Fibre: What is it and what does it do?

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 know it plays a vital role in all of the following:

• 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 bloodstream (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 whole grains and nuts).  Fibre-rich foods typically contain both types (5).

What does fibre do?

Soluble fibre forms a gel in your gut when mixed with a 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, whole grains (brown rice, quinoa, buckwheat), grape skins, berries, apple and pear skins, root vegetables (esp. skins), corn, whole wheat, 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).

Recommended daily allowance

The UK recommended intake of fibre for those aged:

• 2-5 years - 15g per day
• 5-11 years - 20g per day
• 11-16 years - 25g per day
• 17 and over - 30g per day

Examples of 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 courgette - 1g
• ½ cup Brussel sprouts - 3g
• ½ cup cooked parsnips - 2.7g
• 1 raw small carrot - 2.3g
• ½ avocado - 6.7g
• ½ cup asparagus - 2.8g
• ¾ bran flakes - 5.5g
• ½ whole wheat pitta - 2.4g
• 1 slice whole wheat bread - 2.2g
• ½ cup spinach or whole wheat pasta - 2.4g
• ½ cup brown rice - 2.0g
• ¼ cup quinoa - 2.7g
• ¼ cup hummus - 3.7g
• ¾ cup of chickpeas - 5.5g
• 1 tbsp. ground or whole flaxseeds - 3g
• ½ tbsp. chia seeds - 3.7g
• ¼ cup walnuts (25g) - 2g

Examples of how we can meet the recommended amount:
With grains (for 30g fibre)

• 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, bean sprouts, broccoli and brown rice – 14g

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. High fibrous, nutritious alternatives to wheat are amaranth, millet, buckwheat and quinoa. Refined grains like white rice, pasta and flour contain little fibre content because the bran has been removed.

Without grains (for 30.5g fibre)

• A bowl of yoghurt with berries, ground flaxseeds, pumpkin seeds and almonds - 7g
• Salad with seeds, spinach, tomato and cucumber, apple with skin and avocado - 15g
• Bowl of blueberries and walnuts - 3.5g
• Bowl of homemade squash and carrot soup - 5g

Tips to increase fibre 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 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/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 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-frys, into soups and onto salads.

References

1) The Lancet. High intake of dietary fibre and whole grains associated with reduced risk of non-communicable diseases. ScienceDaily. 10 January 2019. https://www.sciencedaily.com/releases/2019/01/190110184737.htm

2) Reynolds A, Mann J, Cummings J, et al. Carbohydrate quality and human health: a series of systemic reviews and meta-analyses. The Lancet, 2019 Jan. https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(18)31809-9/fulltext

3) Expert reaction to a series of systematic reviews and meta-analyses about dietary fibre and the risk of non-communicable disease.  Science Media Centre. 2019 Jan. http://www.sciencemediacentre.org/expert-reaction-to-series-of-systematic-reviews-and-meta-analyses-about-dietary-fibre-and-the-risk-of-non-communicable-disease/

4) https://www.nutrition.org.uk/healthyliving/basics/fibre.html

5) https://www.ucsfhealth.org/education/increasing_fiber_intake/

6) https://www.dietitians.ca/Downloads/Factsheets/Food-Sources-of-Soluble-Fibre.aspx

7) https://www.colonandrectalsurgeonskc.com/library/pdf/fiber-foods.pdf