Kyoto, Japan—A pilot study has found that soluble guar fiber may improve both constipation and irritability in children with autism spectrum disorder (ASD), according to a press release.

The study was published in the Journal of Clinical Biochemical Nutrition.Researchers at the Kyoto Prefectural University of Medicine gave 13 children with ASD 6 grams per day of Sunfiber guar fiber, a product from Taiyo International, as a supplement to their regular diets. By the end of the first week, the release says, all children went from defecating once or twice a week to two to four times a week, and their irritability improved significantly.

Autistic people often have chronic digestive issues, according to the press release, including constipation and leaky gut, thanks to an imbalance in the gut microbiome. And given that the gut microbiome is responsible for creating most of the body’s dopamine, serotonin, and other neurotransmitters, a fiber that supports gut health can also support mental health and happiness—which gets a boost anyway when pain brought about by constipation is reduced.

Derek Timm, Ph.D., RDN, said in the release, “These researchers found that a modest dose of Sunfiber produced results on four levels: tangible (less constipation); prebiotic (modulation of the gut microbiome); biomarker (fewer inflammatory cytokines); and behavioral (less irritability).”