Getting enough fibre on a low FODMAP diet

A drop in fibre intake is common when following a low FODMAP diet. In this lesson we look at why fibre is important, and how you can ensure you’re getting enough.

By Laura Tilt

What Is Fibre and What Does It Do?

Fibre is a type of carbohydrate that we don’t digest. It’s found in plant foods like wholemeal bread, fruits, vegetables, nuts, seeds and pulses (peas beans and lentils). 

Fibre is important for several reasons. Fibre sweeps waste through the gut, adding bulk to your poo, which helps prevent constipation.

Some types of fibre help normalise the consistency of poo, firming up loose stools, and making hard stools softer.

Fibre also feeds the beneficial bacteria that live in your gut. Once fibre lands in the large intestine, gut bacteria break down the fibre for energy - a process known as fermentation. The byproducts of fermentation are gases (released as wind!) and compounds known as short chain fatty acids, which help to keep the lining of the gut healthy.

Over the longer term, a high fibre diet can help to reduce the risk of bowel cancer, type 2 diabetes and heart disease.

Isn’t fibre a trigger for IBS symptoms?

Some types of fibre are more fermentable than others. This means they are rapidly broken down by gut bacteria and more likely to contribute to gas production. Eating lots of this type of fibre can increase IBS symptoms.

Highly fermentable fibres are found in a variety of foods like beans, lentils, onions and wheat and in cooked and cooled pasta and potato.  You’ll notice some of these foods are also high in FODMAPs.

There’s no need to avoid fibre if you have IBS, but changing the type of fibre you eat may be helpful if your symptoms don’t improve on a low FODMAP diet.

How Much Fibre Should We Be Eating? 

Current healthy eating guidelines for the general population (i.e. people without IBS) recommend that adults aim to eat 30 grams of fibre a day. This is regarded as a high fibre diet. On average, UK adults eat around 18 grams a day.

We don’t have enough good quality evidence to say what the optimal amount of fibre is for someone with IBS. But it makes sense to work towards the 30-gram target (or as much you can tolerate) because of all the health benefits.

Choosing less fermentable fibres will help you eat a higher fibre diet without increasing symptoms. If you are increasing your fibre intake, do so slowly over the space of a few weeks.

Going from a low to a high fibre diet can result in gas and bloating, so make one change at a time and drink plenty of fluid too.

Getting enough fibre on a low FODMAP diet  

It's common for fibre intakes to drop when following a low FODMAP diet, because many high fibre foods (like wholegrain bread and breakfast cereal, beans, peas and lentils and some fruits and vegetables) need to be avoided during elimination.

However with a bit of planning, you can still get enough fibre.

Here are my top tips to help keep your fibre intake up during elimination:

  • Choose rolled oats for breakfast. A serving is half a cup (about 40-50g)  
  • Snack on low FODMAP fruit or add a piece to your breakfast or lunch. Low FODMAP options include: firm bananas, blueberries, rhubarb, kiwifruit, pineapple, passion fruit and oranges.
  • Include two low FODMAP servings of vegetables with each of your meal. Examples include carrots, green beans, potato (skin on), spinach, spring greens, aubergine and green pepper.
  • Check the fibre content on food labels when buying low FODMAP bread and cereal products. Compare the ‘per 100g’ column to find higher fibre options. A high fibre option will contain 6 grams or more of fibre per 100 grams. Examples include quinoa, brown rice, gluten free multigrain bread, and rolled oats.
  • Add canned lentils/ canned chickpeas to a stew or salad. A ‘green’ or low FODMAP serve is 1/4 cup canned chickpeas or 30 grams of canned green lentils. Rinse the canned lentils/chickpeas well before use to help reduce the FODMAP content.
  • Snack on almonds. A ‘green’ or low FODMAP serve of almonds is 10 nuts
  • Add linseeds to your breakfast cereal or a low FODMAP yoghurt 
  • Snack on oatcakes with peanut butter