pH, Stool

Stool pH is dependent in part on fermentation of sugars. Colonic fermentation of normal amounts of carbohydrate sugars and production of fatty acids accounts for the normally slightly acidic pH. If disaccharide intolerance is suspect, simple tests may be performed. Slightly alkaline pH may occur in cases of secretory diarrhea without food intake, colitis, villous adenoma, and possibly with antibiotic usage (with resultant impaired colonic fermentation). A stool pH of <6 (measured by pH paper) is suggestive evidence of sugar malabsorption. Children and some adults notice that their stools have a sickly sweet smell as the result of volatile fatty acids and the presence of undigested lactose. Low stool pH also contributes to the excoriation of perianal skin which frequently accompanies the diarrhea.¹

High fecal pH may be a risk factor for colorectal cancer.^2-6 Intake of oat bran (75−100 g/day over a 14-day period) has been shown capable of reducing fecal pH by 0.4 units.² There is evidence, however, that high fecal pH may be secondarily rather than primarily related to cancer risk.³