Poop Decoder
Why is my poop yellow?
Usually fat or speed. Yellow poop often follows a greasy meal or a stomach bug that rushed things through. If it's greasy, smells foul, floats and keeps coming back, your gut may not be absorbing fat properly.
What usually causes it
Speed leaves it lighter
Bile starts out green-yellow and is broken down to brown on the way through your gut. When food moves through quickly, as with a stomach bug, there's less time for that, so stool can stay yellow or green.
Fat shows up yellow
Stool carrying a lot of undigested fat comes out pale or yellow, bulky, greasy and foul-smelling. It tends to float and can be hard to flush. Doctors call it steatorrhea.
Giardia is a classic cause
Giardia, a gut parasite, causes diarrhea with smelly, greasy poop that can float. People usually catch it from untreated lake, river or spring water, or from someone who has it. Symptoms tend to last 2 to 6 weeks, and a stool test can confirm it.
When it keeps happening
Fatty stool that goes on for weeks usually means something is stopping fat being absorbed. Celiac disease and a pancreas that doesn't make enough digestive enzymes are two well-known reasons. Both can be tested for.
Sources: The Conversation, Why is my poo green?; CDC, Symptoms of Giardia infection; StatPearls (NCBI Bookshelf), Steatorrhea; MedlinePlus, Stools: pale or clay-colored.