Probiotics
Live bacteria that modulate the gut microbiome
What is Probiotics?
Probiotics are live microorganisms that, when consumed in adequate amounts, confer a health benefit on the host. The human gut contains approximately 38 trillion bacteria (similar to the number of human cells), collectively called the gut microbiome. The composition of this microbiome profoundly influences digestion, immunity, mental health, inflammation, and metabolic health. Probiotic supplementation temporarily introduces beneficial strains to support and modulate this ecosystem.
How it works
Probiotic bacteria exert effects through multiple mechanisms: competitive exclusion of pathogens (occupying space and binding sites), production of short-chain fatty acids (SCFAs — particularly butyrate, which fuels colonocytes and has anti-inflammatory effects), modulation of the intestinal epithelial barrier (tight junction protein upregulation), direct immune system modulation (via toll-like receptors and regulatory T-cell induction), and synthesis of neurotransmitter precursors (the gut-brain axis).
What the evidence shows
Probiotics have the strongest evidence for: antibiotic-associated diarrhoea prevention (2012 JAMA meta-analysis of 82 RCTs showed significant risk reduction), IBS symptoms (meta-analyses consistently show benefit, with some strains outperforming others), H. pylori eradication (as adjunct), prevention of necrotising enterocolitis in premature infants, and C. difficile infection prevention. The gut-brain axis evidence is emerging — several RCTs show psychobiotic effects on stress, anxiety, and depression scores.
When to expect results
Microbiome begins shifting. Some people experience more gas and bloating as bacteria establish — this is normal.
Digestive symptoms stabilising. Stool consistency and transit improving in those with IBS or irregular bowel.
Noticeable improvement in bloating and gut comfort. Immune function improving (mucosal immunity enhanced).
Sustained microbiome modulation. Stress resilience improving (gut-brain axis). Reduced frequency of infections in some users.
Dosing
Measured in CFU (colony-forming units). Typically 1–50 billion CFU per day. Higher doesn't always mean better — strain identity matters more than CFU count. Most studies use 5–20 billion CFU. Take with or just before food (food provides a buffer that improves bacterial survival through stomach acid). Keep refrigerated unless the product is specifically shelf-stable.
Forms to choose
Strain specificity is crucial — different strains have completely different effects. Lactobacillus acidophilus (gut barrier, IBS), L. rhamnosus GG (antibiotic-associated diarrhoea — most studied probiotic strain), L. reuteri (H. pylori, cholesterol), Bifidobacterium longum (IBS, stress), L. plantarum (IBS, inflammation), B. breve (infant gut health, atopy). Multi-strain products often cover more ground, but ensure each strain has evidence for your goal.
Who benefits most
Anyone who has recently taken antibiotics, people with IBS, IBD in remission, recurring UTIs (certain strains), women with BV or recurrent thrush, people with high stress (psychobiotic effects), anyone with generally poor gut health (bloating, irregular transit), and people eating a low-fibre Western diet.
Who should avoid / caution
Severely immunocompromised individuals (solid organ transplant, chemotherapy) should use only under medical supervision. People with short bowel syndrome or central venous catheters should also discuss with their specialist.
Interactions & stacking
Take probiotics 2+ hours away from antibiotics (not simultaneously — the antibiotic may kill the probiotic). Start probiotics as early as possible during a course.
Prebiotics (inulin, FOS, psyllium, resistant starch) feed probiotic bacteria. Combining pre- and probiotics (synbiotics) is more effective than probiotics alone.
Antifungal medications may also affect some probiotic yeast strains (e.g., Saccharomyces boulardii). Separate in time.
Probiotic effects are significantly enhanced by a high-fibre diet that feeds the introduced bacteria and supports the wider microbiome.
Safety & side effects
Common initial side effects: bloating, wind, altered stool — usually resolve within 1–2 weeks as the microbiome adjusts. Serious adverse events are extremely rare in healthy people. People who are severely immunocompromised should discuss with their doctor — there are theoretical (very rare) risks of bacteraemia.
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This information is for educational purposes only and does not constitute medical advice. Always consult your GP or a qualified healthcare professional before starting any new supplement, particularly if you are pregnant, breastfeeding, have a medical condition, or are taking prescription medication.