The low-FODMAP diet for IBS

Niamh Hennessy
Lead Dietitian, Cromwell Hospital
03 November 2021
Next review due November 2024

The low-FODMAP diet involves limiting certain carbohydrates in your diet for a short amount of time. If you have irritable bowel syndrome (IBS), or another disorder affecting your gut, the low-FODMAP diet could help with your symptoms.

Here, I explain more about what it involves, and what you should do before considering it.

some garden vegetables on a bench

Living with IBS

IBS symptoms, such as tummy pain, bloating, constipation and diarrhoea, can make everyday life difficult. If you have IBS, you may notice that these symptoms are worse after eating. In fact, nine out of 10 people report that eating certain foods triggers their IBS symptoms.

The good news is that there’s a lot you can do to manage IBS. Reducing stress and staying physically active can be really helpful. Adjusting your diet can also make a big difference.

Before changing your diet, it’s important to get expert advice based on your diagnosis. Some of the symptoms of IBS can overlap with other gut problems such as coeliac disease or inflammatory bowel disease. It’s important to rule these out first. You really need to know your diagnosis and get expert advice before starting a special diet.

FODMAP diet: where to start

The low-FODMAP diet can help reduce IBS symptoms. But it’s not the place to start. Instead, make sure you have a healthy, balanced diet and eat three regular meals each day. This may help with your symptoms.

Next, work out what triggers your IBS symptoms. This could include alcohol, caffeinated or fizzy drinks, and spicy or fatty foods. Keep a food and symptom diary to help spot IBS trigger foods. This diary may also help a dietitian during any appointments.

It’s also important to stay hydrated. Drink at least eight cups of fluid per day, especially water or other non-caffeinated drinks, such as herbal teas.

Working with a dietitian

If you’re advised to follow a low-FODMAP diet, it’s important to work with a registered dietitian. Low-FODMAP diets are complex and should only be followed under the guidance of a qualified health professional.

Following a Low-FODMAP diet removes certain foods from your daily intake. If you don’t follow it correctly, there is a risk you’ll miss out on important nutrients.

The good news is, low-FODMAP is not a diet for life. You only follow it for six to eight weeks.

You will usually have an initial one-to-one education session to understand more about the diet and get tailored advice. Your dietitian will:

  • explain how FODMAPs can trigger symptoms
  • give you resources, such as a factsheet, booklets and recipes
  • tell you about alternative foods to FODMAPs

What does FODMAP stand for?

FODMAP stands for Fermentable, Oligo/Di/Mono-saccharides and Polyols. These are all types of carbohydrates that aren’t easily absorbed in the small intestine. They are found in many common foods. Here are some more details about what each of those words mean.

  • Fermentable – meaning that gut bacteria break down the nutrients, producing gas
  • Oligosaccharides – complex carbohydrates
  • Disaccharides – double-unit sugars
  • Monosaccharides – single-unit sugars
  • Polyols – sugars found in some fruits and vegetables, and in artificial sweeteners

All FODMAPs are potential triggers for IBS. But not all FODMAP foods cause the same symptoms. This can vary a lot from person to person.

How low-FODMAP diets work

The low-FODMAP diet is thought to work by reducing a process called fermentation in the gut. Fermentation happens when naturally occurring gut bacteria break down certain foods, and produce gases such as carbon dioxide, hydrogen and methane. In some people, this fermentation process can trigger troublesome gut symptoms.

The low-FODMAP diet is not a restricted or an ‘avoidance diet’. It’s a way to work out your tolerance to certain foods. This can help you make changes to your diet that will help with your IBS symptoms long-term.

The diet involves restricting all FODMAP intake for six to eight weeks. After this you’ll slowly reintroduce certain foods. This will help to identify which foods are causing your symptoms.

There’s still some debate about whether the low-FODMAP diet works. But evidence suggests that the low-FODMAP diet can help people with IBS.

High-FODMAP foods

Here are some of the foods that are avoided on a low-FODMAP diet. Please talk to your dietitian before taking these foods out of your diet.

  • Wheat
  • Rye
  • Onions
  • Garlic
  • Pulses (for example, beans and lentils)
  • Milk and dairy foods
  • Certain fruits, including apples and pears
  • Certain vegetables
  • Honey, plus some other natural and artificial sweeteners

Is a low-FODMAP diet for you?

If you’re struggling with IBS symptoms, talk to a registered dietitian with experience in this area. A low-FODMAP diet could make a real difference to how you feel.

But, the low-FODMAP diet is not for everyone. It’s just one of many choices that can help ease your IBS symptoms. Your initial education session with your dietitian is the most important part of making sure a low-FODMAP diet works.

From my personal experience as a dietitian, people with IBS who make small, sustained changes to their diet and lifestyle see benefits. It can improve your quality of life and help you to return to work and usual social activities.

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Niamh Hennessy
Niamh Hennessy
Lead Dietitian, Cromwell Hospital

    • Irritable bowel syndrome. NICE Clinical Knowledge Summaries., last revised June 2021
    • Irritable bowel syndrome (IBS) and diet: food fact sheet. British Dietetic Association., last reviewed January 2019
    • Irritable bowel syndrome (IBS). Medscape., last updated December 2019
    • Black CJ, Staudacher HM, Ford AC. Efficacy of a low FODMAP diet in irritable bowel syndrome: systematic review and network meta-analysis. Gut 2021. doi: 10.1136/gutjnl-2021-325214
    • Bellini M, Tonarelli S, Nagy AG, et al. Low FODMAP diet: evidence, doubts, and hopes. Nutrients 2020; 12(1):148. doi:10.3390/nu12010148
    • Varjú P, Farkas N, Hegyi P, et al. Low fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAP) diet improves symptoms in adults suffering from irritable bowel syndrome (IBS) compared to standard IBS diet: A meta-analysis of clinical studies. PLoS One 2017;12(8):e0182942

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