Diarrhea After Eating - The Causes

Diarrhea after eating is extremely common. On average every person in the world has diarrhea about four times a year and some of us have it a lot more than that!

When we eat this stimulates the bowels into action and causes peristalsis to kick in. This is a wave like motion which pushes the stools along the gut towards their destination.

The feeling that we want to have a bowel movement after eating is normal although it should not happen after every meal. Having diarrhea however is not normal.

This problem can be caused by many different things and there is not one simple answer. Read on to find some of the many different reasons for having diarrhea after eating.

Diarrhea After Eating Anything

Diarrhea after eating anything is also known as postprandial diarrhea. If you regularly suffer from diarrhea which is triggered by eating and there does not seem to be a specific cause like one of the things below then you should ask to see a gastroenterologist to try and get a firm diagnosis.

Some people have diarrhea right after eating and for others it sets in a little later. When we eat out bowels are stimulated and the wave like action which pushes our feces along the bowel is triggered but we should not have diarrhea immediately after eating.

Constantly suffering from diarrhea every time you eat is very debilitating both in a physical and a psychological way. Eating is such a fundamental part of our lives that to suffer every time you do something so normal is very difficult to cope with.

Many doctors are apt to immediately put a label of irritable bowel syndrome on this type of problem especially if you have stomach pain and diarrhea after eating but there are other diagnoses which should be considered.

Of course you may have IBS-D or diarrhea predominant irritable bowel syndrome. Up to twenty percent of people in developed nations are living with irritable bowel syndrome and some do not even know it.  The pain, diarrhea and gas of IBS-D is commonly triggered by eating and then resolves after a bowel movement.

Sometimes IBS is misdiagnosed and your symptoms could be caused by other things. Other possible causes include:

  • Bile acid malabsorption - in BAM the bile fails to be re-absorbed as it should be which leads to diarrhea.
  • Celiac disease - an autoimmune disease where gluten must be avoided.
  • Pancreatic exocrine insufficiency - the pancreas produces enzymes which help digest food; amylase (carbohydrate), lipase (fat), protease (protein). When these are lacking or the levels are low food is not broken down properly and remains in the small intestine causing water to be drawn in, leading to diarrhea.
  • A deficiency of enzymes like sucrase, maltase, glucoamylase or isomaltase, found in the small intestine and needed to digest certain foods.

It is worth considering that one of these things could be causing your diarrhea. If you have an ongoing problem with diarrhea after eating then discuss the different possible diagnoses with your doctor.

Chronic diarrhea can be a sign of many different things and sometimes extensive tests are needed to find an answer.

Diarrhea After Eating Fish

Fish Allergy

There are two main reasons why you might have diarrhea after eating fish: allergy and poisoning, with a third, parasites gaining momentum.

Some people are allergic to certain fish species and their symptoms can include diarrhea alongside abdominal pain, headache, rashes, breathing problems, swelling and shock.

Allergy to finned fish is more common in cultures that eat lots of fish like in Scandinavia and some Asian countries.

If you suspect you have a fish allergy problem then it is important to get proper testing from an allergy specialist. Cross contamination can happen during food preparation so it is best to avoid eating in all seafood restaurants and to warn the staff in other restaurants about your problem.

Diarrhea After Eating Fish - Sushi

Unfortunately since the advent of DNA testing it has been found that in many countries fish fraud is on the rise.

This takes the form of species substitution where a cheaper fish is substituted for a more expensive one. This can be extremely dangerous for people with allergies as they could be unwittingly eating a species that they have been warned to avoid.

The highest rates of mislabeling have been found with snapper and tuna.

In the USA fish species are one of the foods that must appear on labels to help people with allergies but this cannot always be relied upon if fraud is happening. Sushi restaurants have been found to have the highest levels of mislabeled fish.

Fish Food Poisoning

Food poisoning from fish could be the cause of your diarrhea. The two main types of fish food poisoning are Ciguatera poisoning and Scombroid poisoning.

Ciguatera poisoning is caused by ciguatoxin which is found in algae and is eaten by small fish which are then eaten by bigger fish. These are mostly reef fish from tropical waters like amberjack, barracuda, grouper, red snapper, sea bass and Spanish mackerel. Symptoms include nausea, vomiting, diarrhea, muscle pains, dizziness, tingling and numbness.

Scombroid poisoning occurs when fish has not been refrigerated or frozen straight after being caught. Improper storage of the fish causes the build up of toxins, in particular histadine which breaks down into histamine in the body and causes a typical allergic like reaction with rashes, breathing problems, diarrhea, vomiting and generally feeling unwell.

The fish most often implicated are mackerel, tuna, albacore, sardines, anchovies and mahi-mahi but other fish that has not been stored properly can be to blame.

I have suffered with this type of poisoning myself after eating fish 'fresh from the boat'. Unfortunately the five hours it took on a hot summer's day to get home from the coast and eat the fish was enough to make me extremely ill!

You cannot protect yourself from fish poisoning by cooking the fish. If you are suffering from diarrhea and nausea or vomiting after eating fish then normally it will pass in 24-48 hours but it is important to drink plenty of fluids to prevent dehydration.

Seek medical attention quickly if an elderly person or a child is suspected of having fish poisoning or if you have breathing difficulties, tingling, numbness, swelling of the tongue, dizziness, a rapid heart beat or feel very unwell. 

Fish Parasite Infections

As the popularity of sushi has exploded around the world the number of people suffering from explosive diarrhea may have seen an upturn. The raw fish in sushi can be infected with parasites which can cause symptoms such as:

  • Diarrhea, often with blood and mucus (standard or explosive which is more common with parasite infections)
  • Nausea and vomiting
  • Extremely bad abdominal pain (often upper)
  • Abdominal distension
  • Bowel obstruction
  • Low grade fever
  • Rash and itching
  • Collapse

Although infection with parasites from sushi is not common and until recently 90% of cases were diagnosed in Japan, it is on the increase.

The most common parasite infection caught in this way is Anisakiasis. The Anisakis worm can burrow into the stomach wall and cause swelling, inflammation, pain and bleeding.

Other kinds of worms can also be caught from fresh and saltwater fish and although humans are not their natural habitat they can become accidental hosts!

Parasites can cause diarrhea after eating other raw fish dishes such as ceviche.

The main ways of killing fish parasites is through freezing or heating.

In theory eating sushi or ceviche using fish that has been previously frozen is safe but it is quite complicated because the temperatures needed to kill the different kinds of worm are very low and the time in the freezer ranges from 15 hours to 7 days depending on the freezer temperature. For more information see the FDA guidance here.

Do not eat raw or under-cooked fish if you are pregnant or your immune system is compromised. Sushi is perceived as being a very healthy food but not always!

Diarrhea After Eating Shellfish

Diarrhea After Eating Shellfish - Oysters

As with fish some people are allergic to shellfish however most people are allergic to one but not the other. Allergic reactions to shellfish normally come on very quickly and you should seek medical attention immediately.

Shellfish poisoning is caused when the shellfish feed on contaminated plankton or algae. If the shellfish is contaminated with bacteria like e-coli or viruses like norovirus then these can be killed by careful cooking but some other toxins are not affected by heat.

You are more likely to get shellfish poisoning if you gather the shellfish yourself as commercially grown shellfish are regularly monitored. Do not eat shellfish when traveling in developing countries and avoid them in the summer.

As with fish poisoning (see above) if you have worrying symptoms then get medical help. If you are suffering from diarrhea and vomiting then replace fluids often.

Diarrhea After Eating Bread and Pasta

Most bread and pasta is made from wheat and there seems to be an increasing problem with people having difficulty digesting wheat. There could be several reasons for this.

The general term which tends to be used for this problem is gluten intolerance but this can mean different things to different people.

Diarrhea After Eating Bread - Selection of Bread in Basket
  1. You could have undiagnosed celiac disease. Celiac disease is an autoimmune disease and these types of diseases are becoming increasingly common in our modern society, although nobody is exactly sure why. Eating gluten leads to an immune response where your own body attacks your small intestine causing damage. About one in every hundred people in the developed world are thought to suffer and it is very under-diagnosed. It is worth getting a test to exclude this. If positive, a gluten free diet must be followed for life.
  2. Some people do not have full blown celiac disease but nevertheless are sensitive to gluten. You can test this out under supervision from a registered dietitian by excluding gluten containing foods like wheat, barley and rye for a period of time and then reintroducing them to see if it makes any difference. If you see an effect then you could reduce your symptoms by eating gluten free bread and pasta.
  3. Some people do not have a sensitivity to gluten specifically but they find it hard to digest certain types of wheat products. Try eating toast, sourdough bread or bread from specialist bakeries. Some people seem to be extra sensitive to factory made bread because it is not made using traditional methods and it does not get a second rising which seems to make it harder to digest.
  4. Some people do suffer from a yeast intolerance but this is not nearly as common as you might think. A whole industry has grown up around treating 'yeast problems' which is not always warranted. However, a small number of people do have genuine problems. If you suspect that this may be you then I recommend you go and see an allergy specialist to get properly diagnosed. 

Diarrhea After Eating Chicken

Did you know that 88% of store bought fresh chickens in the US and 73% of chickens in the UK are contaminated with camplylobacter bacteria that causes food poisoning? A high percentage are also contaminated with salmonella. Both these bugs can cause serious gastroenteritis if the chickens are not prepared and cooked properly.

Other types of poultry like turkey, goose and guinea fowl are also a risk.

Symptoms can include diarrhea, nausea, vomiting, abdominal cramps, fever, chills and blood in the stools. The severity of the symptoms varies with some people only suffering mildly and others needing hospital treatment.

Roast Chicken

Chicken is one of the most popular meats on the planet and most of us like a roast chicken dinner or spicy chicken wings, so what can we do to protect ourselves?

  • Never wash chicken before cooking. This only spreads the germs around the kitchen, contaminating working areas and leaving the bugs to be picked up by the next food to be prepared.
  • Always use separate chopping boards for raw meat and wash them thoroughly afterwards with soap and very hot water.
  • Always wash your hands thoroughly after touching raw meat. I am often called into the kitchen to do something by my husband who needs help because he can't touch anything while he is preparing the chicken but I don't mind as I don't want to get ill!
  • Keep raw meat covered and in a separate section in the fridge.
  • Defrost chicken completely before cooking if it has been frozen.
  • Cook poultry for the recommended time to a temperature of 165F (74C) as measured by a thermometer in the thickest part of the bird. Yes this is one of those gadgets everybody should have.
  • Cook stuffing separately not inside the bird.
  • At the end of the cooking time make sure the juices run clear when skewered. If not cook some more.

I have suffered diarrhea from eating undercooked chicken in a restaurant and I was diagnosed with salmonella poisoning after having a stool sample analyzed. I suffered diarrhea and terrible abdominal cramps for over a month. I would not wish that on anyone!

If you have eaten chicken within the last week and you have the symptoms described above then you may have chicken food poisoning. If you are caring for someone elderly or a young child then ask for medical advice.

Drink plenty of fluids and if your symptoms do not subside in 48 hours you may need to get tested.

If you have diarrhea then do not go to a medical facility without talking to them first as you also have to think about protecting other people.

Diarrhea After Eating Eggs

Eggs are a very common food allergen. An allergy is when the body's immune system wrongly recognizes food such as the proteins in eggs as harmful and so will mount an attack. This causes symptoms which often include diarrhea and other gastro problems but also symptoms in other parts of the body like rashes, swelling and breathing difficulties.

Some people are only allergic to the white and some only to the yolk.

Egg intolerance can also cause diarrhea. A food intolerance is caused when your body has difficulty digesting something. This is usually due to the lack of, or low levels of an enzyme. Symptoms such as diarrhea, abdominal cramps and nausea will be confined to the gastrointestinal tract.


One reason eggs can easily be contaminated with bacteria like salmonella is because, although it sounds horrible, the chicken only has one hole for everything to come out of. It poops / pees and lays eggs through the same orifice. Sometimes however eggs become contaminated inside the chicken, before the shell is added.

Contaminated eggs can make you ill if they are undercooked. If you are pregnant or elderly or a child be especially careful to only eat well cooked eggs and do not eat foods containing raw eggs like mousse.

Be careful when handling egg shells as the outside of the egg may be contaminated. Dispose of uncooked shells carefully and wash your hands very well after handling raw eggs.

If you regularly feel ill and have diarrhea after eating eggs then make an appointment to see an allergist. If it is a one off thing then you have probably caught something and if you are not better in 48 hours after having plenty of fluids then see a doctor.

Diarrhea After Eating Cheese or Drinking Milk

Cheese on a Board

Cheese and milk seem so benign don't they? It seems hard to imagine having diarrhea after eating cheese or drinking milk but in fact 65% of the world's population have a reduced ability to digest certain types of cheese and other dairy products as they are lactose intolerant.

People of Northern European descent retain the enzyme lactase, which we use to digest the milk sugar lactose, into adulthood but most other people lose their lactase when they are weaned. 

People with lactose intolerance can usually have small amounts of lactose without having problems but the level of tolerance varies from person to person.

Hard cheeses and aged cheeses only have very low levels of lactose and it is normally the soft cheeses like cream cheese and mascarpone which are the problem causing culprits.

The fresher and younger a cheese is the more lactose it will have in it. Milk has the highest quantity of lactose. Other lactose containing foods include yoghurt, ice cream, cream and custard.

Another reason for having diarrhea after eating cheese is that some cheeses can harbor harmful levels of bacteria. This is more likely if they are unpasteurized and if they are soft. Listeria is the most common cause of this problem and can sometimes be found in certain cheeses especially brie, camembert, feta and ricotta.

Listeria poisoning attacks the nervous system and so causes symptoms like poor co-ordination, loss of balance, seizures and confusion as well as causing fever, diarrhea and vomiting.

The symptoms may not come on for up to eight weeks after eating the infected cheese.

If you have any of the above symptoms then seek help immediately. Soft mould-ripened cheeses like brie, camembert, roquefort, goat and danish blue are not safe to eat if you are pregnant.

Diarrhea After Eating Sugar Free Foods

Sugar Free Gum

Some foods labelled as sugar free contain artificial sweeteners which have a laxative effect. They can usually be tolerated in small amounts but if you overdo it you will end up with diarrhea.

It is a good idea to read labels carefully so that you know if you are coming into contact with these sweeteners.

The two which cause the most problems are mannitol and sorbitol. The FDA requires any products with levels that may cause diarrhea to warn purchasers on the label. Some people also react to maltitol and xylitol.

 Sorbitol diarrhea is quite common in people who eat a lot of sugar free chocolate, hard candy, jams, jellies and other products. Children are particularly susceptible. Some people even use these products deliberately to treat their constipation but most people do not want to end up with sugar free gum diarrhea!

These sweeteners are fodmaps. For a list of other high fodmap containing foods that can cause diarrhea, pain and bloating and information about following a low fodmap diet please see the page Fodmap Diet - Banish Pain and Bloating.

Diarrhea After Eating Spicy Foods

Many of us love to eat food spiced with chili or other hot spices but some of us suffer the consequences. You may be wondering why some people can get away with eating hot wings, curries and chili con carne and other people suffer from diarrhea, pain or heartburn.

To a certain extent it is about what you are used to. If you only eat spicy food once in a blue moon then your body gets a bit of a surprise and your bowels are more likely to complain.

Chili peppers

It has been found that you build up a tolerance to spicy food if you eat it regularly. This has certainly happened to me and I can now happily eat levels of chili that I would not have even thought about when I was younger.

So, to improve your tolerance try having small amounts and then increasing the quantity that you eat gradually.

However, do be aware that studies have shown that if you have an underlying bowel problem like irritable bowel syndrome for example you are more likely to suffer if you eat hot spices.

It may be worth asking for some checks to make sure that your bowels are normal.

Just think though what it would feel like if you got chili in your eye. Ouch! The lining of the intestines can be irritated by spices in the same way and unfortunately you may just have to settle for something a bit more soothing.

Diarrhea After Eating Out

Of course when you eat out you cannot control the way the fridge is organized and you don't know if the restaurant staff have washed their hands.

You are trusting that the place where you are eating will keep you safe but unfortunately we have all at one time or another ended up with diarrhea after what should have been an enjoyable night out.

Many countries and states have systems in place to check on the food hygiene standards in their restaurants. If a rating system exists where you live then take advantage of it.

We are lucky in the UK because we have a national inspection system called 'The Scores on the Doors'. Personally I would not walk through the door of any restaurant unless it scored 4/5 or 5/5. Hey some of those kebab, shawarma and chicken restaurants are great but not all of them!

If you do suffer from diarrhea after eating out and you think it might be linked to practices in the restaurant (other people are also ill) then report your worries to the authorities so that they can investigate and prevent it happening to anybody else.

Be very careful if you are traveling in the developing world as food hygiene standards are not always as high as they should be. Street food can be delicious but sometimes there is pay back!

Some people regularly suffer diarrhea after eating out but never at home. This can be a bit of a mystery but it could be that you are sensitive to ingredients the restaurants are using that you would never use at home. One example would be MSG that is often used in Chinese restaurants.

Another cause of diarrhea after eating could be the quantity of food eaten. We do tend to eat more food when we go out and eating large quantities of food can stimulate your bowels to run faster than normal especially if you suffer from irritable bowel syndrome.

You may have heard of the brain/gut axis. A communication system exists between the brain and the gut with nerves sending messages up and down both ways all the time.

In some people these nerve connections are extra sensitive and thoughts and feelings that provoke anxiety can cause an exaggerated gut response and lead to diarrhea. It may be a stretch to suggest that some people are so anxious about eating out that they experience diarrhea but in fact this could happen. 

Lastly many people tend to drink more alcohol when they are out and this is a well known trigger for diarrhea. See Diarrhea After Drinking for more information.

What Shall I Do If I Have Diarrhea After Eating?

As you can see there are many different reasons for having diarrhea after eating and in most cases it will be a one off thing and you should recover in a few days. Make sure that you drink plenty to avoid suffering from dehydration.

If you find that you are suffering regularly then you will have to do some detective work.

Keeping a food diary is a good idea to see if any particular foods are triggering your diarrhea. Some people do have food intolerances and it can be helpful to eat a limited range of foods for a while and then re-introduce foods one at a time to see if you get a reaction.

The difficulty is that unlike full blown allergies the symptoms from a food intolerance often do not show up for several hours or even days.

Elimination diets can be dangerous if too many foods are cut out or for too long a period of time. It is best to do this under the supervision of a qualified dietitian.

To get a proper diagnosis for your diarrhea after eating it may be necessary to see a specialist in gastrointestinal problems but this is important as without knowing the cause of the problem it is difficult to know the way forward to a diarrhea free existence.

I was diagnosed with irritable bowel syndrome many years ago and would regularly have diarrhea after eating. Eventually I found the answer to my problem and can now eat without worrying.

For more information about this please see the page 21 IBS Treatment Options.

DiarrheaNurse hopes that you have found some answers to your questions about diarrhea after eating from reading this page.

For more information about causes of diarrhea and chronic diarrhea causes please browse the site. 

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Photo attribution:

Gum by Seo75 https://commons.wikimedia.org/wiki/File:Eclipse-Ice-gum-lemonburst-peppermint-and-spearmint-flavours.JPG

Chicken (cropped) by Marjon Lazarevski https://www.flickr.com/photos/mlazarevski/8500053523

Eggs (cropped) by SG https://www.flickr.com/photos/13891558@N00/3361165559

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