Fecal Fat Testing

Written by Erica Roth | Published on August 7, 2012
Medically Reviewed by George Krucik, MD

What is a Fecal Fat Test?

A fecal fat test measures the amount of fat in your feces or stool. The concentration of fat in your stool can tell doctors how much fat your body absorbs during digestion. Changes in stool consistency and odor can indicate that your body is not absorbing as much fat as it should.

Fecal fat testing usually spans 24 hours, but can sometimes last for three days. During the testing period, you will need to collect each stool sample with a special testing kit. Your local laboratory will provide you with the testing kit and specific instructions about usage. Some fecal test kits require you to collect the samples with plastic wrap. Others include special toilet paper or plastic cups.

Purposes of Fecal Fat Testing

Fecal fat testing might be performed if your doctor suspects that your digestive system is not functioning correctly. In a normal person, the absorption of fat is based on a variety of factors:

  • bile production in the gallbladder or liver, if your gallbladder was removed
  • production of digestion enzymes in the pancreas
  • normal functioning of the intestines

If any of these organs are not working properly, your body might not be able to absorb as much fat as you need to remain healthy and nourished. Decreased absorption of fat can be a sign of many different illnesses, including:

  • celiac disease: damage to the intestinal lining caused by an allergy to gluten
  • Crohn’s disease: an autoimmune inflammatory bowel disease affecting the entire digestive tract
  • cystic fibrosis: a genetic disease resulting in thick mucus secretions in the lungs and digestive tract
  • pancreatitis: inflammation of the pancreas
  • cancer: tumors in the pancreas or biliary ducts

People who have decreased absorption of fat often notice changes in their bowel habits. This is because the fat that is not digested is excreted in the feces. You might notice your stool is looser, almost diarrhea-like in consistency. Stool with a high fat content also emits a fouler-than-normal odor and is likely to float.

Preparing for Fecal Fat Testing

Everyone who undergoes fecal fat testing is required to follow a high-fat diet for three days prior to the test. This allows for the accurate measurement of the fat concentration in the stool. You will be asked to eat 100 grams of fat each day for three days before taking the fecal fat test. This is not as difficult as one might think: two cups of whole milk, for example, contains 20 grams of fat, and eight ounces of lean meat contains approximately 24 grams of fat.

Your doctor or dietitian may help you determine how to eat the required fat each day. You might be given a list of suggested foods to help you plan your meals. Whole milk, full-fat yogurt, and cheese can boost your fat intake. Beef, eggs, peanut butter, nuts, and baked goods are also good sources of fat. Reading the nutrition labels of the foods in your pantry gives you an idea of how much fat you consume in each meal or snack. If you tend to eat more than 100 grams of fat each day, the dietitian will teach you how to cut fat out of your diet and make healthier choices.

After following the high-fat diet for three days, you will return to a normal diet and begin the stool collection process. Have the collection kit ready at home for the first day of testing.

Fecal Fat Testing Procedure

You need to collect the stool each time you have a bowel movement during your testing period. You might be given a plastic “hat” to place over the toilet bowl, or directed to loosely cover the bowl with plastic wrap. Urinate before you place the hat or plastic over the toilet bowl. Urine, water, and regular toilet paper can contaminate your sample and render the test results inaccurate.

After the collection apparatus is in place, collect your stool sample. You may be given additional tools, like a wooden or plastic scoop, to transfer the sample into a special container. Cover the container tightly and place either in the refrigerator, freezer, or in a separate cooler that is insulated and filled with ice. Repeat the process each time you have a bowel movement during the 24- or 72-hour testing period.

Fecal Fat Testing for Children

Line the diaper of babies and toddlers with plastic wrap to carry out fecal fat testing. Try to place the plastic in the back portion of the diaper to prevent the mixing of feces and urine.

When you have completed the fecal fat testing, write your name, date, and time on the container. Return the sample container to the lab.

Interpreting the Results of Fecal Fat Testing

The normal range for fecal fat testing is 7 grams over a 24-hour period. Normal results for a 72-hour test would be 21 grams. Your doctor will review results that are lower than normal. You might undergo further testing based on your medical history and symptoms to determine why your fecal fat concentration is low.

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