Diarrhea is when someone has loose, watery stools or bowel movements. When this occurs after eating, it is known as postprandial diarrhea (PD), which can happen quite unexpectedly. It can also cause discomfort or pain until a bowel movement occurs.

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PD is relatively common, but it may be difficult to figure out what is causing it and how to treat it. The reason for this is that PD can be a sign of a medical condition, or it can just happen with no specific cause.

Diarrhea is either acute or chronic, depending on how long the symptoms last. Acute diarrhea lasts for only a couple of days or weeks. Chronic diarrhea, on the other hand, can last for several weeks or months.

This article discusses the causes of both acute and chronic PD, along with what a person can do to treat and prevent them.

How often diarrhea occurs can vary greatly and depends on the underlying cause. The following are the prevalence rates of some common causes of diarrhea following eating. A person may not necessarily experience diarrhea, but diarrhea can be a symptom of each condition:

  • Food poisoning: 1 in 6 people get food poisoning each year.
  • Lactose intolerance: The prevalence varies greatly, with it affecting about 5% of people of northern European descent and possibly up to 90% of people of Hispanic, African, or Asian descent.
  • Inflammatory bowel disease (IBD): 2015 data from the Centers for Disease Control and Prevention (CDC) indicates that about 3 million adults in the United States report living with IBD.
  • Irritable Bowel Syndrome (IBS): Worldwide, IBS affects approximately 10–15% of individuals and is the most common GI disorder that gastroenterologists diagnose.
  • Antibiotic side effects: A 2015 study found a prevalence rate of about 9.6% for antibiotic-associated diarrhea.
  • Celiac disease: This affects about 1 in 133 Americans, or 1% of the U.S. population.
  • Viral gastroenteritis (stomach flu, norovirus): This affects about 19–21 million Americans every year.

There are many different causes of PD or diarrhea after eating, depending on whether it is acute or chronic.

Acute PD

Acute diarrhea usually lasts for 1–2 days. Doctors either treat it with medicine or leave it to run its course. Its causes include:

Food poisoning

Contaminated food or water can cause diarrhea. Bacteria, viruses, parasites, or other organisms can cause contamination and lead to illness. Viruses and bacteria are the leading causes of food poisoning in the U.S.

Infection

Viral gastroenteritis, also known as “stomach flu,” can cause diarrhea and vomiting. “Flu” is a misnomer as this type of infection has nothing to do with influenza. Instead, the most common cause of viral gastroenteritis is norovirus.

Gastrocolic reflex

Gastrocolic reflex is a physiological reflex where consuming food causes the rectum to respond by moving stool. The intensity of the movement can vary between people. Doctors can use this phenomenon to help relieve constipation in children and older people by establishing a routine of passing a bowel movement after eating. It is a relatively common occurrence, but it does not typically cause diarrhea.

Lactose intolerance

Some people have an allergy to milk or are not able to digest lactose, which is the sugar in milk. This means that if they drink or eat milk, it can cause diarrhea, cramping, and gas. Lactose intolerance has a higher prevalence rate in people with Asian, African, or Hispanic ancestry compared with those with northern European ancestry.

Toddler’s diarrhea

Acute diarrhea is common in young children between the ages of about 6 months and 5 years. Although doctors do not know the exact cause, theories include children who experience it moving food through their bowels faster, which does not allow for as much water absorption. Another theory is that it occurs in children who drink a lot of sugary drinks, such as fruit juice. The high amount of sugar causes water to enter the intestines, making the stool more watery.

Antibiotics

Some antibiotics can cause an upset stomach and acute diarrhea. The symptoms tend to resolve once the person stops taking antibiotics.

Parasites

Some parasites can cause acute diarrhea. The symptoms tend to last until a doctor identifies and removes the parasite.

These types of parasites are not common in developed countries and people usually contract them while traveling. The most common parasites in the U.S. include roundworm, protozoa, and tapeworms.

Chronic PD

Chronic diarrhea is diarrhea that lasts for at least 4 weeks, with a minimum of three loose or watery bowel movements each day. Potential causes of chronic diarrhea include:

Irritable bowel syndrome

IBS is a disorder that can cause bloating, cramping, and either constipation (IBS-C) or diarrhea (IBS-D). It is the most common GI disorder, with a 10–15% worldwide prevalence rate. Dietary changes, medication, and stress management strategies can often help a person control the condition.

Inflammatory bowel disease

IBD is an autoimmune condition where the immune system attacks otherwise healthy cells of the intestines, causing inflammation and irritability in the intestines.

Crohn’s disease and ulcerative colitis are two examples of IBD. Both can cause persistent diarrhea, cramping, weight loss, and tiredness.

Endocrine disorders

Some hormonal disorders, such as hyperthyroidism and diabetes, can cause chronic diarrhea, especially if there is nerve damage to the intestinal tract.

Celiac disease

Celiac disease is an autoimmune disorder that affects the absorption of gluten, the protein found in wheat and wheat products.

People with this condition have diarrhea whenever they eat food that contains gluten from wheat, barley, or rye. Several products may contain gluten, including pasta, bread, sauces, gravies, and other products a person may not immediately think about. A person should check the label of prepared foods to see if they contain gluten.

In most cases of acute diarrhea, the symptoms go away over time, and a person can manage them at home.

Home care

Home care often includes a combination of hydration, bland foods, and preventing others from getting sick if an underlying illness is a cause.

People living with chronic conditions, such as IBD, IBS, or celiac disease, should follow their doctor’s recommendations on diet to help prevent making their symptoms worse.

Hydration

Diarrhea can lead to dehydration if a person does not replace the lost fluids. People with mild to moderate diarrhea may find the following methods to replace lost fluids helpful:

  • electrolyte-replacement solutions, such as Gatorade or Pedialyte
  • watered-down apple juice
  • ginger ale
  • soup broth

It is important to use fluids that contain sugar and salt to help replace lost electrolytes.

Foods to eat

Someone with acute diarrhea should eat bland foods until their stomach starts to feel better. Bananas, rice, soup, and crackers are particularly easy to digest and can help to harden stools.

Hand hygiene

Hand washing and other hygiene measures provide a crucial step in preventing the spread of the germs that cause diarrhea. According to the World Health Organization (WHO), hand washing with soap can help prevent diarrheal disease by up to 48%.

A person should frequently wash their hands with soap and water or an alcohol-based hand rub throughout the day, including:

  • after changing a diaper
  • before and after preparing food or eating
  • after going to the bathroom
  • after touching any infectious material

Medical treatment

Treatment of diarrhea, whether it is acute or chronic, depends on its cause.

If an infection is to blame, medication may help. However, sometimes a person just needs rest, fluids, and time.

As long as there is no fever or blood in the stools, a person can use over-the-counter (OTC) medications to reduce the frequency of loose stools. These will not cure the cause of diarrhea but can make someone feel better and cut down the fluid loss.

Medications include:

  • loperamide (Imodium)
  • diphenoxylate-atropine (Lomotil)
  • bismuth subsalicylate (Pepto-Bismol, Kaopectate)

If a specific food or substance, such as lactose or gluten, causes diarrhea, it is important for a person to avoid those triggers in the future.

When IBD or IBS causes diarrhea, a person may need to use medications to control the immune system or inflammatory reaction. These can include biologics and steroids. A person should follow their treatment plan when taking medications and tell their doctor if these no longer help.

Learn more about IBD treatments here.

People with diarrhea that do not see improvements with home measures or other treatments within 48 hours should see their doctor.

A person should seek medical attention immediately if they experience diarrhea and any of the following symptoms:

  • signs of dehydration, such as dry mouth, cramps, thirst, dark-colored urine, dizziness, not urinating, or confusion
  • signs of bleeding, such as bloody or black diarrhea, or stools that contain blood or mucus
  • a high temperature
  • severe stomach pain

A doctor will review a person’s medical history, do a physical exam, and may order additional diagnostic tests. Once the doctor finds the cause of the diarrhea, they can recommend an appropriate treatment.

Many kinds of diarrhea are preventable. Hand hygiene can help prevent acute illness, and avoiding trigger foods may help a person living with a chronic condition avoid flares.

Some additional prevention methods include:

  • Rotavirus vaccine: Rotavirus is a virus that causes diarrhea in young children. The CDC recommend vaccinating babies and young children to help prevent this viral infection.
  • Food preparation: A person should only consume well-cooked foods, drink purified water, particularly while traveling, and avoid eating contaminated food. This can help a person avoid food poisoning.

The following are answers to some frequently asked questions about the causes of diarrhea after eating.

What causes yellow diarrhea after eating?

Stool color can give some clues to a person’s health. While brown stool indicates the person is healthy, yellow stool could indicate the presence of Giardia, a common parasite. It can also indicate issues with the liver, gallbladder disease, or malnutrition associated with celiac disease. Black or red stools can indicate intestinal bleeding, while green, blue, or orange stools can result from eating foods containing these colors.

What causes stomach pain and diarrhea after eating?

Several conditions can cause stomach pain along with diarrhea. Some common ones include:

  • IBD
  • IBS
  • celiac disease
  • infections
  • food poisoning

What causes fatigue and diarrhea after eating?

People who experience both fatigue and diarrhea likely have an underlying health condition, such as celiac disease or IBD. It is also possible that a person has an acute stomach infection that is causing fatigue as well.

What causes diarrhea 6 hours after eating?

If a person experiences diarrhea within hours of eating, they may have food poisoning. Symptoms such as diarrhea can occur in as little as a few hours from eating the bad food. It is also possible that a person may have an undiagnosed case of IBS, so they should talk with their doctor if symptoms persist.

What causes diarrhea after eating salad?

Having a bowel movement or even diarrhea after eating a salad is not uncommon or concerning when no other symptoms are present. Salad and other foods high in fiber can often trigger a bowel movement and possibly even diarrhea since some people do not always digest it well. However, diarrhea after eating a salad could also indicate exposure to contamination from spoiled or improperly washed ingredients.

What causes gas and diarrhea after eating fatty foods?

In some cases, gas and diarrhea after eating fatty foods may be the result of a person consuming too much. Some underlying conditions, such as gallbladder disease or IBS, can also cause a combination of gas and diarrhea.

Can Covid cause diarrhea after eating?

Covid can cause gastrointestinal symptoms, including diarrhea. Symptoms typically clear within a few weeks, but they can sometimes last for months or years.

In most cases, acute diarrhea will pass through a person’s system within 2 days with or without treatment. During this time, they should stay hydrated and possibly take OTC medication for some symptom relief.

While chronic diarrhea may have a more distinct medical cause, such as IBD, the outlook is still good. Treatments, including avoiding certain foods and following a treatment plan, can help improve a person’s outcome.