Table 1 Inclusion and exclusion criteria for patients in the study and control groups.

Functional constipation diagnosed according to Rome IV criteria

Age > 3 years old

Consent to participate in the study

Patients without constipation, in whom organic diseases have been ruled out, not under the care of specialized clinics

Age > 3 years old

Consent to participate in the study

Probiotics in the previous 4 weeks

Antibiotic therapy within the last 4 weeks

Eating less than 2 h apart when saliva is collected

The presence of genetic syndrome, psychomotor developmental delay, chronic encephalopathy, spina bifida, Hirschsprung's disease, anatomical defects of the lower gastrointestinal tract (including anal stenosis), celiac disease, disease of the inflammatory bowel disease, infectious colitis