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Diarrhea After Eating: Why Does It Happen?

Having diarrhea after eating, or postprandial diarrhea (PD), can be a very uncomfortable experience. Let’s talk more about what causes diarrhea after eating and what you can do to relieve it.

Diarrhea is defined as having watery, loose stool three or more times per day. There are many different conditions that can cause diarrhea, including viral or bacterial infections, chronic health conditions, and even certain medications.

Diarrhea immediately after eating is called postprandial diarrhea, or PD. This type of diarrhea can be very inconvenient since it can cause an unexpected, strong urge to defecate right after eating. PD is usually a symptom of an underlying medical condition.

It’s very important to diagnose the underlying condition for PD. In some cases, it can be quite difficult to get an accurate diagnosis.

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A short bout of diarrhea after eating is categorized as acute diarrhea. If your diarrhea lasts more than four weeks, it’s chronic.

Common causes behind postprandial diarrhea include:

Acute gastroenteritis

Gastroenteritis, commonly known as the “stomach flu” or a “stomach bug” can be caused by different pathogens. It’s usually caused by viruses, such as rotavirus, norovirus, and enterovirus, but it can also be caused by bacteria. Gastroenteritis causes inflammation and irritation of the gastrointestinal mucosa. 

Gastroenteritis makes your digestive system very sensitive to irritative foods. Consuming these foods during a bout of gastroenteritis could lead to stomach pain and diarrhea after eating. Other symptoms include:

  • Abdominal cramps
  • Fever
  • Nausea and vomiting
  • Headache
  • Loss of appetite

Food poisoning

Food poisoning or foodborne illness occurs when we consume food or drinks that are contaminated with bacteria, viruses, or parasites. Toxic substances and chemicals can also cause food contamination.

Symptoms can start within a few hours or days of consuming contaminated food and include:

  • Diarrhea with or without blood
  • Nausea and vomiting
  • Abdominal pain or cramps
  • Fever

Lactose intolerance

Lactose intolerance occurs when your body can’t properly digest lactose, which is a sugar present in milk. This is usually caused by a deficiency of lactase, an enzyme that is responsible for digesting lactose. In babies and children, it’s important to differentiate between a milk allergy and lactose intolerance.

Lactose intolerance causes symptoms after ingesting dairy products, which may vary depending on the amount of dairy consumed and the severity of your lactase deficiency. Common symptoms include:

  • Bloating
  • Abdominal cramping or pain
  • Postprandial diarrhea
  • Flatulence

Sugar malabsorption

Sugar malabsorption is an inability to digest sugars like fructose and sorbitol. A different condition, called hereditary fructose intolerance (HFI), can cause life-threatening symptoms.

Fructose can increase the amount of water that is released to the bowels causing watery stool and other digestive symptoms. Many foods contain sugars that are poorly absorbed and digested, including:

  • Berries
  • Beans
  • Eggplant
  • Pumpkin
  • Onions
  • Garlic

These sugars may trigger symptoms in patients with an underlying condition — such as functional diarrhea or IBS — but they can also affect healthy individuals when eaten in large quantities.

Food allergies or intolerance

Allergies happen when your body has an exaggerated immune reaction to a substance. Humans can be allergic to any food. Common products causing food allergies include:

  • Shellfish
  • Nuts
  • Eggs
  • Fish
  • Milk
  • Wheat
  • Soy

Allergies can range from mild to severe, and they can also cause some other systemic symptoms, except for diarrhea after eating: 

  • Skin rashes
  • Wheezing
  • Difficulty breathing
  • Coughing
  • Itchy throat
  • Red, swollen eyes
  • Nasal congestion
  • Sneezing

These symptoms could be indicative of anaphylactic shock, which requires immediate medical assistance.

Irritable bowel syndrome (IBS)

A patient might be diagnosed with functional diarrhea or IBS with diarrhea (IBS-D) if no clear organic cause for the diarrhea can be identified. The main difference between these diagnoses is that IBS-D is usually accompanied by abdominal pain, whereas functional diarrhea isn’t. 

Either diarrhea or constipation can be predominant symptoms for IBS, but some patients alternate between experiencing either symptom.

Bile acid malabsorption (BAM)

Bile acids are produced in the liver and help digest fat. They enter the bowel and should be reabsorbed there, but in patients with BAM, this doesn’t happen. The resulting excessive amount of bile acids in the bowels leads to urgent diarrhea and bloating.

Testing for this condition is difficult, and it’s often misdiagnosed as IBS.

Celiac disease

When a patient with this autoimmune disease consumes gluten — a protein found in wheat, barley, and rye — their immune system causes damage to their small intestine.

This results in foul-smelling diarrhea, flatulence, abdominal pain, and other symptoms.

Exocrine pancreatic insufficiency (EPI)

The pancreas normally produces several enzymes that help digest food. With exocrine pancreatic insufficiency, there is a shortage of these enzymes, and food isn’t digested properly. This condition is usually caused by other pancreatic disorders, such as pancreatitis or diabetes, or conditions like celiac disease and cystic fibrosis.

Dumping syndrome

Dumping syndrome, or rapid gastric emptying, occurs when the stomach empties food into the small intestine faster than normal. It usually develops after gastric or esophageal surgery. 

Symptoms develop because the small intestine isn’t able to absorb nutrients from poorly-digested food. Symptoms are more common after a high-sugar meal, and they can begin 30 minutes after eating (early dumping syndrome) or 2–3 hours after a meal (late dumping syndrome). In addition to diarrhea after eating, symptoms can include:

  • Nausea
  • Abdominal cramping
  • Weakness
  • Dizziness
  • Sweating

Establishing the underlying cause of PD is the first step in treating it. Depending on the diagnosis, a doctor will prescribe different treatments and lifestyle modifications. Never self-medicate when you have persistent diarrhea. 

Try eating smaller, more frequent meals rather than large meals. Avoid foods that can irritate your digestive tract, such as fatty and spicy foods. Follow food safety measures and avoid handling other people’s food while you have PD.

Diarrhea can quickly lead to dehydration, so you’ll need to drink plenty of fluids and electrolytes while you’re ill. 

Food elimination diets are sometimes used to determine which foods cause adverse reactions.

Consider seeking medical attention if you have persistent or recurrent postprandial diarrhea, or if your diarrhea is associated with other symptoms, such as:

  • Bloody stools
  • Decreased urinary output
  • Dry skin
  • Fever
  • Sunken eyes
  • Severe or persistent abdominal pain
  • Loss of appetite
  • Weight loss
  • Skin pallor
  • Severe nausea

Maintain good hygiene to prevent diarrhea. Hygienic measures include everything from washing your hands frequently to drinking only clean water.

Make sure you wash all fruits and vegetables and cook your food properly, especially poultry, meat, pork, eggs, fish, and shellfish. Remember to check the expiration date on products before consuming them.

If you have chronic PD, visit your gastroenterologist for checkups. Don’t suspend your prescribed medications without first consulting a professional.

Postprandial diarrhea can leave you wondering, “Why do I have to poop right after I eat?”

Once the cause of your PD has been identified, it’s very important to take any prescribed medications, make sure you stay hydrated, follow food hygiene measures, and avoid foods that can trigger diarrhea after every meal.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6316316/

https://www.ncbi.nlm.nih.gov/pubmed/8249972

https://www.ncbi.nlm.nih.gov/pubmed/22624684

https://www.nhsinform.scot/illnesses-and-conditions/stomach-liver-and-gastrointestinal-tract/gastroenteritis

https://www.niddk.nih.gov/health-information/digestive-diseases/viral-gastroenteritis/treatment

https://www.mayoclinic.org/diseases-conditions/food-poisoning/symptoms-causes/syc-20356230

https://www.health.harvard.edu/diseases-and-conditions/soothing-solutions-for-irritable-bowel-syndrome

https://heas.health.vic.gov.au/early-childhood-services/allergy-and-intolerance/food-intolerance

https://emedicine.medscape.com/article/192761-overview

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