Undigested food in stool: IBS, diarrhea, or something else?

Undigested food in a person's stool is not usually a cause for concern. The body is not able to fully break down high-fiber foods, or foods with hard shells, such as sweetcorn. Consequently, these may pass through the digestive system unchanged.

When undigested food in the stool is accompanied by another change in bowel habits, weight loss, or diarrhea, this may signal an underlying condition that needs medical attention.

In this article, we look at the various causes for undigested food to appear in stool and when a person should see their doctor.
Everyday causes

There are some reasons why food might not be completely digested that do not cause concern.
High-fiber foods
Corn and beans are more likely to be partially digested.

Fiber refers to the indigestible part of plant foods.

When a person eats high-fiber foods, it is common for some undigested material to appear in the stool because the body cannot fully break down the tough material.

Fiber also speeds up a person's bowel movements by adding bulk to the stool, which encourages the intestinal walls to move. This movement pushes food through the digestive tract.

If food moves too quickly through the digestive system, it is more likely that some foods will be less fully digested.

Certain foods are more likely than others to be partially digested and appear in the stool. These foods include:
beans
seeds
corn
peas
vegetable skins
leafy greens
certain grains
carrots
raisins
nuts

Food such as corn is a common offender. Corn has an outer shell made of an indigestible material called cellulose. The body digests the material on the inside of the corn and expels the hard outer casing in the stool.
Eating too quickly

Another harmless culprit of undigested food appearing in stool is eating too quickly. When a person eats too fast and swallows their food without fully chewing it, the food is more likely to pass through the digestive tract without being completely broken down.

Eating too quickly may force digestion to take place too rapidly, which can result in more food not being fully broken down. To avoid this, a person can slow down their eating during meals and chew their food better.
Medical conditions

While the most common cause of undigested food appearing in stool is fibrous foods, there are medical conditions that can result in whole or partially digested food in the stool. In these cases, a person often notices other symptoms, such as diarrhea or stomach pain.

Medical conditions that can cause undigested food to appear in the stool include:
Crohn's disease. This condition is a type of inflammatory bowel disease that causes inflammation in the digestive tract that can lead to severe diarrhea, abdominal pain, and malnutrition.
Celiac disease. This is an autoimmune disorder where the body cannot digest the protein known as gluten that is found in wheat, barley, and certain other grains.
Pancreatic insufficiency. If a person has a pancreatic insufficiency, they lack enzymes in the pancreas, which leads to the inability to break food down.
Lactose intolerance. If a person's digestive system is unable to break down the protein in milk and dairy, it may indicate lactose intolerance.
Irritable bowel syndrome (IBS). IBS is a common condition that affects the large intestine and causes bloating, pain, diarrhea, or constipation.

A stomach bug, or gastrointestinal virus, may also cause undigested food in the stool due to food passing quickly through a person's system. Other symptoms of a stomach bug include:
bloating
abdominal cramping
diarrhea
vomiting
nausea
body aches
malaise, or a general feeling of being unwell

In most cases of a stomach virus, symptoms will resolve in a few days when the virus has passed.
When to see a doctor
If a person has persistent abdominal pain or cramping, they should see a doctor.

A person who notices a lot of undigested food in their stool should not worry most of the time, as it is likely to be due to undigested fiber or eating too quickly.

If someone notices the following symptoms plus undigested food in their stool, they should see their doctor:
unexplained weight loss
blood in stool
changes in bowel habits
loss of control of bowels
chronic diarrhea
persistent abdominal pain or cramping
persistent bloating or gas

If a doctor suspects that a person has a digestive system condition, they may order the following diagnostic tests:
a stool sample to look for blood and other abnormalities in the stool
blood tests to look for nutritional deficiencies or inflammation markers
endoscopy to look inside the upper digestive tract
colonoscopy to examine the lower gastrointestinal tract
biopsy to check for microscopic inflammation


Most of the time, seeing undigested food in the stool is not a cause for concern. It may be the result of eating too fast or eating food with a high-fiber content.

In situations where a person has other symptoms, including abdominal pain, weight loss, or changes in bowel habits and movements, they may have an underlying medical condition.

A person who is concerned about certain symptoms or a change in their bowel movements should see a doctor to find out the cause.