OSMOTIC CAUSES Osmotic diarrhea occurs when ingested, poorly absorbable, osmotically active solutes draw enough fluid into the lumen to exceed the reabsorptive capacity of the colon. Fecal water output increases in proportion to such a solute load. Osmotic diarrhea characteristically ceases with fasting or with discontinuation of the causative agent. Osmotic Laxatives Ingestion of magnesium-containing antacids, health supplements, or laxatives may induce osmotic diarrhea typified by a stool osmotic gap (50 mosmol/L): serum osmolarity (typically 290 mosmol/kg)[2 x (fecal sodium + potassium concentration)]. Measurement of fecal osmolarity is no longer recommended since, even when measured immediately after evacuation, it may be erroneous, as. | Chapter 040. Diarrhea and Constipation Part 9 OSMOTIC CAUSES Osmotic diarrhea occurs when ingested poorly absorbable osmotically active solutes draw enough fluid into the lumen to exceed the reabsorptive capacity of the colon. Fecal water output increases in proportion to such a solute load. Osmotic diarrhea characteristically ceases with fasting or with discontinuation of the causative agent. Osmotic Laxatives Ingestion of magnesium-containing antacids health supplements or laxatives may induce osmotic diarrhea typified by a stool osmotic gap 50 mosmol L serum osmolarity typically 290 mosmol kg 2 x fecal sodium potassium concentration . Measurement of fecal osmolarity is no longer recommended since even when measured immediately after evacuation it may be erroneous as carbohydrates are metabolized by colonic bacteria causing an increase in osmolarity. Carbohydrate Malabsorption Carbohydrate malabsorption due to acquired or congenital defects in brushborder disaccharidases and other enzymes leads to osmotic diarrhea with a low pH. One of the most common causes of chronic diarrhea in adults is lactase deficiency which affects three-fourths of non-Caucasians worldwide and 5-30 of persons in the United States the total lactose load at any one time influences the symptoms experienced. Most patients learn to avoid milk products without requiring treatment with enzyme supplements. Some sugars such as sorbitol lactulose or fructose are frequently malabsorbed and diarrhea ensues with ingestion of medications gum or candies sweetened with these poorly or incompletely absorbed sugars. STEATORRHEAL CAUSES Fat malabsorption may lead to greasy foul-smelling difficult-to-flush diarrhea often associated with weight loss and nutritional deficiencies due to concomitant malabsorption of amino acids and vitamins. Increased fecal output is caused by the osmotic effects of fatty acids especially after bacterial hydroxylation and to a lesser extent by the neutral fat. Quantitatively .
