A low FODMAP diet is associated with changes in the microbiota and reduction in breath hydrogen but not colonic volume in healthy subjects

Single-centre, double-blind, parallel-group, randomized controlled trial in healthy adults without known gastrointestinal disorders or prior FODMAP restriction. A total of 37 participants completed the study: 18 in the maltodextrin group and 19 in the oligofructose group.

Participants followed a 7-day low FODMAP diet and received 14 g/day of added carbohydrate, given as 7 g twice daily. The active regimens were oligofructose 14 g/day versus maltodextrin 14 g/day, dispensed in identical opaque containers for blinding.

The short-term low FODMAP diet did not reduce colonic volume; it increased fasting total colonic volume in both groups. In the maltodextrin group, total colonic volume increased by 90 mL (95% CI 6 to 175; P = 0.04) and breath hydrogen decreased by 11 ppm (95% CI 3 to 18; P = 0.006). In the oligofructose group, total colonic volume increased by 110 mL (95% CI 30 to 190; P = 0.01) and breath hydrogen increased by 16 ppm (95% CI -2 to 35), with a between-group breath hydrogen difference of 27 ppm (95% CI 7 to 50; P < 0.01). Both groups showed reduced total microbial load, but oligofructose reversed several of the low FODMAP-associated microbiota shifts. The authors concluded that the mechanisms of symptom relief from low FODMAP diets are unlikely to be explained by reduced colonic distension alone, and that diet-microbiota interactions are complex.

The intervention was brief (7 days), and the sample was small. Participants were healthy adults rather than patients with IBS, so generalizability to symptom outcomes is limited. Microbiota analyses were exploratory and involved multiple comparisons, increasing the risk of chance findings, and no clinical symptom endpoint was assessed.