What to Know About Undigested Food in Your Stool

Medically Reviewed by Minesh Khatri, MD on September 11, 2023
Written by WebMD Editorial Contributor
3 min read

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.

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:

  • Nuts
  • Seeds
  • Corn
  • Vegetable skins

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.

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)
  • Pancreas problems
  • Celiac disease
  • Inflammatory bowel disease (IBD)
  • 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.

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 ulcerative 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

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:

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.