Know Which Foods to Avoid Before Giving a Stool Sample

If you are having digestive symptoms, your doctor may prescribe an at-home stool test, in which you collect stool samples and send them to a lab or bring them to your doctor’s office for analysis. Stool samples are used for routine screenings and can also help diagnose various diseases involving the gastrointestinal tract or pancreas.

There are different types of stool tests, some of which may require you to avoid certain foods or medications before you start collecting samples. Your healthcare provider will give you specific instructions on how to prepare and let you know whether there are any foods you need to avoid or consume in order to get accurate results.

Stool Tests for Blood

Stool tests for blood are commonly done to screen for colon cancer or other digestive system problems. Two types of tests are used: the less commonly used fecal occult blood test (FOBT) and the fecal immunochemical test (FIT). The FOBT checks for a protein found in red blood cells; to get an accurate result, you will provide three samples over the course of a few days.

Some foods, medications, and vitamins can interfere with the FOBT and its results. For this reason, you will need to avoid certain foods for a few days before the test. According to Memorial Sloan Kettering Cancer Center (MSK), you should avoid consuming the following foods and medications for three days before collecting stool samples for the FOBT:

• Red meat, such as beef, lamb, or liver
• Raw fruits and vegetables that contain peroxidases (a group of enzymes), such as horseradish, turnips and broccoli
• Foods containing vitamin C, such as fruit juices with vitamin C, and vitamin C supplements in doses higher than 250 milligrams per day

Most people will need to stop taking aspirin, other nonsteroidal anti-inflammatory drugs, and vitamin E before and during the three-day collection period, according to MSK, as these medications may cause small amounts of blood to appear in your stool. For FIT tests, there are no dietary adjustments that are needed.

Fecal Fat Test

The fecal fat test checks for an excess amount of fat in the stool, which can indicate that food is moving through your digestive system without being broken down and absorbed correctly, according to the University of Rochester Medical Center (URMC). This is called malabsorption. The URMC says that a fecal fat test is used to help diagnose diseases including celiac disease, Crohn’s disease, cystic fibrosis, and diseases of the pancreas.

On the day or days that you collect stool for this test, you must consume 100 grams of fat, according to Stanford University Medical Center. Your healthcare provider will advise you on what foods to eat to reach this amount and tell you if there are any foods or medications you should avoid.

Other Stool Tests

Although many stool tests do not require dietary restrictions, you might need to fast for some of them. People with watery diarrhea may undergo stool electrolyte and osmolality tests, which are generally not affected by specific foods but may require fasting in some cases, says Testing.com. Typically, there are no dietary restrictions on tests for gastrointestinal infections, such as a stool culture or a test for parasites, according to Testing.com. Other stool tests not affected by your diet include fecal trypsin and chymotrypsin — which are used to check pancreatic function in people with cystic fibrosis — and lactoferrin and calprotectin, which are used to test for inflammation of the bowel.