Prebiotic Fibre
Food for beneficial gut bacteria: supports microbiome diversity and digestive health.
What is Prebiotic Fibre?
Prebiotics are non-digestible fibres that serve as food for beneficial gut bacteria. Unlike probiotics (which are the bacteria themselves), prebiotics are the substrate that helps existing beneficial bacteria thrive and multiply. Inulin and FOS are the most studied types, found naturally in chicory root, garlic, onions, leeks, and artichokes.
What does the evidence say?
A 2017 meta-analysis by Koh et al. in Cell confirmed that prebiotic fibre significantly increases Bifidobacterium and Lactobacillus populations. A 2015 Cochrane review found prebiotics reduce incidence of necrotising enterocolitis and all-cause mortality in preterm infants, the strongest evidence base. In healthy adults, human studies show consistent improvements in stool consistency, reduced constipation, and modest improvements in glycaemic control.
Good evidence from several studies, but with some limitations in size, duration, or methodology.
Dosage guide
| Effective dose | 5–15g per day |
| Maximum dose | 30g/day (above which bloating becomes significant for most people) |
| Timing | Spread through the day: avoid large single doses which cause more gas. |
Best form to buy
Inulin or FOS from chicory root. Psyllium husk is a well-studied prebiotic fibre alternative with good evidence for cholesterol and blood glucose management.
Who benefits most
Men eating a low-fibre diet (which is most men in the UK), those taking probiotics (prebiotics enhance their effectiveness), and anyone wanting to improve digestive regularity.
Side effects and safety
Bloating and gas are common when first starting: start with 3–5g and increase gradually. Well tolerated long-term once the gut adjusts.
“Start by eating more garlic, onions, and leeks. If that's not happening consistently, a chicory inulin supplement is cheap and effective. This is a better long-term investment for gut health than most probiotic supplements.”