The FODMAP diet: Benefits, downsides and foods to avoid

IBS sufferers should avoid certain FODMAP foods such as garlic and artichokes - Getty

Irritable bowel syndrome (IBS) is no laughing matter. According to the medical research charity Guts UK, it is the most common digestive system disorder, with up to one third of the UK population experiencing symptoms. It causes stomach cramps and discomfort, diarrhoea, bloating and constipation, which come and go and can last for weeks – or months – at a time.

The exact cause of IBS is not yet known, although research suggests that it may be connected to the way that the brain and gut communicate. As a result, food moves too fast or too slowly through the digestive system. Experts believe that stress, bacterial infections and food intolerances can also cause IBS, and studies indicate that some people may have a genetic predisposition to the disorder. It’s also twice as likely to affect women as men.

There is no complete cure for IBS and it’s usually a lifelong problem, but all hope is not lost: with the right diet and lifestyle changes there is a way to control the symptoms.

Jump to:

• What is the FODMAP diet?
• Gut health, IBS and FODMAP sugars
• What are FODMAPS and where are they found?
• What are the benefits of following a FODMAP diet?
• Foods to avoid
• Complications with the FODMAP diet
• Foods to include
• How to start on the FODMAP diet
• What happens after the initial stage?
• A seven-day FODMAP meal plan 

What is the FODMAP diet?

The diet restricts the consumption of “FODMAPS” – four types of carbohydrates which are poorly absorbed in the small intestine and most likely to cause bloating, wind, constipation and diarrhoea in people with IBS.

FODMAP is an acronym standing for fermentable oligosaccharides, disaccharides, monosaccharides and polyols. These are all types of starches that can affect people with a sensitive digestion.

“The FODMAP diet removes these fermentable carbohydrates in order to reduce digestive symptoms. It should be seen as a timed intervention for IBS, rather than a diet to be followed longer-term,” says Anna Mapson, an IBS nutritionist and the owner of Goodness Me Nutrition.

“They are normal healthy foods, and if you don’t have IBS, you don’t need to be concerned about them.”

The FODMAP diet was first developed in 1999 by scientists at Monash University in Australia, with a view to improving the symptoms of IBS. It has since been adapted for the UK by researchers at King’s College London and implemented at Guy’s and St Thomas’ NHS Trust in London.

Gut health, IBS and FODMAP sugars

When high FODMAP foods – such as fruit, vegetables, grains, pulses and dairy – are eaten they move slowly through the digestive system, attracting water as they go. Once they reach the large intestine, our natural gut bacteria ferment these FODMAPS, producing gas in the process.

Most of us eat FODMAP foods every day without any issues, but the extra water and gas can cause issues for people with IBS, including constipation and/or diarrhoea, depending on how the bowel responds.

What are FODMAPS and where are they found?

FODMAPS are found naturally in many foods, as well as some food additives and artificial sweeteners. So while you may not be familiar with terms like “oligosaccharides” and “monosaccharides”, you’ve almost certainly eaten them on a regular basis.

What are the benefits of following a FODMAP diet?

“Many good quality trials have shown the diet to be effective in significantly reducing IBS symptoms,” says Laura Tilt, a FODMAP-trained registered dietitian. “Research shows that up to 75 per cent of people with IBS experience symptom relief with a low FODMAP diet.”

Mapson adds: “The diet tends to work more effectively on people who have diarrhoea-predominant symptoms, but some people with constipation can also get relief from bloating and gas.”

The main benefits of following the FODMAP diet are:

• Reduction in stomach cramps and discomfort
• Improved bowel function (less diarrhoea and constipation)
• Less bloating and gas
• Improved quality of life

According to the experts at Monash University, these symptoms should improve within two to six weeks of starting the FODMAP diet, but not everyone responds well. Most people find that their symptoms don’t disappear completely, and around one in four people don’t respond at all. This may be due to other lifestyle factors, such as stress, because they are not sensitive to FODMAPS, or due to an underlying condition that causes similar symptoms to IBS.

Foods to avoid

The FODMAP diet is challenging to follow, especially in the early stages when you eliminate all foods that are high in FODMAPS before gradually reintroducing them in order to establish which ones trigger symptoms.

Tilt explains: “The elimination part of the FODMAP diet lasts from two to six weeks. If symptoms improve within this time you’ll move to step two: reintroduction.”

So how do you know which foods to avoid?

Foods that cause an issue to those with IBS, according to the nutritionist Rhiannon Lambert, are:

• Beans
• Pulses
• Onion, garlic, leeks
• Wheat
• Cauliflower
• Apples
• Cow’s milk

“Additionally, foods which contain artificial sweeteners such as xylitol, sorbitol and erythritol are also known to cause symptoms,” says Lambert, the author of The Science of Plant-Based Nutrition. “If you check the ingredients of packaged foods you will spot this in everything from diet drinks and sugar-free confectionery to sauces and syrups.”

Complications with the FODMAP diet

Mapson recommends working with a FODMAP trained nutritionist as it can be difficult to work out what to avoid. She explains: “It’s quite hard for people to follow. You need to be aware of portions of foods, and there are strange contradictions. For example, green peppers are OK, but red peppers are limited to 50g. Broccoli heads are OK, but broccoli stalks should be limited.”

To complicate things further, you may need to follow this process more than once. Mapson says: “Food intolerances change over time, so it’s always good to revisit what you ruled out to see if things have changed. The reasons for the change are often down to gut bacteria changes in the small and large intestine.”

If you’re tempted to give a low-FODMAP diet a try so that you can identify your own personal sensitivities, intolerances and triggers, you will need to strictly avoid the following high-FODMAP foods for two to six weeks, and replace them with low-FODMAP alternatives.

This isn’t an exhaustive list, but should give you an idea of what to exclude:

• Vegetables: Artichokes, asparagus, cauliflower, garlic, peas, mushrooms and onion
• Fruit: Apples, cherries, mango, peaches, nectarines, pears, plums, watermelon, dried fruit, tinned fruit in apple or pear juice, juices from any of the fruits listed above
• Dairy products: Cow’s, goat’s and sheep’s milk, yogurt, fromage frais, processed cheese, ice cream
• Protein: Processed meats, marinated meats and poultry, most pulses and legumes including chickpeas, lentils, baked beans, kidney beans and butter beans
• Ready meals and snacks: Microwave meals, cakes, sauces, gravy, salad dressings, crisps and packaged snacks
• Grains: Breads made from wheat, rye and barley, breakfast cereals and biscuits
• Sugars and sweeteners: High fructose corn syrup, honey, agave nectar, snack bars, milk and white chocolate, sugar-free confectionery, including chewing gum and mints
• Nuts and seeds: Cashew and pistachio nuts

Foods to include

The initial stage of the FODMAP diet is very strict. Rather than trying to radically change the types of meals you prefer, the experts at Monash University recommend adapting your favourites with low-FODMAP alternatives. You might also find it useful to batch-cook some meals at the weekend, so that you have some packed lunches and frozen dinners ready to eat on days when you’re short of time.

Here are some low-FODMAP foods to include:

• Protein: Unprocessed meat, poultry or fish, eggs, walnuts, Brazil nuts
• Grains: Oats, rice, rice noodles, gluten-free pasta, spelt or gluten-free bread, quinoa
• Dairy alternatives: Lactose-free milk and yogurt, almond milk, firm cheeses, soy milk made from soy protein
• Vegetables: Green beans, broccoli, carrot, cucumber, lettuce, potato, tomato, aubergine
• Fruits: Firm bananas, cantaloupe melon, kiwi fruit, oranges and mandarins, blueberries, pineapple
• Oil: Olive oil, butter
• Condiments: Peanut butter, soy sauce, mustard, tahini, vinegars, Worcestershire sauce, miso paste

How to start on the FODMAP diet

Laura Tilt explains that there are three stages to the FODMAP diet, which are designed to help you work out if your symptoms are caused by sensitivity to FODMAPS.

Stage 1 – Elimination: “For two to six weeks you replace the high FODMAP foods in your diet with low-FODMAP alternatives to see if your symptoms improve.”

Stage 2 – Reintroduction: “If your symptoms improve, you move to the reintroduction stage, which lasts eight to 12 weeks. You reintroduce one type of FODMAP at a time back into your diet. You do this in increasing portion sizes for a set period (usually three days). This will help you learn which FODMAP foods trigger symptoms, and which you can eat comfortably and in what portion size.”

Stage 3 – Personalisation: “In this step you’ll return to a normal and varied diet, only avoiding the FODMAP foods that triggered symptoms during reintroduction.”

Laura adds: “With FODMAP intolerance, there’s usually no need to avoid foods entirely. Instead it’s about finding the amount you can tolerate without triggering symptoms. The aim is to include as many foods as possible whilst maintaining symptom control.”

What happens after the initial stage?

After the initial stage, you can carefully reintroduce some of your favourite foods, while monitoring your symptoms. You may find it useful to keep a food diary so it’s easier to keep track. Mapson says: “There is no specific order people should reintroduce foods. I advise clients to start with either whatever will make life easier with cooking (e.g. onions) or whatever they miss the most, or whatever they don’t think will cause a reaction.”

Catherine Rabess, registered dietitian specialising in gastroenterology and author of The 30 Plan, says: “Some people will find that they can manage small amounts of some foods occasionally without triggering symptoms, meaning they can include this food in their diet.

“Others have to be super-strict with the food group and avoid it completely as they can be more sensitive.” She adds: “It’s crucial to reintroduce the eliminated foods no later than eight weeks from starting the diet to pinpoint the foods that are triggering your symptoms.”

A seven-day FODMAP meal plan 

The following meal plan is designed to give you an idea of what the FODMAP diet looks like, but Tilt cautions about starting the plan without talking to a dietitian first.

“Check that you definitely have IBS, not other conditions which can present with similar symptoms, such as coeliac disease, IBD or diverticulitis,” says Mapson.

For more information on the FODMAP diet, talk to your GP, consult the FODMAP Dietitians Directory or the British Dietetic Association Directory.

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