Rumination syndrome, or merycism, is a chronic motility disorder characterized by effortless regurgitation of most meals following consumption, due to the involuntary contraction of the muscles around the abdomen.

It is increasingly being diagnosed in a greater number of otherwise healthy adolescents and adults, though there is a lack of awareness of the condition by doctors, patients, and the general public.

These symptoms include the acid-induced erosion of the esophagus and enamel, halitosis, malnutrition, severe weight loss and an unquenchable appetite.

While the number and severity of symptoms vary among individuals, repetitive regurgitation of undigested food (known as rumination) after the start of a meal is always present.

[2] There is seldom nausea preceding the expulsion, and the undigested food lacks the bitter taste and odour of stomach acid and bile.

[2][4] Abdominal pain (38.1%), lack of fecal production or constipation (21.1%), nausea (17.0%), diarrhea (8.2%), bloating (4.1%), and dental decay (3.4%) are also described as common symptoms in day-to-day life.

In infants and the cognitively impaired, the disease has normally been attributed to overstimulation and under-stimulation from parents and caregivers, causing the individual to seek self-gratification and self-stimulus due to the lack or abundance of external stimuli.

The disorder has also commonly been attributed to a bout of illness, a period of stress in the individual's recent past, and to changes in medication.

Trauma-induced individuals describe an emotional or physical injury (such as recent surgery, psychological distress, concussions, deaths in the family, etc.

[2] The most widely documented mechanism is that the ingestion of food causes gastric distention, which is followed by abdominal compression and the simultaneous relaxation of the lower esophageal sphincter (LES).

The swallowing of air immediately prior to regurgitation causes the activation of the belching reflex that triggers the relaxation of the LES.

[3] The primary symptom, the regurgitation of recently ingested food, must be consistent, occurring for at least six weeks of the past twelve months.

Among infants and mentally disabled adults, behavioral and mild aversion training has been shown to cause improvement in most cases.

Placing a sour or bitter taste on the tongue when the individual begins the movements or breathing patterns typical of his or her ruminating behavior is the generally accepted method for aversion training,[15] although some older studies advocate the use of pinching.

[citation needed] In patients of normal intelligence, rumination is not an intentional behavior and is habitually reversed using diaphragmatic breathing to counter the urge to regurgitate.

[14] Alongside reassurance, explanation and habit reversal, patients are shown how to breathe using their diaphragms prior to and during the normal rumination period.

Supportive therapy and diaphragmatic breathing has shown to cause improvement in 56% of cases, and total cessation of symptoms in an additional 30% in one study of 54 adolescent patients who were followed up 10 months after initial treatments.

[14] Individuals who have had bulimia or who intentionally induced vomiting in the past have a reduced chance for improvement due to the reinforced behavior.

[22] First described in ancient times, and mentioned in the writings of Aristotle, rumination syndrome was clinically documented in 1618 by Italian anatomist Fabricus ab Aquapendente, who wrote of the symptoms in a patient of his.

[20][22] Among the earliest cases of rumination was that of a physician in the nineteenth century, Charles-Édouard Brown-Séquard, who acquired the condition as the result of experiments upon himself.

As a way of evaluating and testing the acid response of the stomach to various foods, the doctor would swallow sponges tied to a string, then intentionally regurgitate them to analyze the contents.

[24] While the base of patients to examine has gradually increased as more and more people come forward with their symptoms, awareness of the condition by the medical community and the general public is still limited.