Okay so I came across this really interesting patho-physiologic relation between chronic fat malabsorption and renal stones which I'm going to talk about in this post.
(image from google)
First of all, what are the symptoms of malabsorption? The most common symptoms include diarrhea, weight loss, flatulence, abdominal bloating, abdominal cramps and pain. If there is predominantly fat malabsorption, the patient will have something called steatorrhea. Steatorrhea is basically presence of excess fat in the feces (obviously, because the fat is not being absorbed and staying in the intestines and eventually passing out in the stool).
What are some of the causes of chronic fat malabsorption?
There are a lot of diseases that can cause malabsorption, ranging from IBD like chron's disease, infections like whipple's disease, intestinal TB, enzyme deficiencies, for example in chronic pancreatitis, etc.
There have been quite a lot of studies that have shown a clear link between malabsorption and renal stones (couple of papers published in the NCBI journal I will be linking down below in the resources).
Now the most interesting part!! To understand the mechanism how fat malabsorption predisposes a patient to renal stones, we must first understand what is normally happening in our gut.
Without going into too much detail, if there is a proper balance between two substances, calcium ions and oxalate ions (comes mainly from green plants like spinach and other leafy green vegetables), the calcium and oxalate will bind together and form calcium oxalate. Calcium oxalate is insoluble and thus can not be absorbed and is eventually passed out with our stool.
But when there is presence of excessive fat in the gut because of malabsorption, a very interesting thing called saponification occurs. Saponification is calcium ions binding to fatty acids in the fat. Now less calcium is available to bind with the oxalate ions. The oxalate ions, if not bound with calcium are absorbable, and are absorbed in excess amounts from the gut.
This increase in oxalate levels in the blood eventually leads to increase in the amount of oxalate ions in the glomerular filtrate and urine. Increased oxalate ions in the glomerular filtrate drives the reaction between the calcium ions in the filtrate and oxalate ions causing formation of the insoluble calcium oxalate crystals. These insoluble calcium oxalate crystals eventually precipitate out forming renal stones.
Sources :
Davidson's Principles and Practice of Medicine, 22nd edition
Goljan Rapid Review Pathology, 4th edition
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3078956/
https://www.ncbi.nlm.nih.gov/pubmed/12474641
http://www.whfoods.com/genpage.php?tname=george&dbid=48
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