Abstract
ABSTRACTDietary fibre is an umbrella term comprising various types of carbohydrate polymers that cannot be digested nor absorbed by the human small intestine. Consumption of dietary fibre is linked to beneficial effects on cognitive and affective processes, although not all fibres produce the same effects. Fibres that increase short-chain fatty acid (SCFA) production following modulation of the gut microbiota are thought to be the most potent fibres to induce effects on cognitive and affective processes. SCFAs can exert their effects by improving central, peripheral and systemic immunity, lowering hypertension and enhancing intestinal barrier integrity. Here, we propose additional mechanisms by which dietary fibres may contribute to improvements in affective and cognitive processes. Fibre-induced modulation of the gut microbiota may influence affective processes and cognition by increasing brain-derived neurotrophic factor levels. Depending on the physicochemical properties of dietary fibre, additional effects on affect and cognition may occur via non-microbiota-related routes, such as enhancement of the immune system and lowering cholesterol levels and subsequently lowering blood pressure. Mechanistic randomised placebo-controlled trials are needed to establish the effects of dietary fibre consumption and the magnitude of explained variance in affect and cognition when incorporating measurements of microbiota-dependent and microbiota-independent mechanisms in humans.
Highlights
Dietary fibre, which is derived from fruits and vegetables, legumes, whole-grain breads and cereals, is an umbrella term comprising various types of carbohydrate polymers that cannot be digested nor absorbed by the human small intestine
Dietary fibre consumption can aid in prevention or treatment of symptoms of depression, anxiety, and stress (Jacka et al, 2017; Silk et al, 2009), which are psychological states characterised by negative mood that are often accompanied by impaired facets of cognition
We shed light on additional potential mechanisms that may contribute to the positive effects of dietary fibres on these processes, such as the immune system, cholesterol, the intestinal barrier, brain-derived neurotrophic factor (BDNF), and blood pressure, and would help explain additional variance that is not explained by short chain fatty acids (SCFAs)
Summary
Dietary fibre, which is derived from fruits and vegetables, legumes, whole-grain breads and cereals, is an umbrella term comprising various types of carbohydrate polymers that cannot be digested nor absorbed by the human small intestine. Since dietary fibres vary in origin, chemical composition, and physicochemical properties (comprising solubility, fermentability, and viscosity), they can exert different effects on the body. These differences in physicochemical properties might differentially affect the communicative pathways to the brain, and variably influence affective and cognitive processes. Since in human studies most studies are associative, we included animal studies that assess the impact of dietary fibre intake on these various mechanisms To this end, the current review assesses microbiota-dependent and microbiota-independent biological mechanisms that may underlie the effects of dietary fibre on affective processes and cognition and outlines which physicochemical properties may predict such effects
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