Most of us may expect some indigestion after a heavy meal but for some people there is the need to have a bowel movement after eating. This may occur immediately after eating or a short while thereafter. In some cases where this the urging to pass stool occurs with every meal and after eating any time of food, it has to be considered as a symptom of some underlying problem.
It is not entirely uncommon to have a bowel movement after eating. If a person has not a bowel movement at their usual time then there are several reasons why a meal can trigger the urge to pass stool. This is not considered to be abnormal or a symptom of some disease. In fact even if a person did have a regular bowel movement, there is still the possibility of a meal triggering a bowel movement particularly if a person overeats.
Read more on diarrhea with overeating.
Why the need to have a bowel movement after a meal?
A bowel movement is a result of the colon being stretched with stool. This stretching triggers strong contractions and stool is pushed into the rectum. The urging to pass stool becomes stronger and eventually if the situation is appropriate, the anal sphincters contract. The colonic contractions then push the the stool out through the anus and into the environment.
To understand why this bowel movement process is triggered by eating in the absense of any disease, it is important to first understand defecation reflexes. There are many types of reflexes in the body. These are pathways where stimulation of nerves triggers impulses in other nerves without the brain having to process the incoming signals and then emitting outgoing signals.
Read more on defecation reflexes.
With defecation reflexes, stimuli in one part of the gut can trigger actions in another part of the gut. Among the different defecation reflexes, two of these reflexes are more likely to be involved with a bowel movement after eating. These reflexes receive signals from stretching of the upper gut and causes mass movements within the colon, thereby hastening the need to have a bowel movement.
- Gastrocolic reflex is stimulated by the stretching of the stomach wall which occurs with eating food. It then triggers mass movements in the colon.
- Duodenocolic reflex is stimulated by the stretching of the duodenal wall which occurs as food from the stomach is passed into the first part of the small intestine known as the duodenum. It also triggers mass movements in the colon.
There are times where these reflexes as well as the other defecation reflexes are hyperreactive. Similarly irritation of the gut can also cause disturbances in bowel habit that may lead to a bowel movement or diarrhea after eating.
Read more on diarrhea after eating.
Causes of Bowel Movement After Eating
These are some of the possible causes of the need to have a bowel movement after eating, apart from overeating which can cause the need to pass stool.
Stimulants and Irritants
A number of substances may stimulate a bowel movement either due to the excitatory action of the substance or due to irritation to the bowels.
For example, caffeine is a well known stimulant found in beverages like coffee and cola which can stimulate a bowel movement. Depending on individual sensity, some people may react to even a small amount of caffeine. The same applies to nicotine, a common stimulant found in tobacco.
Spicy foods and alcohol can irritate the gut lining and trigger a bowel movement. Similar to caffeine and nicotine, the bowel movement may be triggered by varying quantities of these substances, depending on how sensitive a person is to these substances. Some preservatives and food additives may also be irritants.
Gastroenteritis and Enterocolitis
Gastroenteritis and enterocolitis are common inflammatory conditions of the stomach and bowels. It is also a common cause of acute diarrhea with most cases being due to infections, particularly viral infections. This often occurs as outbreaks such as the rotavirus diarrhea that affects children in day care and kindergarten. Bacteria and protozoa may also be responsible. Sometimes the toxins of these microbes may contaminate food and water as is the case with food poisoning.
Food Intolerance and Malabsorption
A number of foods can trigger a gastrointestinal upset and even a bowel movement or diarrhea if it is not properly digested and absorbed. In lactose intolerance for example, the body’s lack of the enzyme known as lactase means that milk sugar (lactose) cannot be digested. Similarly in fructose malabsorption the body’s inability to digest and absorb fructose means that remnants remain in the gut. This causes a host of gastrointestinal symptoms such as nausea, abdominal cramps and diarrhea.
Irritable Bowel Syndrome
Irritable bowel syndrome (IBS) is a common functional bowel disorder that results in abdominal pain and other symptoms like very frequent or infrequent bowel movements. People who suffer with IBS-D (irritable bowel syndrome with diarrhea) may experience the need to have a bowel movement after eating, even if it is not diarrheal stool. This can persist even when there is no obvious flareup.
In gallbladder or bile duct disease where bile outflow is affected, diarrhea can occur a short while after eating a meal. This is more likely to occur after eating a fatty meal. Bile is responsible for emulsifying fats in the small intestine. This allows for the digestive enzymes to break down the fats further. However, without bile the fats may pass through the bowel and exist with stool. It can give rise to greasy stools known as steatorrhea.
Dumping syndrome is where the movement through the upper gut is very fast. This arises when a portion of the stomach or even all of the stomach has been surgically removed. It is more frequently seen with certain types of weight loss surgery. The transit time is not necessarily the reason why diarrhea may occur a while after eating. Rather it is the undigested food that can draw out water into the bowels and result in watery diarrhea.
- Exercise (vigrous physical activity after a meal)
- Inflammatory bowel disease (IBD)