Probiotics: What the Evidence Actually Supports

HEALTH · GLOBAL

Probiotics: What the Evidence Actually Supports

Why strains matter, where benefits are shown, survivability and who should take care

Probiotics are sold as a general good, and the research is far more specific than that. The useful question is which strain, for which problem.

Effects are strain specific

Evidence attaches to particular strains at particular doses rather than to probiotics as a category. Saccharomyces boulardii has reasonable evidence for antibiotic-associated diarrhoea; certain lactobacillus strains have evidence in irritable bowel syndrome.

A product listing only genus and species — lactobacillus acidophilus, say — without the strain designation cannot be matched to any study.

Where benefits are reasonably shown

Reducing antibiotic-associated diarrhoea, some improvement in IBS symptoms for some people, and infant colic with specific strains. Beyond that the evidence thins quickly.

General claims about immunity, mood and energy are far ahead of the research.

Dose and survivability

Check the colony forming units per dose and whether that figure is guaranteed at the end of shelf life rather than at manufacture. Many products state CFU at production, which is a considerably weaker claim.

Storage matters, since some strains need refrigeration.

Give it time, then stop

Four to eight weeks is a reasonable trial. If nothing has changed, the product is not working for you and continuing is spending money.

Who should take advice first

Anyone immunocompromised, seriously ill, with a central line or with a damaged gut barrier, since there are documented cases of infection. Speak to a doctor rather than self-prescribing.

Reading a supplement label

Look for the full strain designation, the guaranteed count at end of shelf life, and any prebiotic content. A proprietary blend without quantities cannot be assessed against any research.

Check for allergens, since some cultures are grown on dairy or soy media.

Alongside antibiotics

Where a probiotic is used for antibiotic-associated diarrhoea, it is generally taken a few hours apart from the antibiotic and continued for a period afterwards. Ask a pharmacist.

Fermented foods

Live yoghurt, kefir, sauerkraut, kimchi and miso contain live cultures and have reasonable supporting evidence. Heat-treated versions sold on a shelf contain none, so check where they are sold.

Introduce them gradually, since a sudden increase commonly causes bloating and wind.

Fibre

Most people eat well below the recommended amount, and increasing it gradually is the single best-supported change for gut health. Thirty different plants a week is a useful target, counting herbs, nuts, seeds and wholegrains.

Cook and cool starchy foods such as potatoes and rice to increase resistant starch, which feeds gut bacteria.

What has stronger evidence

Dietary diversity — a wide range of plants across a week, plenty of fibre and fermented foods — has better support than any capsule, and feeds the bacteria you already have.

Persistent digestive symptoms need a proper diagnosis rather than a supplement bought online.

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