What is rumination syndrome? It’s a functional gastrointestinal disorder that occurs when food that is swallowed – but not yet digested – gets regurgitated and comes back up from the stomach, through the esophagus and into the mouth. Children with rumination syndrome will either have to re-chew and re-swallow the undigested food or spit it out. Rumination syndrome, sometimes called rumination disorder, is a reflex, not a purposeful behavior and stems from errors in the way the brain and digestive system interact.