Fecal Fat


The fecal fat test measures the amount of fat in the stool. This can help gauge the percentage of dietary fat that the body does not absorb.

Alternative Names

Quantitative stool fat determination; Fat absorption

How the Test is Performed

There are many ways to collect the samples.

  • For adults and children, you can catch the stool on plastic wrap that is loosely placed over the toilet bowl and held in place by the toilet seat. Then put the sample in a clean container. One test kit supplies a special toilet tissue that you use to collect the sample, then put the sample in a clean container.
  • For infants and children wearing diapers, you can line the diaper with plastic wrap. If the plastic wrap is placed properly, you can prevent mixing of urine and stool. This will provide a better sample.

Collect all stool that is released over a 24-hour period (or sometimes 3 days) in the containers provided. Label the containers with name, time, and date, and send them to the lab.

How to Prepare for the Test

Eat a normal diet containing about 100 grams (g) of fat per day for 3 days before starting the test. The health care provider may ask you to stop using drugs or food additives that could affect the test.

How the Test will Feel

The test involves only normal bowel movements. There is no discomfort.

Why the Test is Performed

This test evaluates fat absorption to tell how well the liver, gallbladder, pancreas, and intestines are working.

Fat malabsorption can cause a change in your stools called steatorrhea. To absorb fat normally, the body needs bile from the gallbladder (or liver if the gallbladder has been removed), enzymes from the pancreas, and normal intestines.

Normal Results

Less than 7 g of fat per 24 hours.

What Abnormal Results Mean

Decreased fat absorption may be caused by:

  • Biliary cancer
  • Biliary stricture
  • Celiac disease
  • Chronic pancreatitis
  • Crohn disease
  • Cystic fibrosis
  • Gallstones (cholelithiasis)
  • Pancreatic cancer
  • Pancreatitis
  • Radiation enteritis
  • Short bowel syndrome (for example from surgery or an inherited problem)
  • Sprue
  • Whipple disease
  • Small bowel bacterial overgrowth


There are no risks.


Factors that interfere with the test are:

  • Enemas
  • Laxatives
  • Mineral oil


Hogenauer C, Hammer HF. Maldigestion and malabsorption. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger & Fordtran's Gastrointestinal and Liver Disease. 10th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 104.

Semrad CE. Approach to the patient with diarrhea and malabsorption. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 140.

Review Date: 7/22/2016

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. Copyright ©2017 A.D.A.M., Inc., as modified by University of California San Francisco. Any duplication or distribution of the information contained herein is strictly prohibited.

Information developed by A.D.A.M., Inc. regarding tests and test results may not directly correspond with information provided by UCSF Medical Center. Please discuss with your doctor any questions or concerns you may have.