Figure 1.

Overview of potential biological mechanisms underlying dietary fibres’ effects on mood and cognition according to physicochemical properties. The degree of viscosity, fermentability, and solubility of dietary fibres influences gut microbiota composition and function, the immune system, as well as cholesterol levels, through which mood and cognition can be modulated. Via the direct immune route, viscous, fermentable, and soluble fibres can reduce pro-inflammatory cytokines, lower numbers and activation of splenic macrophages and DCs, and increase neutrophils in the blood. Cholesterol levels can be lowered by viscous, fermentable, and soluble fibres and impact the brain, but can also indirectly affect it by reducing hypertension. Fermentability and solubility of dietary fibre modulate the gut microbiota, by which it can influence affective and cognitive processes via SCFA-dependent mechanisms or BDNF levels. SCFAs can lower hypertension as well as improve immune function and intestinal barrier integrity. Via the indirect immune route, SCFAs suppress pro-inflammatory reactions by reducing pro-inflammatory cytokines, increasing anti-inflammatory cytokines and T_reg cells, as well as restoring microglial cell morphology and reversing microglial immaturity. All these mechanisms have been associated with modulation of mood and cognition in health and disease. The likelihood that the different biological mechanisms underlie dietary fibres’ effect on mood and cognition are displayed in proportion, with larger cubicle areas reflecting increased potential. The green plus sign indicates beneficial effects. BDNF, brain-derived neurotrophic factor; DCs, dendritic cells; T_reg cells, regulatory T-cells; SCFAs, short chain fatty acids.