Malabsorption Syndrome: What Your Symptoms Reveal

What malabsorption syndrome is

Digestion and absorption happen in two steps. First, stomach acid, bile from the liver and enzymes from the pancreas break food into small molecules. Then the lining of the small intestine, covered in finger-like villi, absorbs those molecules into the blood.

Malabsorption syndrome can result from a fault at either step:

• Maldigestion: the food is not broken down, for example in pancreatic insufficiency or lack of bile.
• Mucosal malabsorption: the lining is damaged or missing, for example in celiac disease, Crohn's disease or after bowel removal.
• Enzyme deficiency at the lining: a single nutrient is affected, as in lactose intolerance.

The broader causes, tests and treatments are also covered on our page about intestinal malabsorption. This page focuses on reading the signs, nutrient by nutrient.

Signs by nutrient

Malabsorption due to intolerance

Sugar intolerances are the most common type of malabsorption. Unabsorbed sugar draws water into the bowel and is fermented by bacteria in the colon, producing gas.

• Lactose intolerance: low lactase enzyme. Most adults worldwide lose much of their lactase after childhood. Symptoms follow milk, ice cream and soft cheeses. Hard cheeses and yogurt are often tolerated.
• Fructose malabsorption: limited capacity to absorb fructose, found in apples, pears, honey, fruit juice and high-fructose corn syrup.
• Sugar alcohols: sorbitol, mannitol and xylitol in sugar-free gum and sweets cause gas and diarrhea in almost anyone in large amounts.
• Sucrase-isomaltase deficiency: an inherited or acquired lack of the enzyme that digests table sugar and starch. Symptoms often start in infancy.
• Secondary intolerance: gut infections, celiac disease and Crohn's disease can temporarily reduce enzymes at the gut lining. Lactose tolerance usually returns after healing.

Intolerances cause discomfort but rarely weight loss or vitamin deficiency. If those appear, look for another cause.

Other causes

• Celiac disease: immune reaction to gluten that flattens the villi. Can cause any combination of signs, or only anemia.
• Pancreatic insufficiency: from chronic pancreatitis, cystic fibrosis or pancreatic surgery; causes marked fat malabsorption.
• Small intestinal bacterial overgrowth (SIBO): bacteria in the small intestine consume nutrients and break down bile.
• Crohn's disease of the small bowel.
• Short bowel syndrome after surgery.
• Infections such as giardia, and tropical sprue in people who lived in the tropics.
• Medicines: orlistat, cholestyramine, metformin, long-term acid suppressants and some antibiotics.
• Weight-loss surgery, particularly gastric bypass.

How it is diagnosed

1. History: stool appearance, foods that trigger symptoms, weight change, surgery, alcohol and medicines.
2. Blood tests: blood count, iron, B12, folate, vitamin D, calcium, albumin, clotting time (for vitamin K) and celiac antibodies (tTG-IgA, taken while still eating gluten).
3. Stool tests: fecal elastase for pancreatic function, fecal fat, and tests for infection such as giardia.
4. Breath tests: hydrogen and methane breath tests for lactose or fructose malabsorption and bacterial overgrowth.
5. Endoscopy with small bowel biopsy to confirm celiac disease and other lining diseases.
6. Imaging: CT or MRI of the pancreas and small bowel, or capsule endoscopy.

A trial of avoiding a specific food can help confirm a sugar intolerance.

Treatment

• Treat the cause: a strict gluten-free diet for celiac disease, antibiotics for bacterial overgrowth or giardia, anti-inflammatory treatment for Crohn's disease.
• Diet changes for intolerances: reduce lactose or fructose to a tolerated level rather than cutting out whole food groups. Lactase enzyme tablets taken with dairy help many people. A dietitian can guide a low-FODMAP trial.
• Pancreatic enzyme replacement: capsules taken with every meal and snack in pancreatic insufficiency.
• Replace nutrients: iron, vitamin B12 (often by injection), folate, vitamin D, calcium and fat-soluble vitamins as needed, guided by blood tests.
• Nutrition support: high-calorie diets, medium-chain triglyceride oils that are easier to absorb, and in severe cases feeding through a vein.

Frequently asked questions

What are the symptoms of malabsorption due to intolerance?

Sugar intolerances, such as lactose or fructose intolerance, cause bloating, gas, cramping, rumbling and watery diarrhea, usually 30 minutes to 2 hours after eating the trigger food. They rarely cause weight loss or vitamin deficiencies. Symptoms depend on the amount eaten, so small portions are often tolerated.

How do I know if my body is not absorbing nutrients?

Warning signs include ongoing diarrhea, pale greasy stools that float, unexplained weight loss, fatigue from anemia, easy bruising, bone pain, tingling in the hands or feet and swollen legs. Blood tests for iron, vitamins and minerals, and stool tests, can confirm a problem and point to the cause.

Is malabsorption syndrome serious?

It can range from mild discomfort, as with lactose intolerance, to serious malnutrition, bone loss and anemia when a disease such as celiac disease or pancreatic insufficiency goes untreated. Most causes can be treated effectively once identified, so persistent symptoms deserve medical assessment.

What does fat malabsorption stool look like?

Stools are pale or clay colored, bulky, greasy or oily, unusually foul smelling and may float or be hard to flush. An oily film may appear in the toilet water. This is called steatorrhea and suggests a problem with the pancreas, bile or small intestine lining.

Can malabsorption be reversed?

Often, yes. Celiac disease improves on a gluten-free diet, bacterial overgrowth responds to antibiotics, and enzyme capsules restore fat digestion in pancreatic insufficiency. Deficiencies are corrected with supplements. Short bowel syndrome and some chronic conditions need long-term management rather than a cure.