The Role of Dietary Fibres in the Gut-Microbiota-Brain Axis

Liaquat, Marrium (2026) The Role of Dietary Fibres in the Gut-Microbiota-Brain Axis. Doctoral thesis, University of East Anglia.

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Abstract

Dietary Fibre (DF) is increasingly recognised as a key regulator of the gut-microbiota-brain (GMB) axis; however substantial interindividual variability exists in responses to DF interventions. This thesis examined how DF type, biological sex, dietary context, and genetic risk influence gut microbiota composition, metabolic activity, and downstream mental and cognitive health outcomes. Using preclinical models, baseline sex differences in gut microbiota composition, and gut-metabolomic profiles were first characterised, revealing pronounced male-female divergence. Building on this foundation, the effects of isolated DF interventions were investigated using inulin and psyllium, selected for their contrasting fermentability. Inulin induced marked, sex-dependent alterations in gut microbiota composition and metabolic output, whereas psyllium elicited more modest, largely sex-independent effects. A combined DF intervention generated heterogenous responses, highlighting interactive effects between fibre types. Together, these findings demonstrate that DFs are not functionally equivalent and that fermentability and host sex critically influence GMB communication. To translate these mechanistic insights into humans, the impact of DF within whole dietary patterns was assessed. In adults with mild to moderate anxiety and/or depression, short-term adherence to a high-fibre Mediterranean-style diet resulted in rapid shifts in gut microbiota composition and metabolite profiles, which were associated with improvements in mental health outcomes. These results highlight the sensitivity of the GMB axis to high-DF vs low-DF dietary patterns. Finally, habitual DF intake was examined in relation to cognitive performance in older adults with Subjective Cognitive Impairment (SCI) or Mild Cognitive Impairment (MCI), stratified by APOE4 genotype. Higher DF intake was associated with better cognitive performance in non-APOE4 carriers, whereas no clear associations were observed in APOE4 carriers, underscoring the importance of genetic context in shaping dietary responsiveness. Collectively, this thesis advances the understanding of DFs as a biologically active dietary component and supports the development of personalised, DF-based strategies to support mental and cognitive health.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Medicine and Health Sciences > Norwich Medical School
Depositing User:	Chris White
Date Deposited:	30 Mar 2026 10:45
Last Modified:	30 Mar 2026 10:45
URI:	https://ueaeprints.uea.ac.uk/id/eprint/102636
DOI:

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