faecal pH

The pH of the faeces is normally neutral or slightly alkaline (6.8 - 7.5). More acidic stools, physiological only in the newborn, may indicate intestinal infections (Escherichia coli, Rotavirus) or digestive disorders, such as lactose or fat intolerance (steatorrhea from pancreatic insufficiency or biliary stasis).

The pH of the faeces is influenced by the dietary habits of the subject; for example, excessively rich diets of meats and dairy products make the stool more alkaline. The putrefactive intestinal bacterial flora, in fact, demolishes the amino acids that have escaped absorption, generating toxic and malodorous amines; consequently, the pH of the faeces tends to increase as a result of the increased production of ammonia. It is therefore no coincidence that a too alkaline fecal pH, accompanied by a reduction of short chain fatty acids (see butyrate), has been related to an increased risk of colorectal cancer.

If the pH of the faeces tends to increase in the presence of putrefactive dysbiosis, it tends to go down in the presence of fermentative dysbiosis, whose causes of origin are to be found in the excessive ingestion of carbohydrates or a bad absorption of the same (celiac disease) . Even in the presence of abundant lipid intake, in vegetarian diets and prolonged fasting, the pH of the faeces becomes acid.

To avoid distorting the results of the examination, the faeces must not be contaminated with urine and must be rapidly refrigerated to prevent urinary ammonia and putrefactive bacteria from making the fecal pH alkaline.