Which foods trigger irritable bowel syndrome?

Irritable bowel syndrome (IBS) is a common condition that affects the digestive system. It causes symptoms such as:

• stomach cramps

• bloating

• diarrhoea

• constipation

Symptoms can come and go and last for days or months.

The exact cause of IBS is unknown. It has been linked to things like food passing through your gut too quickly or too slowly, sensitive nerves in your gut, stress, and a family history of the condition. Although there's no cure, knowing which foods may cause symptoms can help you create a diet that works for you.

Julie Thompson, information manager at Guts UK, explains that foods which trigger a flare-up of symptoms vary from person-to-person, but there are some common themes.

Which foods can trigger IBS symptoms

Coffee

Many people reach for a coffee first thing in the morning, but caffeine - found in coffee, tea, cola, and chocolate - can lead to diarrhoea, especially if you have a more sensitive gut.

Caffeine is a gastrointestinal stimulant which means that it speeds up peristalsis, the muscle contractions that move food through the digestive tract. Both caffeinated and decaf coffee also stimulate the production of a hormone called gastrin, which promotes digestion and can increase our urge to go to the toilet. The acidic nature of coffee can also stimulate the bowels¹.

However, whether coffee is problematic can depend on the individual. “For some people with IBS and constipation a cup of coffee in the morning might help to get the bowel moving,” says Thompson.

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Irritable bowel syndrome

IBS stands for irritable bowel syndrome, and it is a long-term chronic condition of the gut (bowel) that causes episodes of tummy (abdominal) cramps, bloating and either constipation or diarrhoea. IBS is a problem with how the bowel works. There is otherwise nothing wrong with the bowel.

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Sweeteners

Many foods contain sugar-free artificial sweeteners, such as sorbitol and xylitol, but these can cause diarrhoea. According to some studies, sweeteners may affect the ‘good’ bacteria in the gut ². Also, chewing gum leads to more swallowed air, which can make gassiness and bloating worse.

Fruit juice

Drinking too much fruit juice can cause unpleasant symptoms for some people with IBS as it contains a sugarcalled fructose. In one study, around one third of patients with suspected IBS had fructose intolerance³. Fructose is found in higher quantities in juice, honey and sweets, as well as in fruits and some vegetables.

Some people, including those with IBS, are unable to fully absorb fructose in the small intestine, which can lead to bloating, stomach pain, and diarrhoea. As a result, the undigested fructose makes its way into the large intestine where it is fermented by bacteria, causing IBS symptoms.

It can help to limit the amount of juice you drink. However, Thompson adds that fruit is healthy and should not be completely cut out of a diet.

Fizzy drinks

Fizzy drinks can cause gas and bloating because of the carbonation. This can lead to excess gas that can irritate your digestive system. Additionally, regular fizzy drinks contain high levels of sugarand diet drinks contain artificial sweeteners, which can further aggravate the gut.

Fatty foods

Greasy or deep-fried foods that are high in fat, such as chips or pizza, can cause stomach cramps and diarrhoea in some people with IBS. It’s not known exactly why this is, but research has suggested that eating fatty foods can slow down the transport of gas in the gut⁴.

“High levels of dietary fat can also trigger a gut reflex called the gastrocolic reflex - this signals your colon to empty food once it gets to your stomach in order to make room for more food. For some people, this can cause diarrhoea immediately when fats enter the stomach.”

Milk

Lactose is a type of sugar found in cow’s milk and dairy products like cheese or ice cream. For some people with IBS, an inability to break down lactose - because of a lack of an enzyme called lactase - causes problems such as bloating, gas, stomach ache, and diarrhoea.

However, Thompson explains that lactase isn’t the cause of all cases of IBS. It’s important for people with IBS to identify their own triggers before changing their diet. If lactose does cause trigger IBS symptoms, you can swap cow's milk for alternatives such as oat or lactose-free milk.

Alcohol

Alcohol is believed to stimulate the digestive tract, which can lead to IBS symptoms. In the small intestine, alcohol can reduce the absorption of nutrients including carbohydrates. This can lead to gas and diarrhoea as these substances interact with bacteria in the large intestine. Like coffee, alcohol can speed up the movement of the muscles of the intestine, increasing the risk of diarrhoea in people with a sensitive gut⁵.

FODMAPS

FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) are sugars in certain foods that the small intestine absorbs poorly.

“These non-absorbable carbohydrates are found in many foods and are fermented by bacteria in the large bowel,” explains Thompson. “This can cause symptoms in people with IBS."

Foods which contain FODMAPs include - rye, milk, peaches, cherries, apples, pears, peas, beans, lentils, savoy cabbage and cauliflower.

How to manage the symptoms of IBS

Although there is no fix for IBS, it is possible to manage your symptoms. First, you should speak to your GP who will ask you about your symptoms, whether they come and go, how often you get them, and when you get them.

Before diagnosing IBS, your doctor may want to rule out other causes of digestive problems, such as coeliac disease - a condition caused by an allergy to gluten - mostly found in flour-based foods such as breads and pastas.

If you are diagnosed with IBS, it’s important to take note of foods which trigger symptoms before changing your diet. Keeping a food diary can help. Finding ways to relax, getting plenty of exercise, and trying probiotics may help ease your symptoms.

People who struggle with diarrhoea may benefit from cutting down on high-fibre foods, such as brown bread, as well as caffeine. It’s also important to drink plenty of water to avoid dehydration. However, if you are constipated, you should eat more fibre-rich foods, such as beans, carrots and linseeds. Your doctor may recommend medicines to control diarrhoea or relieve constipation.

Your GP or dietitian may recommend a diet which is low in FODMAP foods. “A dietitian is needed as the diet can be challenging to follow and nutritionally restrictive,” says Thompson.

Further reading

1. Acquaviva et al: Effect of regular and decaffeinated coffee on serum gastrin levels.

2. Spencer et al: Artificial sweeteners: A systematic review and primer for gastroenterologists.

3. Choi et al: Fructose intolerance in IBS and utility of fructose-restricted diet.

4. Serra et al: Lipid-induced intestinal gas retention in irritable bowel syndrome.