Diarrhea after eating is a symptom of several disorders affecting the bowel. There is a misconception that this 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 may occur with 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 or immediately after a meal but does not need to defecate.
Reasons for Urging After Meals
It is not uncommon to defecate after a meal like breakfast is that is a person’s bowel habit. This may also be time related. However, if the need to pass stool occurs after every or any meal then it needs to be investigated further. Not all causes of diarrhea immediately after eating is a serious disease or disorder.
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 hyper-reactive. 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.
Read more on sensitive stomach.
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. However, with certain diarrheal illnesses a person may pass watery stool after eating while in other cases the stool is firm, soft and well formed.
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.
Causes of Diarrhea After Eating
Diarrhea immediately after eating can occur with just about any bowel disease where diarrhea is a symptom. Often these conditions are acute. However, not all people who experience this symptom has a diarrheal illness. Some of these conditions may even be chronic and a part of daily life for many people. This can be inconvenient and even debilitating as a person is not unable to eat a meal without being close to a toilet.
Irritable bowel syndrome
Irritable bowel syndrome (IBS) and more specifically the diarrhea-predominant variety is a common reason for diarrhea after eating a meal. IBS is a functional bowel disorder where the exact cause is unknown and there is no underlying disease process. In diarrhea-predominant IBS, the movement through the bowels is fast than normal.
Food poisoning is where the lining of the gut is irritated and inflamed 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. The inflammation from these toxins may affect any part of the gut but usually affects the intestines.
Gastroenteritis is 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’. Bacteria and protozoa may also cause gastroenteritis. It is self limiting and usually resolves quickly. Gastroenteritis tends to be more common among children and spread quickly among them.
Inflammatory bowel disease
Inflammatory bowel disease (IBD) is a chronic disease where the bowel walls are inflamed and may become ulcerated. IBD is a chronic bowel disease with acute episodes arising every now and then. It is usually during the acute episodes when diarrhea immediately after eating is seen. This is more likely to occur with ulcerative colitis.
Food intolerance is where the body cannot digest and sometimes absorb certain nutrients. The most common is lactose intolerance where the body cannot digest milk sugar (lactose) due to a lack of the enzyme lactase. The undigested food in the bowels often leads to diarrhea. There are various other food intolerances although less common. It may include an intolerance to foods like gluten, sorbitol or fructose among other foods.
It is not uncommon to have unusual bowel-related symptoms with anxiety and psychological stress. Diarrhea after eating may be one such symptom. While it is more likely to occur in people with conditions like IBS or IBD, the effects of psychological stress can affect any person. Diarrhea after eating may even occur as one off episode and never occur again.
Weight Loss Surgery
Certain types of weight loss surgery, like a gastric bypass, may also be the cause of diarrhea after eating. It is more likely to occur with consuming certain foods or attempting to overeat. In these cases the diarrhea after meals can be avoided by controlling portion sizes and being selective with foods. This is known as dumping syndrome.