The Digestive Tract

The Basics

Your digestive tract, which may also be called the “gastrointestinal tract” or “GI tract,” is the route your food follows after you put it in your mouth.

illustration of the human digestive system

The GI tract is where the food you eat is turned into the nutrients your body needs to do the things you want to do. It starts with your mouth, teeth, and tongue.

Once you swallow, the food goes down your esophagus and into the stomach, where it is broken down into a pulp. From your stomach, the pulpy mixture moves into the small intestine, where the digestive enzymes and bicarbonate from the pancreas and bile from the liver help digest the food further so your body can use the nutrients in it.

The last parts of the GI tract are the large intestine, rectum, and anus — this is where the unusable bits of food you ate, along with bacteria, move out of your body.

The Pancreas

Once you chew and swallow, your food goes down the esophagus and into the stomach. The stomach makes acid that helps break down the food. Next, the food moves into the small intestine where the body starts taking the nutrients and vitamins out of the food.

To extract these nutrients, the body needs the help of the pancreas. This organ, shaped like a small fish, is attached to the small intestine behind your stomach. It is crucial for proper digestion.

The pancreas makes fluid — from 1 to 2 quarts — that mixes with the food. One part of that fluid is a product that neutralizes the acid from the stomach. It is called bicarbonate. The fluid also contains chemicals called pancreatic enzymes, which mix with the food to break them into small bits the body can absorb.

Pancreatic enzymes are very important for getting nutrients, calories, and vitamins into our bodies; they are the heart of proper digestion and absorption.

In addition to playing these important roles in the digestive process, the pancreas also makes important hormones, including insulin. Insulin works in your bloodstream, not in your intestines. It helps move glucose (sugar) from the blood into the cells so they can turn food into energy.

For many people with CF, the pancreas doesn't produce enough insulin or the body doesn't let insulin do its job, leading to CF-related diabetes (CFRD). CFRD is not caused by diet, and there is nothing you can do to prevent it.

One way to simplify this is to think of the pancreas as two separate organs: one is a digestive organ that makes pancreatic enzymes for the intestines, the other is a hormone organ that makes insulin for the body.

The healthy pancreas:

  • Makes the body's natural antacid, called bicarbonate, to mix with food coming from the stomach into the intestines.
  • Makes special chemicals called pancreatic enzymes to digest food as it moves from the stomach into the intestines.
  • Squirts fluid into the intestines to help flush food along its path through the digestive tract.
  • Makes important hormones, including insulin.

About 90 percent of people with CF have sticky mucus that blocks ducts in the pancreas and prevents enzymes from reaching the small intestine to digest food. Undigested food in the intestines can cause pain, cramping, gas, and either loose, greasy, floating stools or constipation and blockages.

Everyone with CF (including people who don't need enzyme supplements) has a pancreas that does not make enough bicarbonate to neutralize stomach acid. This can also contribute to pain, cramping, gas, and constipation. Bloating and excessive gas also can be caused by small bowel overgrowth, gastric paresis, and gastroesophageal reflux disease. 

an illustration of the human pancreas
Digestive enzymes from the pancreas are blocked and do not make it into the small intestine.


  1. Small Bowel Bacterial Overgrowth can be caused by repeated antibiotic therapy, which can kill good bacteria and cause bad bacteria to overgrow in the intestine and create gas, diarrhea, nausea, and bloating. Usually, the treatment is an antibiotic that helps tamp down bad bacteria to allow normal bacteria to regain control in the intestine.
  2. Gastric Paresis is a condition in which the stomach empties slower than normal after eating. It can cause you to get bloated and nauseous. High blood glucose can cause gastric paresis all by itself, so make sure you maintain a healthy blood glucose. Try to eat frequent, small meals throughout the day to help your stomach empty more efficiently.
  3. Gastroesophageal Reflux Disease (GERD) is caused when acid from your stomach travels backwards into the esophagus. This can be very serious if acid goes down into the lungs. You need to see a doctor if you notice heartburn or other symptoms of GERD, or if you experience repeated vomiting, fever, or weight loss.

Read the Foundation's care guidelines on pancreatic enzyme replacement.

The Liver

Among its many functions, the liver makes a fluid called bile that helps the body absorb fat. Bile travels through small tubes or ducts in the liver and is stored in the gallbladder, which empties the bile into the small intestine.
In some people with CF, bile gets thick and flows very slowly. It can even get so thick that it forms stones in the gallbladder, which sometimes need to be removed. You can still have normal digestion if your gallbladder has been removed.

As the mixture of food, pancreatic fluid, bile and pancreatic enzymes moves along the small intestine, the important nutrients make their way into the body by absorption through special cells in the walls of the small intestine.

  • Liver disease is advanced scarring (fibrosis) in the liver. The medical term is cirrhosis.
  • According to CF Foundation Guidelines, individuals with CF should get liver function tests annually. These blood tests show whether there is inflammation.
  • Only 5-10 percent of people with CF develop CF liver disease.
  • Virtually all people with CF liver disease are diagnosed by age 15. Over half are diagnosed by age 10. CF liver disease is rarely diagnosed in adults.
  • Reduce the chances of liver problems by getting vaccinated for hepatitis A and B, avoid excessive alcohol use and IV drug use, and maintain good nutrition.
The Large Intestine

Below the small intestine comes the large intestine. A few nutrients are taken in by the large intestine, but its more important function is to keep the balance of fluid just right in the mass of what remains of the digested food.

The very end of the large intestine is called the rectum. This is where the mass of fully digested food and bacteria leaves your body in the form of stool, or bowel movement. As you probably know by now, your care team will usually ask you about your bowel movements.

Myth Busters

  • Not taking enzymes is a good way to treat constipation because your stools get looser when you don't take enzymes.”

    False. Not taking your enzymes puts you at increased risk of having constipation or a bowel obstruction. If you are getting constipated or straining to move your bowels, keep taking or make sure you never miss taking your enzymes. Also, make sure you are drinking enough fluids every day. You may need a medication to draw water into the intestines to loosen stools or to thin mucus along the intestinal wall.
  • “I have bowel movements every day, so I can't be constipated.”

    False. People with CF who are constipated almost always have bowel movements every day, often more than once a day. Symptoms of constipation include bloating, bloody stools, poor weight gain, poor appetite, “overflow” diarrhea, and rectal prolapse.
  • “My doctor told me I have a working pancreas (pancreatic sufficient), so I have a normal GI tract.”

    False. You may still be prone to constipation, and you should still eat a high-fiber diet with plenty of fluids. You may also need medication to loosen stools or thin the mucus along the intestinal wall. Also, your pancreas is still sensitive to injury, so drinking excessive amounts of alcohol (binge drinking) can change you from someone with a working pancreas to someone whose pancreas doesn't work correctly.
What Research Is Being Done?

The CF Foundation supports research focusing on the treatment of GI issues in CF.

Share this article
8 min read