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Wikipedia states that “Severe coeliac disease leads to the characteristic symptoms of pale, loose and greasy stool (steatorrhoea)”. However thumbing through the causes and the pathophysiology it did not become clear to me what leads to this key symptom.

By what mechanism does coeliac disease cause excess fat in the feces?

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2 Answers 2

Alan has covered some of it, but to add an illustration of the malabsorption piece of it, below left you can see a "normal" slice of small intestine, where the villi (finger like projections) are covered in enterocytes (the purple "bricks" along the border of the finger), which are responsible for the uptake of lipids (and their eventual "packaging") after they have been emulsified with bile salts in the intestinal lumen.

The offending gluten causes an autoimmune reaction over time that damages these villi as well as the enterocytes (as seen on the right side of the diagram), leaving a flattened area (hence far less surface area for absorption), and disrupted lipid packaging, so the unabsorbed lipids continue through the intestine into the stool.

enter image description here from Cell Biology at Yale

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So, there is no doubt that if fats are digested in the small intestine of sufferers they will not be absorbed due to the damage illustrated. However, the question remains - do the fats actually get digested at all, because if they don't then they wouldn't be absorbed anyway, even if the villi were still intact. –  Alan Boyd Jun 16 '13 at 16:10
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I always thought steatorrhea was the emulsified fats, but I may be incorrect on that. Completely undigested fats would do a greater deal of damage to the colon and rectum, I think, as was the case when they had potato chips with Olean (sp?) in the mid 1990s. –  jonsca Jun 16 '13 at 16:18

Coeliac disease is an immune disorder resulting from a reaction to ingested gluten (a protein found in wheat, barley and rye). It is associated with inflammation of the small intestine resulting in a generalised reduction in the capacity for digestion and absorption. According to this paper:

Celiac disease is associated with pancreatico-biliary disease. Postulated mechanisms include reduced gallbladder emptying due to impaired cholecystokinin release and pancreatitis due to malnutrition.

Cholecystokinin is a peptide hormone that is produced by specialised cells in the small intestine and which stimulates the production and release of pancreatic enzymes and bile. Digestion of fat is critically dependent upon the emulsifying properties of bile salts in bile, together with pancreatic lipase. Any breakdown in this stimulatory pathway would result in reduced capacity for digestion of dietary fat.

Failure to digest fat results in fatty stools (steatorrhoea) which is one of the classic symptoms of the disorder.

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I think the quoted text is quite interesting, but I'm not inclined to think that is the primary mechanism at play here. –  jonsca Jun 16 '13 at 12:33

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