FRIDAY, April 12, 2019 (HealthDay News) -- Scientists suspect that your gut microbiome -- the mix of bacteria that inhabit your intestines -- affects your health in many ways, but a surprising new finding suggests that a healthy microbiome may even ease the symptoms of autism.

The small study of 18 children with autism who also had severe digestive problems found that a fecal transplant to rebalance their gut microbiome reduced both their digestive symptoms and their autism symptoms. The improvements persisted during the two-year study follow-up period.

"We treated children with autism by altering the gut microbiota. All had gastrointestinal symptoms -- diarrhea, constipation, stomach pain -- and those symptoms were reduced dramatically, and their behavior improved as well," said study senior author Rosa Krajmalnik-Brown. She's a professor at the Biodesign Institute at Arizona State University in Tempe, Ariz.

"When we checked again two years later, behavior was even better and gastrointestinal symptoms were still much better, but not as good as right after treatment," she said.

Krajmalnik-Brown said it's not clear exactly how improving the microbiome helps autism symptoms. Because all of the children had severe digestive issues, she said it's possible that "they may be more comfortable and better able to focus and learn," she suggested.

It also might be that healthier microorganisms in the gut may send chemicals to the brain that help children learn and make connections, she added.

The researchers noted that 30% to 50% of people with autism also have chronic digestive problems that may make them irritable and make it difficult to learn, pay attention and behave well.

The kids treated in the study were found to have a low diversity of bacteria in their intestines at the beginning of the study. All 18 received the fecal transplant daily for seven to eight weeks.

The treatment increased the diversity of microbes and healthy bacteria in the gut, according to the researchers.

When the study started, 83% of the children were classified as having severe autism. At the end of the study, only 17% were severe, 39% were mild or moderate, and 44% were below the cut-off for mild autism spectrum disorder, the findings showed.