It happens

Dear Lucy: I am curious about how our bodies produce waste. I eat a fairly high-fiber diet with lots of fruits and vegetables, and my stools almost always float. My wife, a nurse, tells me that stool density—whether stools are “floaters” or “sinkers”—is sometimes used to diagnose certain diseases, particularly conditions related to the body’s inability to use fat properly. She tells me that in such conditions, fat is transferred directly to the stool, which makes it less dense and causes it to float. Should I be concerned about my floating stools, or are they just a typical byproduct of my healthy diet? —Pooped

Illustration of two logs in a pond

Dear Pooped: Lucy must say that this is one of the most interesting questions she’s ever received. Stymied but fascinated, Lucy turned to MIT Medical Gastroenterologist Richard Gardner for help.
According to Gardner, stool buoyancy is most often related to air, not fat. A high-fiber diet like yours produces more air during digestion because of increased bacterial fermentation. That air becomes trapped in the stool, making it a “floater.”
Your wife is correct that problems with fat digestion or absorption may also cause stools to float. When fat is not digested properly in the stomach and small intestine, or when fat isn’t absorbed correctly, it goes right through the GI tract. However according to Gardner, floating stools are only occasionally caused by these problems, and in such cases, the stool might also appear frothy or greasy or be particularly malodorous.
Lucy is sure her readers are on the edge of their chairs hoping to learn just how the fat content of stools can be measured. She will simply assure you that there is a simple lab test for this purpose. Said test would be ordered, along with a full medical workup, if a clinician suspected fat maldigestion or malabsorption, or if the patient had other symptoms, like anemia or unexplained weight loss.
For now, Lucy encourages you not to worry about those floaters. Keep eating that healthy diet, and check in with your healthcare provider if you still have questions or concerns. —Lucy

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