NHS Fodmap Diet: The Complete Guide

If you’ve been diagnosed with IBS, you’ve probably heard of the FODMAP diet. There’s a lot of evidence to show it works to reduce the symptoms of IBS, so many doctors and NHS dieticians now recommend it to their patients. If you’re wondering if it could help you, read on.
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What is the NHS FODMAP diet?
Does a Low-FODMAP diet help IBS?
What You Can Eat on a Low-FODMAP Diet
What You Can’t Eat on a Low-FODMAP Diet
How do I start a FODMAP diet?

What is the NHS FODMAP diet?

Scientists at Monash University in Australia developed the FODMAP diet in 2004 in a bid to help the growing number of people suffering from IBS symptoms.

So the NHS didn’t actually create the FODMAP diet. They just welcomed it as an effective way to help British people in the same way Australian doctors and dieticians had used it to help Australian people.

The diet works by restricting particular kinds of carbohydrates. ‘FODMAP’ is an acronym, with each letter representing one of those carbohydrates. So the official name is ‘low-FODMAP’, rather than simply ‘FODMAP’. FODMAPs are the things people on the diet should be trying to avoid.

NHS low fodmap diet infographic

FODMAP stands for:


The ‘fermentable’ part describes what happens in your large intestine when you eat FODMAP carbohydrates.

FODMAPs are types of carbohydrates that are not completely digested or absorbed in our intestines. When FODMAPs reach the small intestine, they move slowly, attracting water. When they pass into the large intestine, FODMAPs are fermented by gut bacteria, producing gas as a result (Source: NCBI).

The extra gas and water cause the intestinal wall to stretch and expand, causing pain and discomfort.


The name oligosaccharide comes from the Greek oligos (‘a few’) and sacchar (sugar). Saccharide is just the scientific name for sugar. Chemically, every type of sugar (carbohydrate) is made up of one or more units of molecules. Oligosaccharides are made up of ‘a few’ units.

Oligosaccharides are a part of the fibre found in the plants we eat. Two sub-types of oligosaccharides in particular —FOS and inulin—are present in a significant part of the daily diet of most of the world’s population.


Just as oligosaccharides are made up of ‘a few’ carbohydrate units, disaccharides are made up of two.

Also called a double sugar, a disaccharide is formed by two monosaccharide units, or simple sugars. The most common disaccharides are sucrose, maltose, and lactose.


Monosaccharides (from the Greek monos, meaning single) or simple sugars consist of one sugar unit that can’t be further broken down into simpler sugars. Examples of monosaccharides in foods are glucose, fructose and galactose.


Often called ‘sugar alcohols’, polyols are naturally occurring in certain fruits and vegetables and often added to foods as a reduced-calorie alternative to sugar.

Speak to a gut health expert.


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Does a low-FODMAP diet help IBS?

Low-FODMAP diets have helped a lot of people with IBS symptoms.

In fact, it seems to be the most effective dietary intervention to help reduce chronic IBS symptoms. (Source: JOURNALS SAGEPUB).

Many clinical trials have shown a high level of success from IBS patients who reduce or eliminate FODMAP containing foods from their diet. (Source: PUBMED NCBI), (Source: PUBMED NCBI), (Source: PUBMED NCBI).

Why Does a Low-FODMAP Diet Help IBS?

Many researchers have investigated how and why the low-FODMAP diet works.

The low-FODMAP diet changes your microbiome by restricting the carbohydrates in your diet that bacteria love to eat. As a result, they die off, or at least become less active (Source: NCBI).

The conditions below are all possible causes of IBS symptoms. There’s one thing they all have in common: dysbiosis (an imbalance of the microbes in your gut). While we don’t know exactly which microbes the low-FODMAP diet reduces, or whether they disappear temporarily or permanently, we do know that the low-FODMAP diet works through manipulating your gut bacteria (Source: NCBI).


In some cases, small intestinal bacterial overgrowth, also known as SIBO, contributes to FODMAP intolerance (Source: PUBMED NCBI).

Too many bacteria in the small intestine cause excessive fermentation of FODMAP carbohydrates, increasing gas levels and encouraging yet more gut bacteria to grow.

Lack of digestive enzymes

Some people—for a variety of reasons—don’t produce enough digestive enzymes in their guts to break down FODMAPs before they reach the colon (Source: NCBI). This can cause the bacteria there to have a party and multiply, giving off gases and prompting the colon to take in more water.


Emotional and physical stress contribute to the development of IBS symptoms, and could induce FODMAP intolerance for reasons we don’t understand yet (Source: PDFS), but an unbalanced microbiome is likely to blame. Stress changes the makeup of microbes in your gut (Source: PUBMED NCBI), which could be the reason why stress, FODMAP intolerance, and IBS are so closely linked.
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Find the root cause of your symptoms.

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What can you eat on a low-FODMAP diet?


  • Aubergine
  • Bamboo shoots
  • Bean sprouts
  • Broccoli
  • Cabbage (common and red)
  • Carrots
  • Celery (less than 5cm stalk)
  • Chickpeas
  • (1/4 cup max)
  • Corn (1/2 cob max)
  • Courgette
  • Cucumber
  • Green beans
  • Green pepper
  • Kale
  • Lettuce
  • Parsnip
  • Potato
  • Pumpkin
  • Red peppers
  • Scallions
  • Spring onions (green part)
  • Squash
  • Sweet potato
  • Tomatoes
  • Turnip


  • Bananas
  • Blueberries
  • Cantaloupe
  • Cranberry
  • Clementine
  • Grapes
  • Melons
  • Kiwifruit
  • Lemon
  • Orange
  • Pineapple
  • Raspberry
  • Rhubarb
  • Strawberry


All unprocessed meats and fish


  • Oats (1/2 a cup)
  • Quinoa
  • Gluten-free foods (breads, pasta, biscuits)
  • Buckwheat
  • Cornflour
  • Popcorn
  • Rice
  • Tortilla chips


  • Almonds (max of 15)
  • Chestnuts
  • Hazelnuts
  • Macadamia nuts
  • Peanuts
  • Pecans (max of 15)
  • Poppy seeds
  • Pumpkin seeds
  • Sesame seeds
  • Sunflower seeds
  • Walnuts

Milk alternatives

  • Almond milk
  • Coconut milk
  • Hemp milk
  • Lactose free milk
  • Oat milk (30ml max)
  • Rice milk (200ml max)


  • Butter
  • Dark chocolate
  • Eggs
  • Milk chocolate (3 squares max)
  • White chocolate (3 squares max)
  • Brie
  • Camembert
  • Cheddar
  • Cottage cheese
  • Feta
  • Mozzarella
  • Parmesan
  • Swiss

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What can’t you eat on a low-FODMAP diet?


  • Garlic
  • Onions
  • Asparagus
  • Beans (black, broad, kidney, lima, soya)
  • Cauliflower
  • Cabbage (Savoy)
  • Mange tout
  • Mushrooms
  • Peas
  • Spring onions (white part)


  • Apples
  • Apricot
  • Avocado
  • Bananas
  • Blackberries
  • Grapefruit
  • Mango
  • Peaches
  • Pears
  • Plums
  • Raisins
  • Sultanas
  • Watermelon


  • Chorizo
  • Sausages
  • Processed meat


  • Barley
  • Bran
  • Couscous
  • Gnocchi
  • Granola
  • Muesli
  • Muffins
  • Rye
  • Semolina
  • Spelt
  • Wheat (bread, cereal, pasta)


  • Cashews
  • Pistachios

Dairy products

  • Cow milk
  • Goat milk
  • Sheep milk
  • Buttermilk
  • Cream
  • Custard
  • Greek yoghurt
  • Ice cream
  • Sour cream
  • Yoghurt
  • Cream cheese
  • Ricotta cheese

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How do I start a FODMAP diet?

A low-FODMAP diet involves three phases:


In this phase, which can last from three to eight weeks depending on your response to the diet, you eliminate all high-FODMAP foods from your diet.


Once the elimination phase is over and your symptoms have gone (or are at least better), you can start reintroducing FODMAP foods into your diet one at a time, about every six days. This is so you can tell which foods trigger your symptoms.


This is where you return to a regular diet as much as possible, limiting only the FODMAP foods that cause IBS symptoms. Some people may be able to incorporate all or most FODMAPs back into their diet without symptoms, while others may struggle to reintroduce any at all.

Studies show (Source: PUBMED NCBI) that symptoms can continue to improve for a long time after reducing FODMAPs in your diet and even after reintroducing some of them. However, if all or many FODMAP foods continue to trigger your symptoms, you should seek the advice of a dietician, Functional Medicine Practitioner or Registered Nutritional Therapist.

Speak to a gut health expert.


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When is the diet appropriate?

A health professional may recommend a low-FODMAP diet if you are experiencing IBS symptoms.

In one 2014 study, a low-FODMAP diet improved the IBS symptoms of both constipation and diarrhoea. As FODMAPs are known to produce gas and draw water into the colon, it makes sense that people with abdominal pain and diarrhoea improve on the diet, but people with constipation can also improve. This might be because less gas and bloating could improve the muscular movements of the colon.

However many constipation sufferers report the opposite effect: their symptoms get worse on a low-FODMAP diet. This could be because FODMAPs have a natural laxative effect which speeds up their digestion. It could also be because if you don’t follow the low-FODMAP diet well, you could end up inadvertently reducing fibre, which can worsen constipation. A Functional Medicine Practitioner or Registered Nutritional Therapist can support you on your low-FODMAP journey and make sure you’re getting the right range and levels of nutrients.

Do I need to follow the FODMAP diet forever?

Both the NHS and Monash University say you should only follow the first phase of the low-FODMAP diet for three to eight weeks.

Fructans and galacto-oligosaccharides (the ‘F’ of FODMAPs) are prebiotics: that means they feed bacteria. So restricting them may starve beneficial bacteria (Source: NCBI). Studies have shown that a diet very low in FODMAPs reduces a type of bacteria called Bifidobacteria (Source: NCBI).

Studies have also demonstrated reduced Bifidobacteria in IBS patients compared with healthy controls (Source: NCBI), which suggests that the effect of a strict low-FODMAP diet might be counterproductive. Interestingly, the low-FODMAP diet has also been shown to reduce some butyrate-producing bacteria. As butyrate is a substance we can’t make ourselves (we rely on our bacteria to produce it) and is essential for the health of our colon (Source: NCBI), this proves that a low-FODMAP diet is not always a good idea for everyone.

However, there’s other evidence that some all-important mucus-degrading bacteria are actually increased with strict reduction of FODMAPs (Source: NCBI).

We clearly need more research on how FODMAPs affect the microbiome.

The bottom line? Opinions vary on whether you ‘have’ to start reintroducing FODMAPs after the initial exclusion phase. At Healthpath, we always try to balance managing your symptoms with tackling the root cause of them. So we suggest reintroducing FODMAPs systematically and carefully as soon as you’re ready.

Can I eat ‘this’ on the diet?

There are FODMAP diet lists all over the internet, and they’re all different. We recommend going straight to the source: the Monash University FODMAP web pages. You can also download a useful app for your phone for a small charge.

How does the Healthpath food plan differ from the low-FODMAP diet?

Our Functional Medicine Practitioners and Registered Nutritional Therapists create each person’s food plan based on the results of their tests and their individual symptoms. They use their own expertise and experience to decide what to recommend to each client. A low-FODMAP diet might be appropriate for one customer, but not for another.

How do you reintroduce food after the FODMAP diet?

The experts who created the low-FODMAP diet suggest an exclusion phase of all high-FODMAP foods for three to eight weeks. After that, they suggest that you reintroduce certain foods on a rolling six-day schedule: three days of consistently eating the food and three days of rest to watch your body’s reactions before you introduce the next food.

Except for the food you’re introducing, you should eat a low-FODMAP diet during the whole reintroduction period.

On the first days, eat one serving of a food from the FODMAP group you’ve chosen, increasing the serving size every day if your symptoms don’t come back. If they do, fast-forward to the three rest days. Then do the same for each FODMAP group.

The three rest days are for you to note down your symptoms and let your gut go back to ‘normal’ before you try again with the next challenge food.

Should I only follow FODMAP or can I also do another diet like paleo at the same time?

You could combine low-FODMAP with another diet but only for a short time, as long-term restrictive diets can lead to nutrient deficiencies. You should get professional advice—either from us, or from your GP, nutritionist or dietician—if you’d like to do this.

Can I do intermittent fasting whilst on the low-FODMAP diet?

Intermittent fasting has been shown to give many health benefits (Source: NCBI), but it isn’t for everyone. If you’re pregnant, have diabetes or have lived with an eating disorder, you shouldn’t try intermittent fasting. Talk to your GP if you’re unsure.

However if you’re healthy, fasting could do wonders for your gut health (Source: CAMBRIDGE), and there’s no reason not to combine it with the low-FODMAP diet.
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Key takeaways

  • The NHS often recommend the low-FODMAP diet for IBS because it’s had great results for a lot of people in reducing their IBS symptoms.
  • Our Registered Nutritional Therapists and Functional Medicine Practitioners at Healthpath use it for the same reason.
  • It’s important to remember that the low-FODMAP diet wasn’t invented as a long-term solution for IBS, and shouldn’t be used for longer than three to eight weeks.
  • The low-FODMAP diet starves gut bacteria. That’s how it works. So if it works for you, while it’s good news that your symptoms have improved, it’s also a sign that you need to pay your gut some attention.
  • The low-FODMAP diet addresses the symptoms of IBS, not the causes. At Healthpath, it’s our mission to dig deeper and tackle the reasons why FODMAPs became a problem for you in the first place.

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Alexandra Falconer MA (Dist) DipCNM mBANT is a Registered Nutritional Therapist specialising in IBS and related conditions. A graduate of Brighton’s College of Naturopathic Medicine, she is committed to fighting the root causes of chronic illness and bringing functional medicine to everyone who needs it.

Before her natural health career, Alex was a journalist and copywriter. She continues to write for magazines and media agencies, and now combines her two great passions—writing and health—by creating content that empowers people to claim their right to a healthy body and mind.
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