Does Fibre-fix provided to people with irritable bowel syndrome who are consuming a low FODMAP diet improve their gut health, gut microbiome, sleep and mental health?

Author Identifier

Ran Yan

Date of Award


Document Type



Edith Cowan University

Degree Name

Doctor of Philosophy


School of Medical and Health Sciences

First Supervisor

Amanda Devine

Second Supervisor

Claus Christophersen

Third Supervisor

Johnny LO

Fourth Supervisor

Ian Dunican

Fifth Supervisor

Evania Marlow

Sixth Supervisor

Lesley Andrew


Irritable Bowel Syndrome (IBS) is the most common functional gastrointestinal disorder, affecting 4% of the global population. Despite its effects in symptom alleviation, a diet low in fermentable oligo, di, monosaccharides, and polyols (FODMAP), has been shown to have negative impacts on gut microbiota. This randomised double-blind placebo-control study aimed to examine whether Fibre-fix, a mix of dietary fibres, added to an existing low FODMAP diet, can improve gut health, gut microbiota, sleep, mental health and quality of life in IBS patients without causing exacerbation of symptoms. Adult participants (n=26, 3 males) who had been on a low FODMAP diet for a minimum of one month were recruited from Perth, Western Australia. They were randomised into either the Fibre-fix (n=13) or placebo (n=13) group for a 3-week consumption of the corresponding supplement with doses increased from 5 g/d to 40 g/d, after completing a one-week baseline. At baseline (Timepoint 1, T1) and the end of the study (T2), their blood and faecal samples and 3-day weighed-food diaries were collected. Questionnaires were also collected to evaluate sleep, mental health, quality of life and gut symptoms. During the four weeks, participants also reported their daily IBS symptoms, and wore a wrist-based actigraphy, Readiband®, to capture daily sleep data.

At baseline, the gut microbial composition did not significantly differ between groups. However, at T2, the overall gut composition changed at both the genus (P = 0.0023) and amplicon sequence variant (ASV) level (P = 0.0018), due to the fibre supplement. Fibre-fix beneficially altered gut microbial composition by significantly changing the relative abundance of 10 genera and 35 ASVs at T2, including Ruminococcus E with a 5.5-fold change (fc) (P < 0.01) and Prevotella (fc = 5.9, P > 0.05). At the end of the intervention, no significant changes were noted between groups in gut diversity indices and faecal SCFA. Throughout the interventional period, participants in both groups maintained their baseline sleep patterns and stable symptom severity. Fibre-fix improved GI-specific anxiety (P = 0.010) and sexual subscale of quality of life (P = 0.01). Both groups boosted their fibre intake, achieving the Australian Dietary Guideline (ADG) recommendations (female level) at T2, with overall dietary patterns and quality maintained. Participants in the Fibre-fix group reported less energy and protein consumption than their baseline levels. At T2, a total of 26 variables explained approximately 80% of the gut microbial variation in the taxonomic levels of phylum, genus and ASV, where 6 of the 26 contributed to all three levels, relating to: participants’ compliance (%), fruit intake (serve/day), faecal butyrate concentration, number of bowel movements, sleep quality and daytime sleepiness. This study shows that a correct mix of fibres can alleviate the negative effects of a low FODMAP diet on gut health, improve gut microbiota, reduce GIspecific anxiety, and not impact the sleep and symptoms of IBS patients on this diet compared with those supplemented with the placebo.


Seventh Supervisor: Kanita Kunaratnam



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