Children with autism are four times more likely than other kids to experience gastrointestinal troubles, researchers say in a new study providing the largest look ever at the issue.

Digestive problems like constipation and diarrhea are three times more common and complaints of abdominal pain occur twice as often in those with the developmental disorder, researchers say.

The findings reported online this week in the journal Pediatrics are based on a comprehensive review of medical research on the topic published in peer-reviewed scientific journals between 1980 and 2012.

“Our findings corroborate a history of anecdotal reports and case studies suggesting increased risk of GI concerns in autism,” said William Sharp of the Marcus Autism Center and Emory University School of Medicine who co-authored the study.

It’s unclear what’s leading to a greater prevalence of gastrointestinal problems in children with autism and it’s tough to spot the issues given that such children often have difficulty communicating and may turn to behaviors like self-injury, aggression and irritability when experiencing digestive difficulties, the researchers said.

“Relying on these atypical signs to detect possible GI concerns can be difficult for practitioners because repetitive and stereotyped patterns of behavior occur so frequently in ASD and no guidelines exist to help parents and clinicians navigate the diagnostic process,” said Barbara McElhanon, a pediatric gastroenterologist at Children’s Healthcare of Atlanta and an assistant professor of pediatrics at Emory University School of Medicine who worked on the review.

Accordingly, the researchers said their findings point to a need for standardized screening methods and clinical guidelines to be established to help health care providers spot gastrointestinal issues in kids with autism.