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IBS & the low FODMAP diet


The low FODMAP diet stands for ‘fermentable’ oligosaccharides, disaccharides, monosaccharides and polyols. This is a type of elimination diet used to control symptoms of Irritable Bowel Syndrome (IBS), but it can, with expertise, be used in a range of other gut conditions. The evidence-base for its efficacy is good and building steadily.


What are FODMAPs?

FODMAPs are short chains of carbohydrates found in a range of foods from milk through to fruit, vegetables, legumes (beans, peas and lentils) and sugar alcohols e.g. polyols. These foods don’t get absorbed in the small intestine properly and end up in the large intestine (colon) where they ‘ferment’. Think of FODMAPs as ‘prebiotics’ (non-digestible foods), because they build up, undigested in the colon, they feed our gut’s own bacteria and ‘ferment’, a bit like adding fertiliser to your garden. Probiotics on the other hand are the opposite – these a ‘friendly’ bacteria which boost bacteria numbers in our gut (a bit like compost?!).

How do FODMAPs cause IBS symptoms?


FODMAPs (prebiotics) once in the colon, draw in water, change gas levels and also cause bloating and distension, hallmarks of IBS. By changing the types of food you eat, that is to say eating foods that are better digested and absorbed i.e low in FODMAPs, there is less food left to feed bacteria and things are a lot calmer in the gut. Less bloating, flatulence, and a reduction in diarrhoea and even constipation. A word of caution though. Don’t embark on this diet before seeking medical advice. The diet involves a pretty aggressive restriction of a number of foods including gluten.


Why should I see a doctor before starting a low FODMAP diet?


It’s important if you think you might have IBS to see a doctor and get screened for coeliac disease. This is because if you start restricting gluten, and later respond to the diet, a blood test won’t show up for coeliac as you’ve got rid of the gluten in your diet! The low FODMAPs diet is a way of eating, you can’t just exclude a list of foods, it’s a complex process of screening food labels and making sensible swaps to help make the diet varied and balanced. It’s also only a temporary diet… reintroduction and re-challenge is crucial because there may be foods that can tolerate in your diet without issue. A broader diet means more flexibility and better bacteria levels in your gut. Remember you are the sum of the bacteria you feed!


Further reading: King's College London Information on the Low FODMAP diet

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