Probiotics: Strain-Specific, or Nothing

Probiotics are the supplement category where the gap between the marketing and the evidence is widest — not because nothing works, but because what works is far more specific than what is sold.

Genus, species, strain

A label reading Lactobacillus rhamnosus gives you a genus and a species. The trials were run on Lactobacillus rhamnosus GG — the GG is the strain, and it is the part that carries the evidence. A different rhamnosus strain is a different organism with different behaviour, in roughly the way two breeds of dog are.

A product that does not print the strain designation is telling you it has no specific evidence behind it.

Where the evidence is actually decent

• Antibiotic-associated diarrhoea — Saccharomyces boulardii and L. rhamnosus GG, both reasonably well supported
• Acute infectious diarrhoea, particularly in children — shortened duration, consistently shown
• Irritable bowel symptoms — some multi-strain formulations show benefit, though results vary widely between individuals
• Vaginal and urinary tract health, with specific lactobacillus strains

Where it thins out

General wellbeing, immunity, mood, weight, skin. The mechanisms proposed are plausible and the early research is interesting, but the trial results do not currently support taking a daily capsule for these reasons.

Feeding what is already there

The bacteria you swallow mostly pass through. The ones already resident are the ones that respond to what you feed them — which is why fibre and fermented food do more than a capsule for most people.

• Fermented food supplies live organisms and the compounds fermentation produces: sauerkraut, kefir, natto, live yoghurt, kimchi
• Prebiotic fibre feeds resident populations. On a low-carbohydrate diet this comes from above-ground vegetables, olives, avocado and nuts rather than grains
• Removing what damages the community — repeated antibiotics, emulsifiers, artificial sweeteners, chronic alcohol — usually matters more than adding anything

If you take one

Pick a product for a named strain with evidence for your specific reason, take it for a defined period rather than indefinitely, and stop if nothing changes. Refrigerated or verified shelf-stable, and taken away from hot drinks.