Fibre: What is it, what does it do and how do we meet out daily requirements
Updated: Mar 16
Fibre - hardly head grabbing news you would think but lately it’s been in the spotlight more than usual. All this media focused attention grabbing has been the result of the publication of a study commissioned by the World Health Organisation to collect and provide data for the release of new recommendations for optimal daily fibre intake and to determine which types of carbohydrate provide the best protection against non-communicable diseases (NCDs) and weight gain (1). The researchers included data from 185 observational studies which combined a total of 135 million human years and 58 clinical trials involving 4,635 adult participants conducted over a period of 40 years (pretty significant).
The comparison findings of the observational studies and the meta-analysis from the clinical trials indicate that there is 15-30% decrease in cardiovascular related and general mortality between those who eat the highest amount of fibre to those who eat the least. Consuming fibre-rich foods was found to reduce the incidence of coronary heart disease, stroke, type 2 diabetes and colorectal cancer by 16-24%. Higher daily intake was also associated with lower bodyweight and cholesterol. In terms of numbers, this amounts to about 13 fewer deaths and six fewer cases of heart disease for every 1000 participants. The greatest risk reduction was observed when daily intake of dietary fibre was between 25g and 29g (2), which is consistent with the recommendation of 30g per day in the UK. The challenge is that many people in the UK do not eat this amount on a daily basis. The major sources of fibre in the UK diet are cereals (bread, pasta, rice, breakfast cereal), vegetables and fruit (3).
Quality sources of fibrous foods include green vegetables, root vegetables, nuts, seeds, legumes, lentils and wholegrains.
The health benefits of consuming fibre are nothing new. Most of us are aware it offers us protection against bowel cancer, against the development of diverticula and haemorrhoids and supports cardiovascular health and improves bowel transit. But how many people knows it plays a vital role in the elimination of free hormones; the binding of fats and the release of sugar into the bloodstream; the regulation of inflammatory responses from the gastrointestinal flora and mucosal lining and the production of gastrointestinal immune defences (butyrate, short chain fatty acids). The connection between our gut and our immunity is strongly linked to what we eat and what we absorb and the diversity, location and numbers of our microbiome, of which fibrous foods provide food and fuel through the action of fermentation in the large bowel.
What is fibre?
Dietary fibre is a form of carbohydrate derived from plant based material (including nuts and seeds), that cannot be broken down and digested by our bodies’ enzymes in the small intestine. It passes through intact into the large bowel where it is fermented by bacteria or/and provides bulk to our stools. Both soluble and insoluble fibre remains undigested and so are not used for energy and are not absorbed into the blood stream (4).
There are two important types of fibre: water-soluble and water-insoluble. Soluble fibre contains compounds like pectins and beta glucans (found in oats and fruit like apples and berries) and insoluble fibre contains cellulose (a form of indigestible starch found in wholegrains and nuts). Fibre-rich foods typically contain both types (5).
What does it do?
Soluble fibre forms a gel in your gut when mixed with liquid which slows down the passage of food from the stomach to the small intestine. This helps to increase satiety (feeling fuller for longer which can be beneficial for maintaining a healthy weight) and prolongs the time sugar molecules are released and absorbed into the blood (helpful for diabetics and those with metabolic syndrome or PCOS) (5). Soluble fibre also binds to LDL cholesterol particles, so as it passes out of the body it takes some of these particles with it. Examples are oats, ground flaxseeds, psyllium husks, soft parts of apples and pears, nuts, seeds, beans, lentils, peas, barley, carrots, onions, bananas and strawberries. Soluble fibre supports the growth of beneficial bacteria in the bowel which helps to strengthen immunity and improve digestion.
Insoluble fibre or ‘roughage’ holds onto water and produces softer, bulkier stools, which helps to regulate bowel movement and increases transit time of food through the colon. It is good for constipation. Examples of dietary sources are bran, gluten free whole grains (brown rice, quinoa, buckwheat, millet, amaranth, sorghum), grape skins, berries, apple and pear skins, root vegetables (esp. skins), corn, whole wheat, rye, barley, green beans, green leafy vegetables, seeds and nuts. Insoluble fibre helps to regulate the correct pH in the intestines, encourages peristalsis and binds, transports and eliminates toxins and waste in the bowel over a faster time period (6). (6).
Recommended daily allowance
Age (years) UK recommended intake of fibre
2-5 15g per day
5-11 20g per day
11-16 25g per day
17 and over 30g per day
Food groups and fibre content
(1 cup is 100g)
1 medium pear, with skin – 5.5g
1 medium apple, with skin – 4.4g
1 medium banana – 1.5g
1 cup strawberries – 1.5g
½ cup blueberries – 4.2g
½ cup raspberries/blackberries – 4.0g
¼ cup prunes, dried or cooked – 3.6g
1 large kiwi – 2.7g
1 orange – 2.3 – 3.6g
1 medium peach – 2.9g
1 medium nectarine – 2.3g
2 plums – 2.2g
1 guava – 4.9g
5 kumquats – 6.2g
20 cherries – 3.4g
½ papaya – 2.6g
¼ cup dried figs – 3.7g
1 medium tomato, with skin – 1.3g
½ cup green beans, cooked – 8.8g
1 medium artichoke – 7g
½ cup artichoke hearts – 7g
1 medium sweet potato, cooked – 2.9 – 4.3g
½ cup green peas, cooked – 5.0g
½ cup squash – 5.0g
1 cup kale – 7.2g
½ cup courgette – 1g
½ cup Brussel sprouts – 3g
½ cup cooked parsnips – 2.7g
½ cup cooked cauliflower – 1.5 – 2.6g
1 medium potato with skin, cooked – 2.9 – 4.3g
½ cup spinach, raw and cooked – 2.3 – 3.7g
½ cup broccoli, raw and cooked – 2.5 – 3.0g
1 raw small carrot – 2.3g
½ cup cooked carrots – 2.2g
½ avocado – 6.7g
½ cup asparagus – 2.8g
½ cup corn, fresh or frozen, cooked – 1.7g
¾ cup oat bran – 5.0g
¾ bran flakes – 5.5g
1 slice rye bread – 1.4g
½ whole wheat pitta – 2.4g
1 slice whole wheat bread – 2.2g
1 tbsp. psyllium husks – 3.4g
¼ cup wheat germ – 3.5g
½ cup spinach or whole wheat pasta – 2.4g
2 cups of air popped popcorn – 2.4g
½ cup brown rice – 2.0g
¼ cup quinoa – 2.7g
½ cup lima beans, cooked – 4.8g
1 cup split peas, cooked – 16.3g
½ cup barley, cooked - 2.0g
½ cup lentils – 6.6g
¼ cup hummus – 3.7g
¾ cup beans (small white, yellow, cranberry, adzuki, black, pinto, kidney, navy, white), cooked - 8.6-13.8g
¾ cup of chickpeas – 5.5g
1 tbsp. ground or whole flaxseeds – 3g
½ tbsp. chia seeds – 3.7g
¼ cup coconut meat, dried or shredded - 7.8g
¼ cup sesame seeds – 3.4g
¼ cup almonds - 3.6-4.0g
¼ cup pumpkin or squash seeds - 3.7g
¼ cup sunflower seeds, without shell - 3.6g
¼ cup nuts (hazelnuts, macadamia, pine, pistachio), without shell - 3.1-3.3g
¼ cup walnuts (25g) – 2g
Examples of how we can meet the recommended amount
Oat porridge with nuts, seeds and ¼ cup blueberries – 9g
½ wholemeal pitta with lettuce, onion, tomatoes and cucumber with broccoli florets and hummus – 7g
Vegetable stir fry with kale, carrots, beansprouts, broccoli and brown rice – 14g
= 30g fibre
If we add a snack of berries or a banana and some nuts and seeds then we can further increase our intake.
Rye, barley and brown rice all contain high levels of insoluble fibre. Avoid rye and barley if you are removing gluten from your diet. Nutritious, high fibre gluten free alternatives are amaranth, millet, buckwheat and quinoa. Refined or processed grains like white rice, pasta and flour contain little fibre content because the bran has been stripped from the kernel.
Bowl of bio yoghurt with berries, tbsp. ground flaxseeds, pumpkin seeds and some almonds – 7g
Salad with seeds, spinach, tomato and cucumber, ½ organic apple with skin and ½ avocado - 15g
Bowl of blueberries and walnuts – 3.5g
Bowl of homemade squash and carrot soup – 5g
= 30.5g fibre
Tips to increase intake
Add ground flaxseeds to your morning oats. Sprinkle with seeds, nuts and fruit like sliced bananas or berries
Add beans or cooked lentils to salads
Sprinkle salads with pumpkin seeds and/or chopped walnuts
Make vegetable chilli with chopped celery, diced swede, tomatoes, chopped carrots, corn and kidney beans. Top off with fresh coriander and serve with brown rice
Buy your apples organic and eat the peel
Add seeds, nuts or dried fruit to your baking
Grate carrots or beets on salads
Sprinkle toasted pumpkin seeds onto soups
Add almonds, seeds and ground flax to bio yoghurt
Add sliced onions and small florets of broccoli, spinach or asparagus to scrambled eggs
Make a vegetable stir fry with carrots, broccoli, garlic, onions, asparagus, bean sprouts, sliced cabbage or kale
Make a lentil or chickpea curry with spinach and tomatoes and serve with brown rice
Snack on vegetables and hummus or nuts and seeds and berries
Prepare a mixed salad of brown rice or couscous and cold potatoes cooked in their skin
Replace mashed potato with a baked potato with skin left on or mash potatoes with their skins (always wash skins before cooking and try and buy organic)
Sprinkle sesame seeds onto stir fries, into soups and onto salads
Swap refined grains for wholemeal and bake with whole flour if the recipe permits
The act of fermentation can result in gastrointestinal symptoms like bloating. Building up fibre intake slowly will help to manage any discomfort and will give time for your digestive system to adapt. If you have been diagnosed with a condition like IBS you may struggle with high fibre intake. Please see a qualified nutritional practitioner or speak to your doctor for advice.
The Lancet. High intake of dietary fiber and whole grains associated with reduced risk of non-communicable diseases. ScienceDaily; Jan 2019.
Reynolds A, Mann J, Cummings J, et al. Carbohydrate quality and human health: a series of systemic reviews and meta-analyses. The Lancet. 2019; doi.org/10.1016/S0140-6736(18)31809-9.
Expert reaction to series of systematic reviews and meta-analyses about dietary fibre and the risk of non-communicable disease. Science Media Centre; Jan 2019
BNF. Dietary Fibre. British Nutrition Foundation; Jan 2017 (Reviewed Jan 2018).
University of California and San Francisco. Increasing Fibre Intake. UCSF Health. www.ucsfhealth.org/education/increasing_fiber_intake/
Dieticians of Canada. Food Sources of Fibre. Jun 2016. www.dietitians.ca/Downloads/Factsheets/Food-Sources-of-Soluble-Fibre.aspx
Colonandrectalsurgeon. Soluble Fiber and Insoluble Fiber Foods List with Fiber Grams. www.colonandrectalsurgeonskc.com/library/pdf/fiber-foods.pdf