Symptoms of small intestinal bacterial overgrowth, according to the SIBO Center for Digestive Health, include:
Bloating
Belching
Cramps
Constipation
Diarrhea
Heartburn (reflux or GERD)
Nausea
Food sensitivities
Headaches
Joint pain
Fatigue
Skin rashes
Respiratory symptoms (such as asthma)
Mood symptoms (such as depression)
Brain symptoms (such as autism)
Eczema
Steatorrhea (fatty stools)
Iron deficiency anemia
Flatulence
Abdominal pain
Vitamin B12 deficiency
Research from the University of Southern California published in the Journal of the American Medical Association indicated that the symptoms of SIBO were nearly universal to those symptoms associated with irritable bowel syndrome.
Source: 21 Symptoms of Small Intestinal Bacterial Overgrowth