre-pandemic to 15.95 g/day during the pandemic. Each additional 5 g of energy-adjusted fibre intake was associated with a 14% lower prevalence of depressive symptoms before the pandemic (adjusted prevalence ratio (aPR) = 0.86; 95% CI: 0.81, 0.92)), whereas the association was attenuated during the pandemic (aPR = 0.98; 95% CI: 0.91, 1.05). In energy-unadjusted analyses, a 1 g/day increase in fibre intake was associated with a 2% lower depression prevalence (aPR = 0.98; 95% CI: 0.97, 0.99) pre-pandemic but was insignificant (aPR = 0.99; 95% CI: 0.98, 1.00) during the pandemic. Gender-stratified analyses revealed that prior to the pandemic, higher energy-adjusted dietary fibre intake was associated with a lower prevalence of depressive symptoms among men (aPR = 0.79; 95% CI: 0.71, 0.88) and women (aPR = 0.91; 95% CI: 0.84, 0.99). During the pandemic, the association was attenuated among men (aPR = 1.04; 95% CI: 0.92, 1.17), whereas a modest protective association persisted among women (aPR = 0.90; 95% CI: 0.81, 0.99). CONCLUSIONS: Higher energy-adjusted dietary fibre intake was associated with lower depressive symptoms before the pandemic in both men and women. During the pandemic, however, the protective association persisted only among women. These findings suggest that dietary fibre may offer continued mental health benefits for women even under societal stressors, highlighting its potential as a gender-specific nutritional target for depression prevention.