Stomach Bugs / Gastroenteritis

A promising finding that didn't hold up

Acute gastroenteritis, a stomach bug causing vomiting and diarrhoea, is most often caused by viruses like rotavirus or norovirus. For years, the leading evidence on probiotics came from a 2010 Cochrane review of 63 trials. It suggested probiotics shortened diarrhoea by about 25 hours and cut the risk of it dragging on for four or more days by 59%. That review has since been updated. The 2020 update added newer, larger, more rigorous trials, including two large well-conducted studies, bringing the total to 82 trials and over 12,000 participants. Using stricter methods to account for publication bias, the update reversed the earlier conclusion. Restricted to the studies at the lowest risk of bias, it found no meaningful difference between probiotics and placebo in how long diarrhoea lasted.

Source: Probiotics for treating acute infectious diarrhoea

Source: Do probiotics help to treat acute infectious diarrhoea?

The infection itself still reshapes the gut

Even though probiotics as a treatment didn't hold up under stricter scrutiny, the infection's effect on gut bacteria is well documented. A study comparing 39 children with rotavirus infection to 8 healthy children found the infected children's gut bacteria shifted significantly, with more of certain bacteria groups linked to inflammation. The same research team found that children who had received two doses of the rotavirus vaccine had a distinctly different, and more diverse, gut bacteria pattern than unvaccinated children or those with only one dose, hinting that gut bacteria may help explain why the vaccine works better in some children than others.

Source: Gut Pathogens, Microbiome profiling of rotavirus infected children suffering from acute gastroenteritis

Why the picture is so mixed

The heterogeneity between trials is a large part of why the overall conclusion flipped. Some trials of specific strains, including Lactobacillus rhamnosus GG, found real reductions in symptom duration in earlier, smaller studies, while later large, well-conducted trials found no protective effect for that same strain. Researchers who ran the 2020 update pointed to publication bias, meaning smaller studies showing a benefit were more likely to get published than smaller studies showing none, as one likely reason the earlier, more optimistic picture didn't survive contact with bigger, better trials.

Source: The Complex Interactions Between Rotavirus and the Gut Microbiota

What this means for you

Most stomach bugs resolve on their own with rest and fluids, but signs of dehydration, blood in stool, high fever, or symptoms lasting more than a few days need medical attention, especially in young children and older adults. Given how the evidence has shifted, a specific probiotic strain shouldn't be relied on to shorten a stomach bug. Fluids and electrolyte replacement remain the proven core of home management. A varied, plant-rich diet, resumed as soon as it's tolerated, still supports the gut bacteria this research shows get disrupted by the infection itself. That's the same idea behind GutLab, everyday gut health starts with regularly feeding the microbiome a broad range of plant-rich ingredients.