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Information on the low FODMAP diet


What is a low FODMAP diet?

Fermentable, Oligo-, Di-, Mono-saccharides and Polyols (FODMAPs) are short chain carbohydrates that are poorly absorbed in the small intestine. They can be found in a range of different foods:

  • Oligo-saccharides: e.g. fructans (found in wheat, rye and some vegetables) and galacto-oligosaccharides (found in pulses and legumes)
  • Di-saccharides: e.g. lactose (found in mammalian milk)
  • Mono-saccharides: e.g. free fructose (found in honey, some fruit and fruit juices)
  • Polyols: e.g. sorbitol and mannitol (found in some fruits and vegetables).

A diet low in FODMAPs is an effective treatment for gut symptoms such as bloating, wind, abdominal pain and an altered bowel habit. The low FODMAP diet was developed by a team at Monash University in Melbourne, Australia. It has been successfully adapted to the UK by researchers at King’s College London and implemented at Guy’s and St Thomas’ NHS Trust in London.

Why might FODMAPs affect my gut symptoms?

Once ingested, some FODMAPs do not get absorbed in the small intestine. They increase in the amount of water in the small intestine which may contribute to loose stools. They also pass along the gut to the large intestine where there are billions of bacteria which ferment them. This fermentation may result in gas production and symptoms such as wind and bloating. Reducing the intake of FODMAPs has been shown to improve gut symptoms in most people with functional bowel disorders like irritable bowel syndrome (IBS).

For more information on the low FODMAP diet, please watch the video below:

How can I follow the low FODMAP diet?

There are 3 stages to the low FODMAP diet:

  • Stage 1 Restriction: In this stage, you reduce your FODMAP intake by avoiding foods that are high in FODMAPs for 4 to 8 weeks as this period is considered long enough to identify if symptoms will respond to a low FODMAP diet.
  • Stage 2 Reintroduction: If your symptoms have improved following FODMAP restriction, it is important to reintroduce some high FODMAP foods. This will enable you to identify which FODMAPs you are most sensitive to, as well as how much of a high FODMAP food triggers your symptoms.
  • Stage 3 Personalisation : The long term aim of a low FODMAP diet  is to personalise your diet so you  only avoid foods that trigger your symptoms and you return to as normal a diet as possible. 
How successful is the low FODMAP diet?

The low FODMAP diet is effective for about 70% of people with IBS who try it. It works by improving the gut symptoms associated with IBS. There is no evidence that it works for non-gut symptoms that are sometimes associated with IBS, such as headaches and skin or joint problems.

I want to try the low FODMAP diet. What should I do?

The low FODMAP diet is quite a complex approach and so it is important that you receive good quality advice about how to follow the different stages. A registered dietitian, preferably one with experience of educating people on the low FODMAP diet, will help you to follow it carefully. He/she will ensure you follow a healthy balanced diet by providing you with ideas for suitable low FODMAP alternatives. Ask your GP or gastroenterologist (gut specialist) to refer you to a registered dietitian who is trained in the low FODMAP approach. A list of King's College London FODMAP-trained dietitians is available here.

Do I need to see a dietitian to follow the low FODMAP diet?

The diet is effective when FODMAP-trained dietitians provide the dietary advice. A recent evaluation has shown that 76% of patients that had seen a FODMAP-trained dietitian reported improvement in symptoms after being on the diet.

As this is a complex and restrictive diet, it is very important that you follow a well-balanced diet and meet your nutritional requirements. The diet should be individualised to each patient taking into consideration your usual dietary intake and symptom profile. Therefore, it is strongly recommended that you see a dietitian to follow the low FODMAP diet. A list of King's College London FODMAP-trained dietitians is available here.

Do I have to see an NHS dietitian?

There are FODMAP trained dietitians working in the NHS and privately. If you want to see an NHS dietitian ask your GP or consultant to refer you. Some private dietitians may also require a referral. Please note there are an increasing number of registered dietitians who are skilled in the delivery of the low FODMAP diet without having had formal training at KCL. A list of King's College London FODMAP-trained dietitians is available here. 

There is a lot of information on the internet about the low FODMAP diet. Can I try the diet myself?

The diet is not recommended to be used without specialist dietary advice from a registered dietitian. This is for a number of reasons:

Firstly, it is not as simple as following a list of ‘foods to eat’ and ‘foods not to eat’. High FODMAP ingredients are often hidden in packaged foods. You will need to learn about how to read food labels and how to make sensible decisions when eating out.

Secondly, as the low FODMAP diet is relatively new, much of the information available on the internet, and from other sources, may be out of date and create confusion regarding which foods to include and which foods not to include. This makes it difficult to work out how to follow the diet.

Thirdly, if you follow a low FODMAP diet without professional support from a registered dietitian, you may miss out certain foods from your diet that are essential to good health. 

Finally, if you do not follow the low FODMAP diet properly, it is unlikely to be effective. Therefore, it is best to get advice from a registered dietitian in the first instance.  

I have spoken to my GP or gastroenterologist and he/she has never heard of the low FODMAP diet

The low FODMAP diet is still a relatively new concept in the UK. It is recognised by national guidelines produced by NICE as an effective diet for managing IBS symptoms. Gradually more GPs and gastroenterologists in the UK are referring patients for advice from a registered dietitian who has experience in advising on a low FODMAP diet.





King's FODMAP-trained dietitians
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