From what FODMAPs are to how the diet works & who it’s aimed at, a registered dietitian reveals the truth behind the buzzword 

Health-food fads come and go. But while topping your toast with avocado or adding chia seeds to your smoothie is definitely to be recommended taste-wise, when it comes to restricting food groups for health reasons, you should exercise caution. 

This is why we asked registered dietician, Dr Megan Rossi, aka The Gut Health Doctor and founder of The Gut Health Clinic, for the truth behind the low FODMAP diet trend, how the low FODMAP diet works, who it’s aimed at, and the potential benefits and side effects of the low FODMAP diet. 

What are FODMAPs?

‘It’s an acronym that stands for “fermentable oligosaccharides, disaccharides, monosaccharides and polyols”, which are essentially all scientific names for types of carbohydrates,’ says Dr Rossi.

These are: 

• Oligosaccharides, or fructans, are found in wheat, rye and some vegetables. 

• Disaccharides, or lactose, is found in mammalian milk.

• Monosaccharides, or free fructose, is found in honey, some fruit and fruit juices.

• Galacto-oligosaccharides are found in pulses and legumes.

• Polyols, such as sorbitol and mannitol, are found in some fruits and vegetables, as well as some sugar-free and low-calorie products.

‘These carbohydrates are found in a wide range of foods and can trigger digestive symptoms like bloating, gas and stomach pain in some people managing IBS,’ says Dr Rossi. 

How does the low FODMAP diet work & who is it aimed at?

The low FODMAP diet has been shown to be effective in the management of IBS-type symptoms in some people. 

‘We know the diet can be therapeutic for people who struggle with severe symptoms of IBS, a condition that affects around one in 10 people worldwide,’ Dr Rossi explains.

It may not be appropriate for everyone though and it’s recommended that it’s only followed once you’ve received an IBS diagnosis. ‘The low FODMAP diet is complex and you should only try it with the support of a FODMAP-trained dietitian or healthcare professional,’ advises Dr Rossi. 

It’s also worth noting that if you’ve been diagnosed with IBS, the low FODMAP diet isn’t advised as a first port of call. Initial recommendations to try include lifestyle changes, such as following a regular meal pattern, sitting down at a table to eat, making meals a digital-free zone and reducing intake of foods that are known to irritate the gut, such as spicy and high-fat foods, caffeine and alcohol. If these don’t work, other options include a two-week trial of a low-lactose or fructan-free diet. The NHS has created this handy webinar that provides further information.

If you’re still suffering with symptoms, it may be worth considering following a low FODMAP diet under the supervision of a FODMAP-trained dietitian. Ask your GP for a recommendation or referral if you’re not sure where to start. The diet involves swapping higher FODMAP foods with lower FODMAP alternatives for around four to eight weeks before reintroducing them and finding your own personal tolerance level.

According to Dr Rossi, the reintroduction and personalisation phases are key to finding your tolerance threshold, to support your gut bacteria and ensure you’re maintaining enough variety of fruits, vegetables and wholegrains in your diet. 

Be wary of where you get your intel from. ‘The information available on the internet is not overly accurate, as there are only a few places in the world that can measure FODMAPs,’ warns Dr Rossi. ‘That data has been protected by universities, mainly due to the fact that the diet risks becoming a ‘fad’ diet, and it’s not beneficial for the average person without IBS symptoms.

‘When we prescribe a low FODMAP diet, we provide clients with evidence-based resources developed by specialist clinics, such as King’s College London, which show what foods to restrict and alternatives to include.’

If you have been diagnosed with IBS and are looking for more details about the diet before seeking advice from a dietitian, you can gain access to some reliable information from the NHS’ low FODMAP webinar. 

What can’t I eat on the low FODMAP diet?

‘You might be surprised to know that a lot of the foods that are high in FODMAPs and are to be reduced are healthy,’ says Dr Rossi. 

Common FODMAPs that may be restricted or reduced during the four to eight weeks include:

• Fructose: a sugar found in honey, mango, sugar snap peas, jams and breakfast cereals. 

• Lactose: found in dairy products, such as mammalian milk and yoghurt and processed, reduced fat and cottage cheeses.

• Fructans: found in grains like wheat, rye and barley, onion, garlic and inulin.

• Galactans: found in beans and pulses.

• Polyols: artificial sweeteners like xylitol, sorbitol and mannitol, and stone fruit.

What can I eat on the low FODMAP diet?

Individual tolerance to FODMAPs varies. You may tolerate some foods on the list of foods to avoid while noticing digestive symptoms from foods low in FODMAPs. 

How much of a food you eat may also affect how likely you are to experience symptoms if you have IBS. 

There is a wide variety of food that you can eat on the low FODMAP diet. Here are some outlined by the NHS:

• Meat, fish and shellfish

• Eggs

• Oils

• Nuts (except pistachios and cashews) and seeds

• Herbs and spices

• Soya mince

• Quorn

• Tofu

• Table and caster sugars

• Artificial sweeteners other than xylitol, sorbitol and mannitol

• Maple syrup

• Golden syrup

• Fruits, including unripe bananas, blueberries, cantaloupe, grapes, kiwi, lemons, lime, honeydew and cantaloupe melons (except watermelon), all citrus (except a maximum of half a grapefruit), passionfruit, raspberries and strawberries

• Vegetables, such as alfalfa, pak choy, white and red cabbage, spring onions (just the green part), chives, spinach, kale, celeriac, courgettes, rocket, lettuce (iceberg, butter, radicchio, red coral), peppers, olives, cucumber, oyster mushrooms, aubergine, carrots, tomatoes, ginger and turnips.

• Garlic oil (instead of garlic)

• Gluten-free foods 

• All rice

• All white potatoes

• Oats and oat bran

• Buckwheat

• Polenta

• Quinoa

• Millet

• Non-wheat cereals

• Sourdough spelt bread made using 100% spelt flour and using the sourdough method

• Low lactose milk, yoghurt and ice cream

• Dark chocolate

• Full-fat cheeses, such as parmesan, brie, camembert and cheddar

• Butter

Is the low FODMAP diet good for you long term?

‘It isn’t recommended to follow the FODMAP diet long term,’ advises Dr Rossi. 

‘The diet involves three stages: the first being a four-to-eight week restriction phase, then a re-introduction phase and then the third personalisation stage, which contains many more FODMAPs than the restriction phase.’

In fact, being on the low FODMAP diet in the long term could kick things into reverse. ‘Research from the team at King’s College London has shown that going on a low FODMAP diet long term can actually reduce some of those beneficial good gut bacteria, so it’s certainly not recommended,’ adds Dr Rossi. 

Low FODMAP diet tips:

• Ensure you have access to credible FODMAP food lists. ‘Comprehensive FODMAP food lists are not readily available, which is why the evidence-based guidelines recommend you see a FODMAP-trained dietitian,’ says Dr Rossi.

• Create a low FODMAP shopping list before you head to the supermarket to remind you which foods to purchase or avoid.

• Read restaurant menus in advance, so you’re prepared when dining out. 

For further information on the low FODMAP approach and to read more of Dr Rossi’s guidance, check out her books Eat More, Live Well and Eat Yourself Healthy. Available to buy online.