When you eat fat, a small amount of the fat passes out the body through the colon. Some of the different types of fats in the feces include phospholipids, sterols, sphingolipids, cholesteryl esters, glycolipids, soaps and glycerides.  

The technical term for too much fat in your stool is steatorrhea. If excess amounts of fat are in the stool, it means the fat is not being absorbed, and there’s malabsorption. This means the fat isn’t being broken down properly by enzymes. It could be because the pancreas is not working properly (potentially due to Whipple disease or another malabsorption disorder).

The Fecal Fat test helps your doctor identify if you have pancreatic or intestinal disorders. It can also show that enzymes, which are prescribed are working in the case of known malabsorption disorders.

Normal Ranges for Fecal Fat in grams fat/24 hours:

Timed Collection:

18 years and older:  2-7 grams fat/24 hours with <20% fat in the sample

Normal ranges have not been established for patients who are <18 years old.

Infants:  < 1 gram/24 hours (with 10-40% fat in breastfed babies and 30-50% fat in bottle-fed babies)

Critical value:  > 7 grams fat/24 hours when eating a 100-150 gram fat diet shows malabsorption issues.

Random Collection: 

All ages: 0-19% fat

Note: If a timed fecal fat is done first, the test may be done over 24, 48, 72 or 96 hours. If the random fecal fat test is done, test values are recorded in percentages. If results for a random specimen are abnormal, a timed collection should be done.

Sources: 

- https://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/8310

- https://medlineplus.gov/ency/article/003588.htm 

- https://www.healthline.com/health/fecal-fat