Dietary Fibres on Gut Fermentation

Overview

The goal of this clinical trial is to learn if adding a rapidly fermenting fibre to a meal containing a slow fermenting fibre affects gut bacterial fermentation and digestive comfort in healthy adults aged 18 to 85 years. The main questions it aims to answer are: * Does the addition of a fast fermenting fibre to a meal containing a slow fermenting fibre change the timing and amount of gas produced by gut bacterial fermentation? * Does the addition of a fast fermenting fibre as a split dose effectively reduce the digestive discomfort typically caused by consuming a high dose of fibre all at once? Researchers will compare the effect of adding fructo-oligosaccharides (FOS) over-and-above a single dietary fibre (soluble corn fibre). They will also compare whether taking FOS either all at once versus splitting it into two smaller doses affects gut bacterial fermentation and digestive comfort. Participants will: * Visit the research laboratory for 3 test days, with a 1-week break between visits. * Avoid certain foods and fast overnight before each test day. * Eat a test breakfast and lunch containing the dietary fibres in different parts of the meal. * Provide breath samples every 30 minutes to measure gas produced by gut bacteria. * Answer survey questions about their digestive comfort every 30 minutes. * Keep a diary of their bowel movements for 5 days during each test cycle. Short-chain fatty acids (SCFAs) produced through dietary fibre fermentation are essential for maintaining intestinal barrier integrity and regulating systemic metabolism; however, average daily fibre intake frequently remains below recommended levels. While supplementing with highly fermentable fibres, such as fructo-oligosaccharides (FOS), effectively stimulates beneficial microbial activity in the proximal colon, their rapid breakdown often triggers acute gastrointestinal discomfort, including bloating and flatulence. Conversely, soluble corn fibre (SCF) possesses a highly branched structure that ferments slowly and reaches the distal colon, exhibiting excellent gastrointestinal tolerability but yielding a lower initial peak of SCFA production.

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.