The analysis included 11 diets that lasted 3 to 12 weeks. The participants had been diagnosed with diarrhea or mixed types of irritable bowel syndrome.

The following diets increased the chances of improving overall IBS scores more than the participants’ usual diets:

Starch- and sucrose-restricted diet by 59%
Gluten-free diet by 55%
Tritordeum-based diet (a Spanish cereal with lower levels of gliadins and fructans) by 52%
Low-FODMAP diet by 49%
Personalized diet (tailored to individual tolerances and preferences, based on food diary records) by 46%
FODMAP-simple diet (eliminates fructans and galacto-oligosaccharides only) by 44%
Low-carbohydrate diet by 43%
British Dietetic Association diet (regular small meals and limited alcohol, caffeine, carbonated drinks, and fatty foods) by 38%

The risk of bias was unclear in most of the trials.

Which diets are more likely to improve irritable bowel syndrome? Original paper