Do probiotic pills actually help your gut?

Probiotics can improve the balance of gut bacteria by lowering intestinal pH, crowding out harmful bacteria, and helping to regulate your immune system. But the effect depends strongly on the specific bacterial strain, the dose, and your particular complaint. A probiotic that works for one problem does not automatically help with another.

The strongest evidence exists for two applications: acute diarrhoea caused by the rotavirus and pouchitis, an inflammation that can occur after a specific type of bowel surgery. In children, the European Society for Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) has issued recommendations for specific strains in the context of gastrointestinal infections, antibiotic-associated diarrhoea, and functional abdominal pain such as infantile colic. Note: those recommendations apply only to the strains for which evidence exists, not to 'probiotics' as a category as a whole.

For irritable bowel syndrome, ulcerative colitis, and Crohn's disease, the results are contradictory or insufficient. A general solution for these conditions is not on the horizon for the time being.

Practical but crucial: the product you buy must contain the correct strain and a high enough dose, generally billions of live bacteria per dose. Evidence for one strain does not automatically apply to another product, even if the same genus name such as Lactobacillus appears on the label. For healthy people, probiotics are safe; the most commonly reported side effects are bloating and flatulence. In seriously ill people, people with a weakened immune system, or those with a central venous catheter, probiotics can in rare cases cause a serious bloodstream infection. If you combine them with antibiotics, take both at least two hours apart, otherwise the antibiotics will simply kill the probiotic bacteria.