Diarrhea after eating is a symptom of several disorders affecting the bowel. There is a misconception that the stool is actually the food that was consumed in the last meal but this is not possible. It takes food that is eaten between 24 to 72 hours. Even in cases of diarrhea, the movement is much more rapid but not instantaneous in humans. Diarrhea immediately after eating is actually a consequence of bowel irritation and prematurely triggered defecation reflexes. It can occur anywhere within seconds after completing a meal to minutes thereafter. Sometimes a person has an intense urge to pass stool while eating.
The bowel has two supplies of nerves. A network of nerves that run between different parts of the bowel and sometimes extend to the spinal cord. The other is the nerves carrying signals to and from the brain. Defecation reflexes are like an automated system that :
- Fills the rectum with stool
- Elicits the urge to pass stool
- Allows for the anal sphincter to relax to pass stool
- Push out the stool in the lower bowel
There are some reflexes which are stimulated higher up the bowels. For example, the gastrocolic reflex increases bowel motility in the colon when the stomach stretches from eating food.
When the lining of the bowel (wall of the gut) is irritated or inflamed, it is hyperreactive. Bowel transit time is reduced as the bowel walls push through the contents much faster than normal. These movements are known as peristalsis and occur as waves throughout the bowel wall. Peristalsis commences as high up as the esophagus and extends all the way to the rectum. In some bowel disorders eating and the peristaltic waves associated with it can actually exacerbate the movements throughout the bowel even though the food has not reached the lower parts of the gut as yet. This can force out stool.
Diarrhea vs Normal Stool
While it is not entirely abnormal to have an urge to pass stool after eating, it is usually an urge that can be controlled and the stool is not of diarrhea consistency. It also does not occur after every single meal. Diarrhea in the strict definition is more than 3 bowel movements in a day, passing of very loose or watery stool that exceeds 200g or 200ml in weight or volume respectively. Diarrhea the stool indicates a problem in the bowel – either the bowel wall is irritated, water is not being reabsorbed from the bowel or excessive water is being pushed into the gut, or movement through the bowel is abnormally rapid.
Diarrhea immediately after eating can occur with just about any bowel disease where diarrhea is a symptoms. However, it is more likely in a person suffering from :
- Irritable bowel syndrome (IBS) and more specifically the diarrhea-predominant variety. IBS is a functional bowel disorder where the exact cause is unknown and there is no underlying disease process.
- Food poisoning where the lining of the gut is irritated after exposure to toxins in foods. These toxins may be produced by microbes like bacteria, are naturally occurring poisons within certain foods, are artificial irritants that have contaminated food and water.
- Gastroenteritis is the irritation of the stomach, small and large intestine most commonly caused by a viral infection. It is commonly referred to as the ‘stomach flu’ or ‘tummy bug’. It is self limiting and resolves quickly.
- Inflammatory bowel disease (IBD) is a chronic disease where the bowel walls are inflamed, secreted excessive mucus, may become ulcerated and lead to bleeding. It is usually during the acute episodes when diarrhea immediately after eating is seen.
There are various other possible causes of diarrhea immediately after eating. Even anxiety can lead to this symptom. Food intolerance, allergies and malabsorption of certain substances are another possible cause but diarrhea is only worse hours after eating, and if triggered by meals, it is usually related to specific foods like dairy. Explosive diarrhea after eating are associated with acute causes like food poisoning and gastroenteritis.