Fibre in a healthy diet

What is fibre?

Dietary fibre is a term that is used for carbohydrates found naturally in plants that, unlike other carbohydrates (such as sugars and most starches), are not digested in the small intestine and so reach the large intestine (or colon) intact. There are many different types of fibre, found in a range of plant foods in the diet. Different fibre types can have different effects on our health.

You may have heard of ‘soluble fibre’ or ‘insoluble fibre’ – these are terms that are sometimes used to describe the types of fibre in our diet. Although scientific organisations do not use these terms anymore as they are not strictly accurate, you may see them being used. ‘Soluble fibre’ is usually used to refer to fibres such as pectins and beta glucans found in foods like fruit and oats, and ‘insoluble fibre’ to refer to fibres found in wholegrains, potatoes with skin and nuts.

Fibre can also be classified by its viscosity (viscous vs. non-viscous) and fermentability (fermentable vs. non-fermentable). Viscous fibres form a gel-like substance that “sits” in the gut. This can influence how quickly we absorb certain nutrients like sugar. Fermentable fibres can influence the number and type of bacteria in the gut.  Fibre-containing foods usually have a mix of different fibre types and so the key is to include a variety of plant foods to help us get all the benefits of fibre in the diet.

Why do we need fibre?

Fibre helps to keep our digestive system healthy and can help to prevent constipation. Including foods that have fibre in a healthy, balanced diet may help us keep a healthy bodyweight. Dietary fibre can also reduce risk of:

• Cardiovascular disease (heart disease and stroke) and type 2 diabetes - foods such as oats and barley have a type of fibre known as beta-glucan, which may help to reduce cholesterol levels if you consume 3g or more of it daily, as part of a healthy diet.  Beta-glucan may also help to control blood sugar levels as it can reduce the rise in glucose after a meal.  
• Bowel cancer - this may be because fibre helps food move more quickly through the gut. Obesity increases the risk of bowel and other cancers and so the fact that fibre-rich diets can protect against weight gain may also help to reduce bowel cancer risk.

Healthier diets are generally higher in fibre as they include plenty of fibre-containing plant foods such as fruit, vegetables, pulses, nuts, seeds and wholegrains. These foods also contain other important nutrients such as vitamins, minerals and bioactive plant compounds (like polyphenols), which may also play a role in the health benefits of fibre-rich foods.

Fibre and the gut 

We have probably all heard the phrase that fibre ‘keeps you regular’, but what does this mean? Fibre, especially cereal fibres such as those from wheat, barley and rye, can add bulk to stools by absorbing water, meaning that stools move more quickly through the gut and are softer and easier to pass. This means that having plenty of fibre, especially fibre from foods like wholegrain breakfast cereals, wholemeal bread or wholemeal pasta along with plenty of fluids and keeping active can help prevent constipation.

Fibre and ‘good’ bacteria

Research is increasingly showing how important the bacteria in our gut may be for our health, and that a fibre rich diet may help to increase the ‘good’ bacteria in the gut. 

It is estimated that we have around 100 trillion micro-organisms in our gut, sometimes called the gut microbiota – most of these are bacteria. There are many different species of gut bacteria, and these can be beneficial or harmful to health. The balance of the bacteria in our gut can be affected by several different factors, including our diet and lifestyle. Studies have investigated the effects of our gut bacteria on different aspects of our health including gut health (such as irritable bowel syndrome or constipation), obesity, immune function and brain function. The science in this area is still at an early stage and we do not know exactly what makes the gut microbiota ‘healthy’ or ‘unhealthy’. What does seem to be beneficial is having a variety of different types of bacteria in the gut, and particularly having more of the beneficial or ‘good’ bacterial.

Fermentable fibres such as such as inulins from onions, leeks, wheat and oats and galacto-oligosaccharides, found in pulses like beans, lentils and chickpeas provide a food source for ‘good’ gut bacteria. This can help to increase the numbers of bacterial species such as Bifidobacterium and Lactobacillus in the gut. When fibres are fermented by these bacteria, they produce gasses and compounds called short chain fatty acids, which can have beneficial effects. Short chain fatty acids provide a source of energy for the cells in the gut and may also stimulate hormones involved in appetite and glucose control.

We still need more research to understand how our diet may affect our gut bacteria but having a healthy diet with plenty of plant foods providing a variety of different types of fibre is likely to be beneficial for our gut microbiota.

How much fibre do we need?

Government guidance is that adults (those aged 17 years and over) should consume 30g a day. On average, we consume much less than this - about 20g per day. Children also need to increase their intake of fibre. Recommended intakes of fibre are shown below. 

How can we include more fibre in our diets?

Sources of fibre include:

• wholegrain breakfast cereals, wholewheat pasta, wholegrain bread and oats, barley and rye, brown rice
• peas, beans and pulses
• nuts and seeds
• potatoes with skin
• dried fruits

Getting at least five portions fruit and vegetables a day will also help us reach the recommended fibre intake.

As different types of fibre have different functions that are important for our health, eating a variety of fibre-providing foods is important.

To increase your fibre intake you could:

• Choose a high-fibre breakfast cereal, for example wholegrain cereals like wholewheat biscuit cereal, no added sugar muesli, bran flakes or porridge. Why not add some fresh fruit, dried fruit, seeds and/or nuts?
• Go for wholemeal or seeded wholegrain breads. If you or your family usually only like white bread, try the versions that combine white and wholemeal flours as a start.
• Cook with wholegrains like wholewheat pasta, bulgur wheat or brown rice.
• Go for potatoes with skins like baked potato, wedges or boiled new potatoes – you can eat these hot or use for a salad.
• For snacks try fruit (including dried fruits), vegetable sticks, rye crackers, oatcakes, houmous, unsalted nuts or seeds.
• Include plenty of vegetables with meals – either as a side dish/salad or added to sauces, stews or curries. This is a good way of getting children to eat more veg!
• Keep a supply of frozen vegetables so you are never without.
• Add pulses like beans, lentils or chickpeas to stews, curries and salads. Canned beans or chickpeas are a quick way to add fibre to a meal.
• Have some fruit, either fresh or canned in natural juice, for dessert or a snack.

If you need to increase your fibre intake, it is a good idea to so gradually to avoid gut issues like bloating and gas. It is also important to drink plenty of fluids (around 6-8 glasses per day for adults) and to try to be active for at least 150 minutes per week as these both contribute to keeping your gut healthy too. Find out more by reading our page on physical activity guidelines. 

Below is an example of foods that together provide more than the recommended amount of fibre over a day.

Our 7-day meal planner that meets fibre recommendations, as well as other recommendations for a healthy diet, can be found here.

How can we tell if a food is high in fibre?

Check the nutrition label to find out the fibre content per 100g of the food. A food is a ‘source of’ fibre if it has at least 3g fibre per 100g, and ‘high in’ fibre if it has more than 6g per 100g. You may also see ‘source of fibre’ or ‘high in fibre’ on the front of food packets.

How much fibre do children under 2 years need?

We do not have enough evidence to give a specific recommendation on fibre for children under 2 years but fibre should come from a varied diet once children start to receive solid foods, from the age of about 6 months. This can come from offering pulses, fruits and vegetables, as well as giving different kinds of starchy foods including wholegrains like wholemeal bread or pasta. However, under 5’s should not only be given wholegrain or high-fibre foods as they may fill a child up quickly so that they don’t get the energy and nutrients the need to grow and develop. Read more about this on our page on feeding your toddler.

Last reviewed June 2021. Next review due June 2024.