Are you experiencing diarrhoea but not sure what’s causing it? This article will help you to understand possible causes of diarrhoea, such as chronic conditions including irritable bowel syndrome (IBS), inflammatory bowel disease (IBD) and coeliac disease, or acute causes like antibiotic use or gastroenteritis.
Understanding the causes of diarrhoea after eating will help you know how to manage and prevent it, and help you know when medical investigations are warranted.
This article is not individual personalised medical advice and you should discuss concerns of diarrhoea after eating with your Doctor.
Chronic conditions that cause diarrhoea after eating
If your diarrhoea is lasting for more than four weeks – this is chronic diarrhoea. This section will briefly discuss some common causes of chronic diarrhoea, all of which should be considered for investigation by your doctor.
Functional gut disorders such as irritable bowel syndrome
A functional gut disorder (FGD) is when there are gut symptoms present without there being any structural abnormality or damage in the gut that is causing them.
IBS is a common FGD and is prevalent in 10-20% of the population. If you have stools that are on the looser side for more than 25% of the time, your IBS is classed as IBS-Diarrhoea (IBS-D).
The British Society of Gastroenterology defines IBS as disordered communication between the gut and the brain (known as the gut-brain axis). The gut and the brain are always communicating with one another via their own nervous systems. You may have heard of the gut being your second brain for this exact reason. When this communication is disrupted, this can result in IBS symptoms, including diarrhoea after eating.
Stress and anxiety can disrupt the gut-brain axis and are therefore linked with an increased risk of IBS. Certain foods are also known to trigger diarrhoea after eating in IBS, which will be discussed in further detail later on in this article.
Post-infectious IBS
Infectious gastroenteritis, which may be caused by food poisoning or a virus, can result in diarrhoea which usually lasts less than a week. However, infectious gastroenteritis can increase your risk of IBS by 4 fold.
If your chronic diarrhoea or IBS-D started following a bout of infectious gastroenteritis, you may have post-infectious IBS.
Bile acid malabsorption
Approximately one-third of people diagnosed with IBS-D have been found to have bile acid malabsorption (BAM). BAM is when you do not reabsorb your bile salts efficiently in your small bowel. When the bile salts reach the colon, water is drawn in resulting in diarrhoea and other gut symptoms.
The main symptom of BAM is often urgent, watery diarrhoea after eating, which can often be green or yellow. BAM is diagnosed using a SeHCAT scan and should be managed with medication prescribed by your registered healthcare professional.
Inflammatory bowel disease
Crohn’s disease and ulcerative colitis are the main types of IBD, which both cause chronic inflammation in the gut. In IBD, diarrhoea may be bloody or mucusy, and present with other ‘red flag symptoms’ such as weight loss and anaemia.
A faecal calprotectin test is a stool sample test that can measure the amount of inflammation in your gut. It is one of the first routine tests you should have done if you have chronic diarrhoea.
If you have IBD and diarrhoea after eating, you should speak with your specialist IBD for advice and a management plan.
Pancreatic enzyme insufficiency (PEI)
PEI is a condition when you do not have an adequate amount of working pancreatic enzymes to break down the food in your small bowel. PEI causes weight loss, despite a normal dietary intake, loose stools, which may appear fatty or oily and be difficult to flush, foul-smelling flatulence and many other gut symptoms.
PEI is diagnosed with a test called a faecal elastase test and should be completed by your doctor if you have chronic diarrhoea.
Coeliac disease
Coeliac disease is a genetic autoimmune condition. In coeliac disease, the immune system attacks the cells of the small intestine when eating a gluten-containing diet. This unfortunately causes chronic inflammation and damages the lining of the small bowel. The result of this is chronic diarrhoea, weight loss and nutritional deficiencies due to malabsorption.
You can be tested for coeliac disease using a blood test, which again should be considered by your doctor if you have chronic gut symptoms and/or diarrhoea.
There is no cure for coeliac disease, however, it can be managed by following a strict gluten-free diet. This will help the small bowel heal and prevent long-term complications such as osteoporosis and increased risk of bowel cancer.
Causes of acute diarrhoea after eating
Acute diarrhoea is short-term diarrhoea and may be caused by food intolerances, antibiotics, gastroenteritis and the gastro-colic reflex.
Food intolerance
Food intolerances will typically cause diarrhoea after eating, with the most common food intolerance being lactose intolerance.
Lactose intolerance is the result of a lack of or insufficient amounts of the enzyme lactase, which is required to break down lactose. When lactose remains in the gut intact, it results in malabsorption symptoms including diarrhoea, abdominal bloating and cramping. Lactose intolerance may be short-term, for example, it may temporarily occur during a bout of gastroenteritis.
Fructose intolerance is another food intolerance that can cause diarrhoea after eating. Fructose is found in fruits such as mangos, pears and honey. We can only absorb so much fructose, and some people may absorb less than others. The fructose that is not absorbed can draw water into the bowel, resulting in diarrhoea. It is also fermented by gut bacteria in the colon, resulting in gas production (bloating and flatulence).
The best way to test and manage diarrhoea that is caused by a food intolerance is to trial a period of time (e.g. 2-4 weeks) restricting that food. After this time, it is important to reintroduce the food back into your diet in a small amount to test your tolerance. Start with a small portion size of the food and increase if you can tolerate it.
Note: Commercial food intolerance tests are unfortunately not scientifically valid and will not provide you with true results – so please do not waste your money!
Antibiotics
Many antibiotics can cause acute diarrhoea which may be due to the antibiotics disrupting the composition and function of the gut microbiota.
Some probiotics have been shown to prevent antibiotic-associated diarrhoea. Examples of probiotics that you can try to prevent antibiotic-associated diarrhoea are Optibac For Those on Antibiotics and Actimel.
Gastroenteritis
As described earlier, gastroenteritis can cause acute diarrhoea due to inflammation in the gut, which will often last less than a week.
During this time, your tolerance to certain foods or drinks, such as high-fibre foods and caffeine, may be reduced. You may also become temporarily intolerant to lactose if there is inflammation in the small bowel intestine, as this is where the enzyme lactase (that breaks down lactose) is made.
Gastro-colic reflex
The gastro-colic reflex refers to the reflex that controls the motility of the colon following the intake of a meal. It is the reason that many people feel an urge to open their bowels after a meal. Some people have a stronger gastro-colic reflex. When this happens, the stool in the colon is pushed through at a much faster rate which can cause diarrhoea after eating.
Smaller portion sizes and meals lower in fat may help reduce diarrhoea that is caused by a stronger gastro-colic reflex.
Which foods cause diarrhoea after eating?
Fatty foods
As previously mentioned, fat may increase the gastro-colic reflex and therefore the motility of the colon. This faster gut transit time could result in diarrhoea after eating. Foods high in fat can also cause more abdominal bloating after eating foods high in fat.
If you have a high fat intake, it is recommended that you try to reduce fat in your diet and monitor your symptoms. This includes fats from both typically healthy food, such as olive oil and oily fish, and saturated foods, such as sausages and beef burgers.
Spicy foods
Capsaicin, the active ingredient in chilli, can increase gut transit time and therefore may cause loose stools in some people.
People with IBS have been found to have more capsaicin receptors in the gut. This may explain why people with IBS get diarrhoea after eating chilli, alongside other symptoms such as abdominal pain.
Caffeine
Caffeine consumption has been shown to increase levels of the stress hormone cortisol. This means that caffeine may worsen stress and anxiety, and therefore diarrhoea, due to the gut-brain axis.
An increase in the motility of the colon has been seen following the consumption of caffeine. Therefore, if you have a high caffeine intake you may want to try a reduction and monitor your symptoms.
Alcohol
Chronic alcohol consumption can result in diarrhoea after eating, as alcohol may impair muscle movement in the small and large intestines.
However, this is seen in people who have excessive intake of alcohol. In short-term alcohol consumption, you may become constipated due to becoming dehydrated.
FODMAPs
FODMAPs are a type of fermentable carbohydrate found in many different foods. FODMAP stands for fermentable oligosaccharides, disaccharides, monosaccharides and polyols.
FODMAPs (except lactose in people with sufficient lactase enzymes) are not broken down in the small bowel like other foods are. In people with IBS or more sensitive guts, FODMAPs draw in water into the small bowel via a process called osmosis – with the result being osmotic (watery) diarrhoea. This has been demonstrated using studies where researchers gave participants fructose and measured the presence of water in the bowel using MRI studies.
FODMAPs pass through into the colon and are broken down by our gut microbes via a process called fermentation.
Lactose, fructose and polyols (mannitol and sorbitol) are FODMAPs that commonly cause diarrhoea in IBS. Foods that contain mannitol include cauliflower and celery, and foods that contain sorbitol include avocado and coconut.
How quickly does diarrhoea after eating happen?
The time it takes for the diarrhoea to start after eating will depend on the cause. For example, if the diarrhoea is due to the gastro-colic reflex, then it may occur immediately after eating a meal. Alternatively, if the diarrhoea is due to FODMAPs then this may take longer. This will vary from person to person due to differences in people’s gut transit time and their tolerance to that food.
Additionally, a sudden increase in intake of FODMAPs and fibre may trigger diarrhoea. If your usual intake of fibre is low, it is best to gradually increase your intake over a few weeks.
Can stress impact diarrhoea after eating?
Yes, stress can result in diarrhoea after eating due to interactions of the gut-brain axis. You may have a super busy lifestyle, back-to-back exams, stress at work, or perhaps anxiety caused by eating out without knowing where the nearest toilet is.
During periods of stress and anxiety, your tolerance to certain foods, such as the ones listed above, can be reduced. This increases the likelihood that they will cause diarrhoea.
However, for some people, diet may not play a part in this at all, and stress alone can have a direct impact on the gut by triggering gut symptoms via messenger signals between the gut-brain axis. If this is the case for you, keep reading on for tips on how to target the gut-brain axis to manage your diarrhoea.
The influence of stress on the gut-brain axis and its effect on gut symptoms is discussed in more detail in our post “Are Your Gut Issues Actually Caused by Stress?”.
