Do probiotic pills actually help your gut?

Probiotics can favourably influence the balance of gut bacteria by lowering intestinal pH, displacing harmful bacteria and helping to regulate the immune system. Multiple studies show that this does indeed work, but the effect depends strongly on the specific bacterial strain, the dose and the health problem for which they are used. A probiotic that works for one complaint does not automatically help with another.

The strongest evidence exists for two specific applications: the treatment of acute diarrhoea (particularly caused by rotavirus) and pouchitis, an inflammation that can occur after a particular type of bowel surgery. In children, the European Society for Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) has also issued well-supported recommendations for the use of specific strains in acute gastroenteritis, antibiotic-associated diarrhoea and functional abdominal pain complaints, including infantile colic. To be clear: those recommendations apply only to the strains for which evidence exists, not to 'probiotics' as a category.

For other common complaints the picture is considerably less clear. In irritable bowel syndrome, ulcerative colitis and Crohn's disease, the research findings are contradictory or insufficient to draw firm conclusions. Probiotics cannot at this point be considered a general solution for these conditions.

A practical but crucial point: the brand or product you buy must contain the correct strain and at a sufficiently high dose, generally billions of live bacteria per dose. The health benefits demonstrated for one strain do not automatically apply to another product, even if the label mentions the same genus name (such as Lactobacillus).

For healthy people probiotics are generally safe; the most commonly reported side effects are bloating and flatulence. One important exception: in seriously ill people, people with a severely weakened immune system or people with a central venous catheter, probiotics can in rare cases cause a serious bloodstream infection. Medical supervision is required in those cases. Anyone combining probiotics with antibiotics would do well to take the two at least two hours apart, otherwise the antibiotics may simply kill the probiotic bacteria. Finally, there is promising but still early animal-stage research into a technically modified probiotic (Lactobacillus casei with selenium particles) that reduced intestinal inflammation in ulcerative colitis in mice and monkeys, but this has not yet been tested in humans and is therefore still far from clinical practice.