The gut microbiome has become one of the most exciting areas in medical research. Probiotics — live microorganisms that confer a health benefit — have been extensively studied, with evidence varying dramatically by strain and condition. Here’s an honest look at what works and what doesn’t.

Not All Probiotics Are the Same

This cannot be overstated: probiotic effects are entirely strain-specific. A randomised trial showing that Lactobacillus rhamnosus GG reduces acute diarrhoea duration by 1 day tells you nothing about whether Lactobacillus acidophilus NCIMB 701748 (a different strain) does the same. Yet most OTC probiotics are sold with generic health claims that lump all strains together. When evaluating probiotic evidence, always ask: which specific strain (species AND strain designation), which dose (in CFUs), for which specific condition?

Where the Evidence Is Strongest

Antibiotic-associated diarrhoea prevention: Saccharomyces boulardii CNCM I-745 and Lactobacillus rhamnosus GG are the two strains with the most consistent, high-quality evidence for reducing AAD risk (by approximately 40%). Start alongside the antibiotic, not after. Acute infectious diarrhoea (in children): L. rhamnosus GG and S. boulardii reduce duration by approximately 24 hours. IBS: Bifidobacterium longum 35624 (Alflorex) has the strongest RCT evidence for IBS overall. L. acidophilus NCFM helps IBS-D. Results take 4–8 weeks. C. difficile infection prevention: high-dose S. boulardii and multi-strain preparations in hospitalised patients on antibiotics have evidence. Vaginal health: oral L. rhamnosus GR-1 and L. reuteri RC-14 have evidence for reducing recurrent BV. Immune function: limited but growing evidence for reducing incidence and duration of common respiratory infections.

Prebiotics: Feeding the Microbiome

Prebiotics are dietary fibres that selectively feed beneficial bacteria. Inulin, fructooligosaccharides (FOS), galactooligosaccharides (GOS) and resistant starch are the most studied. Increasing dietary fibre diversity is the most effective way to improve microbiome diversity. High-polyphenol foods (berries, dark chocolate, green tea, olive oil) also selectively stimulate beneficial bacteria. Fermented foods (kefir, natural yoghurt, kimchi, sauerkraut) provide both live bacteria and prebiotics and have the most convincing real-world evidence for microbiome health.

Browse Digestive Health products at Huncoat Pharmacy. Related: Gut Health Guide, IBS Guide.

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