Children diagnosed with autism could be at a greater risk of debilitating digestive issues, a study suggests.  

A team of researchers from the University of California, Davis, conducted a study involving more than 300 children diagnosed with autism spectrum disorder (ASD) and compared them with a group of over 150 children without the condition.

The study, which tracked the children for nearly ten years and involved parent-completed questionnaires, revealed that children with autism were initially over 50 percent more prone to experiencing gastrointestinal issues such as bloating, constipation, and diarrhea.

By the end of the study period, autistic children were at a four-fold greater risk of gastrointestinal distress than their neurotypical peers. 

Autistic children also had a greater likelihood of all digestive symptoms, with constipation being the most common issue reported. 

These gastrointestinal challenges were found to exacerbate several typical autism-related behaviors, including social difficulties, repetitive actions like stimming, aggressive outbursts, and sleep disturbances.

Past research suggests restrictive diets often seen among autistic children may limit key nutrients like fiber, leading to bloating, constipation and gas.  

The team noted that screening for gastrointestinal issues may help reduce disruptive behaviors in autistic children and help identify the root of behavior problems in children who otherwise have difficulty communicating.  

Researchers at the University of California, Davis, found autistic children are up to four times more likely than their neurotypical peers to report gastrointestinal issues (stock image)

Dr Christine Wu Nordahl, senior study author and principal investigator at the UC Davis MIND Institute, said: ‘This is not about finding a single cause. It’s about recognizing the whole child.

‘Supporting gastrointestinal health is one important step toward improving overall quality of life for children with autism.’ 

The findings come as one in 31 children in the US is diagnosed with autism, a stark increase from about one in 150 in the early 2000s. 

The study, published in August in the journal Autism, looked at 475 children also enrolled in the UC Davis MIND Institute Autism Phenome Project. Of those, 322 (68 percent) were diagnosed with autism, while the remainder were neurotypical. 

The children were evaluated at three points: baseline (two to four years old), two years later (four to six years old) and ‘middle childhood’ (nine to 12 years old).

Caregivers completed questionnaires about their children’s potential gastrointestinal symptoms, including how often they had abdominal pain, gas, diarrhea, bloating, constipation, pain during a bowel movement, vomiting, difficulty swallowing, blood in the stool or blood in the vomit.  

Parents and caregivers ranked the frequency of each symptom from one to five (ranging from ‘never’ to ‘always’). Children with at least one current GI symptom (within the last three months) were labelled as having gastrointestinal symptoms (GIS).

Of the participants formally diagnosed with a digestive condition, gastroesophageal reflux disease (GERD), a condition in which stomach acid backs up into the esophagus, was the most common.

Of the participants with autism, 43 had reported food allergies, which may have contributed to their symptoms. 

The above graph shows the percentage of children with autism spectrum disorder (ASD) and those who are typically developing (TD) reporting digestive issues at different points in the study. Autistic children showed a greater likelihood throughout the study

The researchers found that 61 percent of neurotypical children never reported GIS compared to 34.5 percent of children with ASD, a 55 percent difference. 

After the initial baseline visit, 47 percent of autistic children reported GIS compared to 30 percent of typically developing participants, making children with autism 44 percent more likely to have gastrointestinal issues at this point. 

By the second visit, 40 percent of autistic children had GIS compared to 15 percent of those in the neurotypical group,  a difference of 91 percent. 

And after the third visit, GIS was recorded in 30 percent of children with autism and seven percent of neurotypical children, more than a four-fold difference. 

Each individual gastrointestinal symptom was more common in children with autism than their neurotypical peers.  

Constipation was the most common symptom in the autistic group, with 32 percent of participants reporting it compared to 11 percent of typically developing children. 

In the neurotypical group, the most common symptom was abdominal pain, seen in 12 percent of patients. Among those with autism, abdominal pain was seen in 17 percent. 

Diarrhea was the second most common symptom in each group, accounting for 27 percent of children with autism and 11 percent of typically developing children. 

The above graph shows the predicted probability of children in the ASD and TD groups developing gastrointestinal issues as they age

The researchers found that over time, children with autism were twice as likely as their neurotypical peers to develop gastrointestinal issues. 

They also noted autistic children with more gastrointestinal symptoms were more likely to have more profound autistic behaviors like repetitive behaviors, anxiety, depression, aggression, defiance, social problems and sleep issues. 

The researchers did not explain why gastrointestinal symptoms are more common in autistic children, but it could be because many of them only eat a select few ‘safe’ foods, which generally are fried, low in fiber and highly processed, increasing the risk of bloating, constipation and diarrhea. 

Autistic people also often have imbalances in their gut bacteria, which may increase the chances of digestive issues. 

The researchers wrote: ‘Results support the need for future research to assess the presence of and persistence of GIS in children with autism throughout childhood.’