What is malabsorption?

Short answer

MedlinePlus says malabsorption means your body is not properly absorbing fats or other nutrients. It’s not a single disease but a result, and the cause matters most. The NIH lists these signs:

Sign (NIH)	What you might notice
Bloating	A full, swollen feeling
Gas	More wind than usual
Changes in appetite	Eating more or less
Loose, greasy, foul-smelling bowel movements	Poop that’s hard to flush or leaves an oily film
Weight loss	Or poor weight gain in children

One sign alone, on one day, usually means very little. A pattern of several, especially with weight loss, needs a doctor.

What causes malabsorption?

Cause	What the source says
Coeliac disease	The NHS says the immune system attacks the small intestine, so it can’t properly take in nutrients. Triggered by gluten in wheat, barley and rye.
Chronic pancreatitis	MedlinePlus says in conditions such as long-term pancreatitis, the fat content of stool is increased.
After a gut infection	The NIH says after some infections you may have problems digesting certain carbohydrates, which can make diarrhea last longer.
Carbohydrate problems	The NIH says some people have problems digesting certain carbohydrates, which can cause chronic diarrhea.

The NHS says coeliac disease affects at least 1 in 100 people in the UK, and first-degree relatives (parents, brothers, sisters and children) of people with it should be tested. Its symptoms can include diarrhea that may smell particularly unpleasant, tummy pain, bloating, tiredness and unintentional weight loss.

Is floating or smelly poop a sign?

Sometimes, but usually not. MedlinePlus says:

• most floating stools come from what you eat, because a diet change can increase gas
• floating stools can also happen with a gut infection
• most causes are harmless and go away without treatment
• floating, greasy, foul-smelling stools may be due to severe fat malabsorption, particularly if you are losing weight

On smell, MedlinePlus says diet is the usual reason, but celiac disease and blood in the stool are also on its list of causes. More in floating poop and smelly poop.

Probably diet	Worth a doctor’s look
Floats once after a big change in food	Floats, looks greasy and smells foul, often
Smell changes after a specific meal	Comes with weight loss
Settles in a few days	Comes with ongoing diarrhea, blood, or black or pale stools

How do doctors check?

MedlinePlus says your provider may ask about your usual diet and whether a change in diet changes your stools. Fecal fat and fecal elastase tests may be done, and blood tests too, though in most cases of floating stools they aren’t needed.

For coeliac disease, the NHS says the first step is a blood test. Keep eating gluten while being tested, because avoiding it could give an inaccurate result. Don’t start a gluten-free diet until a specialist confirms the diagnosis, even if the blood test is positive. See coeliac disease or IBS.

How do I track it?

PoopAI logs each poop by Bristol type with an optional photo, and meals by photo or text with trigger tags like gluten and dairy. It doesn’t record weight, smell or appetite, so add those as paper notes.

Mon 08:20  Poop: type 6, photo added
Paper note: greasy film, hard to flush, smelled foul
Mon 13:00  Meal: toast, cheese omelet  tags: gluten, dairy
Paper note: weight down 2 kg this month without trying
Tue 08:05  Poop: type 6, photo added

Keep eating your normal diet while you log if tests might follow. That’s what makes them accurate.

Malabsorption myths vs facts

Myth	Fact
“Floating poop means I’m not absorbing food.”	MedlinePlus says most floating stools come from diet and gas.
“I’ll cut out gluten first and see.”	The NHS says keep eating gluten until coeliac testing is done.
“Smelly poop is always a problem.”	MedlinePlus says diet is the usual reason.
“Only adults get it.”	The NIH lists poor weight gain in children as a sign.

Before seeing a GP

• Log Bristol types for 2 weeks, with photos if you're comfortable
• Note greasy, floating or foul-smelling stools
• Note any weight change, appetite change or tiredness
• Keep eating gluten until coeliac tests are done
• Note any family history of coeliac disease

When should I get help?

• Tell your provider about changes in your stools or bowel movements (MedlinePlus).
• Contact a provider right away for bloody stools with weight loss, dizziness and fever (MedlinePlus).
• Contact a provider if you have black or pale stools often (MedlinePlus).
• Ask for an urgent GP appointment or call 111 if your poo is black or dark red, or you have bloody diarrhea (NHS).
• Call 999 or go to A&E if you’re bleeding non-stop or there’s a lot of blood (NHS).

Where does PoopAI fit?

PoopAI gives you a dated record of Bristol types, optional photos and meals, with weekly reports and trend charts. It can’t detect malabsorption. It can make it easier to show a doctor what changed and when.

Bottom line

Malabsorption means your body isn’t taking in fats or nutrients properly. Greasy, foul, floating stools with weight loss are the classic warning pattern. Most odd-looking poop is diet, but repeated signs need a doctor, and coeliac testing needs gluten still in your diet.

Editorial note: Written by The FixMyGut team using the NIH, MedlinePlus and NHS sources listed below. It’s general information, not a diagnosis. Facts checked against those sources on November 5, 2026.