They are often called “ghost poops” — bowel movements that leave almost no trace in the toilet bowl. Rather than being a reason to panic, these elusive stools may sometimes reflect a well-functioning digestive system.
Scientists caution, however, that persistent changes in stool buoyancy can also point to underlying problems. Understanding when floating stools are normal and when they may warrant attention has become an active area of gut health research.
Why some stools float or sink
Stool buoyancy largely depends on its gas and water content. Research dating back to the 1970s showed that floating stools typically contain more trapped gas, particularly methane, while sinking stools contain less.
When scientists removed gas from samples in early studies, previously floating and sinking stools became similar in density. This suggested that additional gas or water, rather than fiber or undigested food alone, largely determines whether stools float or sink.
The role of gut microbes and gas
Gas in stool is closely connected to the gut microbiome. Certain bacteria in the colon break down fiber and other components of food, releasing gases such as methane, hydrogen and carbon dioxide as natural byproducts of fermentation.
In a 2022 mouse study, animals raised completely germ-free produced only sinking stools. Once researchers introduced normal gut microbes into their intestines, the same mice began producing floating stools, highlighting the role microbes can play in stool buoyancy.
When floating stools may signal trouble
Occasional floating stools in otherwise healthy people are generally harmless. However, repeated floating stools, particularly when they are pale, oily or foul-smelling, can indicate poor fat absorption, known as steatorrhea.
Fatty stools can be associated with conditions including celiac disease, chronic pancreatitis, inflammatory bowel disease and bile duct problems. Poor absorption may also reduce levels of fat-soluble vitamins such as A, D, E and K over time.
Clinical research provides additional clues. A 2015 analysis found that floating stools were reported more frequently by people with functional bowel disorders, particularly mixed-type irritable bowel syndrome, compared with other gastrointestinal conditions.
In a 2018 study involving people with type 1 diabetes, self-reported floating stools were more common than among healthy controls. Researchers suggested that long-term diabetes-related damage to the gut could play a role, although they stressed that stool buoyancy alone is not diagnostic.
Diet, fiber and healthy fermentation
Diet strongly influences the gut microbiome and the gases it produces. A 2021 randomized trial involving healthy men found that switching from a standard Western diet to a fiber-rich Mediterranean-style diet increased intestinal gas and post-meal flatulence.
Despite the additional gas, the Mediterranean diet is widely considered beneficial, supporting microbial diversity and the production of short-chain fatty acids that nourish the gut lining. In this context, increased gas can reflect active fermentation of dietary fiber.
Still, balance is important. Excessive gas, bloating, pain or sudden and persistent changes in stool appearance or buoyancy warrant medical advice, particularly when accompanied by weight loss, blood in the stool or ongoing diarrhea.
Why watching your stool matters
Colorectal specialists emphasize that paying attention to bowel movements can be a simple form of self-monitoring. Color, consistency, frequency and buoyancy together provide a more complete picture than any single characteristic on its own.
Doctors recommend seeking medical evaluation when noticeable changes persist for more than a few weeks. Early investigation can help identify conditions ranging from food intolerances to more serious illnesses such as colorectal cancer or chronic pancreatic disease.
For most people, however, an occasional “ghost poop” is simply another quirk of the digestive system. As research into the gut microbiome advances, these everyday observations may provide increasingly useful clues about what is happening inside the gut.
