The idea that a SIBO test should be several hours long and that distal overgrowth is important is not supported by the scientific literature. The optimal testing is 1 hour. Small intestinal bacterial overgrowth (SIBO) occurs as a result of excessive numbers of bacteria inhabiting the proximal small intestine. Bacterial concentrations greater than 105 organisms per milliliter is diagnostic for SIBO. We know bacteria are colonizing the proximal and not the distal small intestine for several reasons. First, the gold standard method for detection of SIBO is jejunal aspirates. Intestinal fluid of the proximal intestine is sampled, not distal intestinal fluid. Secondly, the consequences of SIBO are the result of competition between bacteria and the human host for ingested nutrients in the intestine. Various functional consequences of bacterial infiltration cause enterocyte damage in the jejunum such as diminished disaccharidase activity, fat malabsorption, decreased amino acid transport and decreased vitamin B12 absorption. Thus, detection of proximal bacterial overgrowth is critical.