Dietary fiber is a crucial component of a healthy diet, with benefits that can be attributed to processes in the gut microbiota and the resulting by-products. Observational studies support associations between dietary fiber intake and depression and inflammation, but the potential mechanisms are poorly understood. This review examines evidence of the effects of dietary fiber on depression and inflammation and considers plausible mechanisms linking dietary fiber and depression, including microbiota-driven modification of gene expression and increased production of neurotransmitters. Additionally, inflammation may mediate the relationship between dietary fiber intake and depression. A high-fiber diet potentially lowers inflammation by modifying both the pH and the permeability of the gut. The resultant reduction in inflammatory compounds may alter neurotransmitter concentrations to reduce symptoms of depression. Further research into the link between dietary fiber intake and inflammation and depression is essential, as findings could potentially provide guidance for improvement in or prevention of inflammatory and depressive disorders.

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A high dietary fibre intake has been associated with improvements in inflammatory conditions in adults. However, little is known on whether associations between dietary fibre and inflammation are evident during adolescence. We examined the relationship between dietary fibre intake measured by food frequency questionnaire and the inflammatory marker high-sensitivity C-reactive protein (hs-CRP) and the adipokines leptin and adiponectin cross-sectionally in 17-year-olds participating in the Raine Study (n=621). In weighted analysis using tobit and linear regression, and after excluding participants with hs-CRP>10mg/L, higher total dietary fibre intake (per 5g/day) was significantly associated with lower leptin (β=-0.13, 95% CI -0.17, -0.09) and adiponectin (β=-0.28, 95% CI -0.49, -0.07), but not hs-CRP, in unadjusted analyses. These associations were no longer significant after adjustment for gender, anthropometry and a number of lifestyle factors. However, higher cereal and grain fibre intake was significantly associated with lower leptin (β=-0.06, 95% CI -0.10, -0.01) in fully adjusted analysis. Our findings suggest that a higher intake of cereal and grain fibre may contribute to lower leptin in adolescents. This may contribute to reductions in low-grade chronic inflammation and improved health outcomes.