If someone notices the following symptoms plus undigested food in their stool, they should speak with a doctor:
Why does undigested food appear in stool, and when is it a cause for concern?
Foods that are high in fiber or have hard shells, like sweetcorn, often pass through the body undigested. This is because they are hard to break down. However, other undigested foods in stool could indicate an underlying condition, such as Crohn’s disease.
When undigested food in the stool occurs with a change in bowel habits, weight loss, or diarrhea, this may signal an underlying condition that needs medical attention.
In this article, we look at reasons why undigested food may appear in stool and when a person should speak with a doctor.
There are some reasons why the body might not completely digest foods that do not cause concern.
Undigested food can appear in the stool if there is material in food that is indigestible, such as cellulose in some high-fiber foods. This could be due to a person not chewing the food well or the food containing shells or skins that the body’s natural enzymes cannot break down.
It could also happen if food passes too quickly through the digestive system, for example, if the person has a condition such as Crohn’s disease, which causes inflammation in the digestive system. It can also happen if someone has gastric surgery or a bowel resection.
High-fiber foods
Fiber refers to the indigestible part of plant foods. A high-fiber diet can have many benefits, including keeping the digestive system healthy and keeping bowel movements regular.
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, a person may not fully digest some foods.
Certain foods are more likely than others to be difficult to fully digest. These foods include:
Foods such as corn often remain partially undigested. Corn has an outer shell made of an indigestible material called cellulose. The body digests the material 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, 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, resulting in more food not being fully broken down. To avoid this, a person can slow down their eating during meals and chew their food for longer.
The most common cause of undigested food appearing in stool is fibrous foods, but some medical conditions can result in whole or partially digested food appearing in stool. In these cases, a person often notices other symptoms, such as diarrhea or stomach pain.
Medical conditions that may cause undigested food to appear in the stool include the following:
Crohn’s disease
This condition is a type of inflammatory bowel disease that causes inflammation in the digestive tract.
- severe diarrhea
- nausea
- abdominal pain and cramps
- weight loss and low appetite
- anemia
- fatigue
- fever
- red or sore eyes
- joint pain
- tender bumps under the skin
In some cases, undigested food may appear in a person’s stool.
Celiac disease
This is an autoimmune disorder where the body cannot digest the protein known as gluten, which occurs in wheat, barley, and other grains.
- bloating and abdominal pain
- diarrhea
- constipation
- gas
- stools that are loose, greasy, bulky, and smell foul
- lactose intolerance
Some people may notice undigested food in their stool.
Pancreatic insufficiency
A person with pancreatic insufficiency lacks enzymes in the pancreas, making it hard to break down food. This could lead to undigested food appearing in stool.
Symptoms of this condition include:
- abdominal discomfort and bloating
- weight loss
- fatty stools
- nutritional deficiencies, leading to muscle spasms, bone disease, and a higher risk of cardiovascular problems
Lactose intolerance
If a person’s digestive system cannot break down the protein in milk and dairy, it may indicate lactose intolerance.
- bloating and gas
- diarrhea
- nausea and vomiting
- abdominal pain
- “growling” in the stomach
Undigested food could appear in the stool of people with lactose intolerance.
Irritable bowel syndrome (IBS)
IBS is a common condition that affects the large intestine.
- bloating and pain
- diarrhea, constipation, or both
- the feeling that a bowel movement is unfinished
- white mucus in the stool
Some people may also notice undigested food in their stool.
Gastroenteritis, or a “stomach bug”
A stomach bug, stomach flu, or gastrointestinal virus may 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
- watery diarrhea
- vomiting
- nausea
- fever, in some cases
- dehydration, which can lead to dark-colored urine, thirst, less frequent urination, faintness, and fatigue
In most cases of a stomach virus, symptoms will resolve in a few days when the virus has passed. However, dehydration can quickly become serious. People should seek medical help at once if they or someone else has signs of dehydration or experiences:
- severe pain or worsening symptoms
- changes in mental state or consciousness
- six or more loose stools in a day
- diarrhea lasting more than 2 days
- blood or pus in stool
There is a possibility that undigested food could appear in the stool.
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 speak with a 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
- signs of dehydration, such as increased thirst or reduced urination
If a doctor suspects that a person has a condition affecting their digestive system, they may order the following diagnostic tests:
- a stool sample to look for blood and other abnormalities
- 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
A high-fiber diet is a healthy option for most people, and there is no need for concern if some food particles remain undigested.
However, if the body cannot digest food due to an underlying condition, a doctor will recommend treatment to address the problem.
Depending on the cause, they may recommend medication, dietary changes, or surgery in some cases.
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 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 has concerns about certain symptoms or changes in their bowel movements should speak with a doctor.
Last medically reviewed on November 5, 2021
- Irritable Bowel Syndrome
- Crohn’s / IBD
- GastroIntestinal / Gastroenterology
- Nutrition / Diet
How we reviewed this article:
Medical News Today has strict sourcing guidelines and draws only from peer-reviewed studies, academic research institutions, and medical journals and associations. We avoid using tertiary references. We link primary sources — including studies, scientific references, and statistics — within each article and also list them in the resources section at the bottom of our articles. You can learn more about how we ensure our content is accurate and current by reading our editorial policy.
- Ghodeif, A. O., et al. (2021). Pancreatic insufficiency.
https://www.ncbi.nlm.nih.gov/books/NBK555926/ - Symptoms and causes of celiac disease. (2020).
https://www.niddk.nih.gov/health-information/digestive-diseases/celiac-disease/symptoms-causes - Symptoms and causes of Crohn’s disease. (2017).
https://www.niddk.nih.gov/health-information/digestive-diseases/crohns-disease/symptoms-causes - Symptoms and causes of irritable bowel syndrome. (2017).
https://www.niddk.nih.gov/health-information/digestive-diseases/irritable-bowel-syndrome/symptoms-causes - Symptoms and causes of lactose intolerance. (2018).
https://www.niddk.nih.gov/health-information/digestive-diseases/lactose-intolerance/symptoms-causes - Symptoms and causes of viral gastroenteritis (“stomach flu”). (2018).
https://www.niddk.nih.gov/health-information/digestive-diseases/viral-gastroenteritis/symptoms-causes#gastroenteritissymptoms
What to Know About Undigested Food in Your Stool
It’s perfectly normal to sometimes see some undigested food in your stool. But if you have other symptoms, it might be a sign of a health problem.
Is It Normal to Have Undigested Food in Your Stool?
Your gastrointestinal system, or GI tract, is a system of organs that helps you digest foods and absorb nutrients.
When you eat, the food is partially digested in your stomach. It then moves into your small intestine, where the nutrients and vitamins are absorbed. The leftover waste travels into your large intestine, then out of your body as poop.
Your large intestine absorbs water from your stool. If food passes through too quickly, too little water is absorbed and you might have diarrhea. If it passes too slowly, your body absorbs too much water and you may become constipated.
Your body can’t fully digest foods high in fiber, a type of carbohydrate. While your body breaks down most carbohydrates into sugar molecules, it can’t break down fiber. So it passes through your GI tract undigested.
Fiber adds bulk and absorbs water, which makes stool softer and easier to pass. This makes it very useful for constipation. It also has many health benefits. For example, it helps protect you against colon cancer and digestive disorders like IBS.
Foods that are high in fiber include:
- Beans and legumes
- Whole grains
- Vegetable and fruit peels
- Seeds
- Raspberries
- Leafy, green vegetables
- Spinach
- Celery
- Broccoli
- Root vegetables
- Potatoes
- Turnips
- Carrots
You might see some parts of these foods in your stool:
Corn might look untouched when it passes out in your stool. But your body does digest parts of it. The outer skin of the kernel contains cellulose, which your body can’t break down. It can digest nutrients inside the kernel, though.
What Causes Undigested Food in Your Stool?
Sometimes problems in your digestive tract and other health conditions can cause undigested food in your stool. Your doctor might call this malabsorption. Conditions that can cause it include:
- Small intestinal bacterial overgrowth (SIBO)
- Diverticulitis
- Pancreas problems
- Celiac disease
- Inflammatory bowel disease (IBD)
- Crohn’s disease
- Colitis
- Cystic fibrosis
- Lactose intolerance
Small intestine overgrowth. The small intestine naturally has some bacteria. They’re important for B12 absorption, among other things. Sometimes they can grow too much, causing problems like damage to your intestines, malabsorption, poor fat absorption, and vitamin deficiencies.
Diverticulitis. Diverticulosis happens when small pouches bulge out of the sides of your intestine. Food can get stuck in these pouches, causing them to become infected, which leads to diverticulitis.
Pancreas problems. Your pancreas releases enzymes that help you digest fats and foods. If you have pancreatic cancer, pancreatic insufficiency, or cystic fibrosis that causes mucus plugs in your pancreas, you can have problems digesting food.
Celiac disease. Celiac disease is an autoimmune disease in which your body reacts to gluten, a protein found in wheat and some other foods. Over time, your intestine becomes damaged and you might have trouble digesting food. This can cause malnutrition.
IBD. Autoimmune diseases like Crohn’s and colitis are inflammatory bowel diseases that can damage the intestine and cause poor food breakdown and absorption.
Lactose intolerance. Some people don’t make the enzyme lactase, which helps your body break down a sugar found in milk and milk products (lactose). This can cause problems digesting these foods.
All of these conditions have other symptoms besides undigested food in the stool. Depending on the condition, they may include:
- Diarrhea
- Light-colored stool
- Foul-smelling stool
- Greasy stool
- Constipation
- Gas
- Bloating
- Cramping
- Pain
- Fever
Risks of Malabsorption
Most of the time, undigested food doesn’t mean you have a health problem. But sometimes, if you have another health condition or have other symptoms like diarrhea, it can lead to health issues.
Undigested food could mean you’re not absorbing nutrients, vitamins, and minerals. You can have trouble getting enough vitamins like B12 and key minerals like iron that keep your body working.
Malnutrition can lead to:
- Weight loss
- Tiredness
- Depression
- Irritability
- Headaches
- Weakness
- Heart palpitations
- Changes in how you think and behave
When to See Your Doctor
It’s normal to have some undigested food in your stool, especially when you eat high-fiber foods. If you don’t have any other symptoms, you probably don’t need to worry.
If you notice undigested food along with these other symptoms, see your doctor:
- Frequent diarrhea
- Blood in your stool
- Fevers
- Light-colored stool
- Loss of bowel control
- Tiredness
- Unexplained weight loss
If you already have other health problems like cystic fibrosis and you notice gut problems, make sure to talk to your doctor.
Show Sources
Advances in Physiology Education: “Corn? When did I eat corn? Gastrointestinal transit time in health science students.”
Colon & Rectal Surgery Associates: “High-Fiber Diet.”
Cystic Fibrosis Foundation: “The Digestive Tract.”
Harvard School of Public Health: “Fiber.”
M Health: “Gastrointestinal Complications.”
Merck Manuals Consumer Version: “Overview of Malabsorption,” “Small Intestinal Bacterial Overgrowth (SIBO).”
NHS: “Malnutrition,” “Vitamin B12 or folate deficiency anaemia – Symptoms.”
SCL Health: “Diverticulitis.”
St. Clair Health: “Undigested food in stool: What does it mean?”
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