Dietary Fibres on Gut Fermentation

This study aims to investigate the effect of rapidly fermenting FOS over-and-above slowly fermenting SCF and whether this supports a "spatio-temporal fermentation profile" spanning the entire colonic tract. By balancing fermentation speeds, this strategy holds the potential to maximise total colonic fermentation yield whilst mitigating the adverse symptoms typically associated with isolated high-dose FOS intake. Furthermore, the study explores a split-dosing regimen as an additional temporal strategy; dividing the FOS intake may limit the peak rate of gas production, preventing it from exceeding the gut's natural gas clearance mechanisms, while ensuring a sustained delivery of fermentable substrates.

To evaluate these physiological dynamics, healthy adult participants will complete a randomised, double-blind, crossover trial comprising three distinct acute testing days, separated by 7-day washout periods. Under strict dietary standardisation and overnight fasting conditions, participants will consume meals containing specific dietary fibres. The acute physiological responses will be continuously monitored via non-invasive breath hydrogen and methane analysis to objectively map fermentation kinetics, alongside regular self-reported assessments of gastrointestinal tolerability throughout the testing window.

Inclusion criteria

• Healthy males and females, aged between 18 and 85 years at the start of the study.
• Self-reported regular bowel habits, defined as an average frequency of between 3 and 21 bowel movements per week (Mitsuhashi et al., 2018). This weekly average accounts for normal daily fluctuations while ensuring an overall healthy baseline.
• Willing and able to comply with all study protocols, including pre-test dietary restrictions (avoiding highly fermentable foods), a 12-hour overnight fast, and consumption of the prescribed dietary fibre test meals.
• Willing to accurately record gastrointestinal symptoms using the Visual Analogue Scale (VAS) and complete the Bristol Stool Scale (BSS) logs over the specified periods.
• Able to understand the study procedures and provide written informed consent.

Exclusion criteria

• History or current diagnosis of chronic gastrointestinal diseases or conditions (e.g., Irritable Bowel Syndrome [IBS], Inflammatory Bowel Disease [IBD], coeliac disease, chronic constipation, or history of major gastrointestinal surgery).
• Use of systemic antibiotics, prebiotics, probiotics, or medications known to significantly alter gastrointestinal motility within the 3 months prior to the commencement of, or during the study period.
• Known food allergies or severe intolerances to any ingredients present in the test meals (e.g., soluble corn fibre, fructo-oligosaccharides).
• Females who are currently pregnant, planning to become pregnant during the study period, or lactating.
• Currently following a highly restrictive or extreme diet (e.g., strict ketogenic, extreme high-fibre, or medically prescribed diets) that could significantly confound the baseline gut microbiota or fermentation profile.