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what does fibre do for your body?

8th November 2017 by Jess

Our nutritionist Jess explains what fibre is and why it's such an important part of our diet.

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Did you know that the fibre in our diet has been decreasing ever since the Industrial Revolution?

This is bad news for our health, as low fibre means decreased microbial diversity in the gut. In fact, in 2015 the Dietary Guidelines Advisory Committee made fibre a "nutrient of concern".

Many people suffer with an array of gut-based illnesses or dysfunction, which can have broad-reaching impacts on many other areas of our health – here are some reasons why getting enough fibre is instrumental to keeping your body in great health.

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Many people suffer with an array of gut-based illnesses or dysfunction, which can have broad-reaching impacts on many other areas of our health. The impact of your food choices spreads beyond your microscopic friends.

Here are some reasons why getting enough fibre keeps your body in great health.

The process starts with dietary fibre feeding the growth of beneficial microbes, then the microbes contribute to:


Gut barrier function

Dietary fibre’s complex structures play a role in diversifying your gut’s microbes - that’s the collection of bacteria, fungi, yeast, and other microbes living in your digestive tract which is central to every aspect of health.

These bacteria, yeast, fungi, and more are pretty amazing. They increase your ability to metabolise a variety of substances you couldn’t produce without the enzymes they provide.

So basically, they work for you! Research has shown eating a variety of fibre-rich foods diversifies your microbiome, and people with a diverse array of gut microbes are better at responding to environmental challenges. Your gut also helps to facilitate the absorption of beneficial nutrients into the body, as well as helping to keep harmful substances from being absorbed.


Immune function in your digestive tract

Dietary fibre also impacts your gut’s immune function. That’s important.

The gut contains up to 80% of your body’s immune cells so it’s very key when it comes to keeping your body protected and fighting fit. A lack of fibre may negatively impact the natural intestinal barrier system, but increased protection can come when there are adequate amounts of fermentable dietary fibre.

This fermentation process has been shown to help maintain intestinal health in two ways: the first is increased cell proliferation (increase of the number of cells), and the second is increased cellular specialisation (when cells change to perform a specific job).


Endocrine (hormone) response

Feeding the growth of beneficial microbes with dietary fibre also supports healthy endocrine (hormone) response, nitrogen metabolism, and signalling between the gut, liver, and kidneys.


Liver health

Dietary fibre has been shown to increase the activity of antioxidant and detox enzymes in your liver - it can alter bile acid pools. These pools are involved in liver metabolism and the absorption of fats and fat-soluble vitamins. Dietary fibre also supports the microbiota that help generate secondary bile acids.



A surprising finding also links dietary fibre and the body’s fat-burning state (ketosis). This is accomplished by altering patterns of gene expression and the products of metabolism, the new patterns look like those found during the body’s fasting state (that’s when your body is burning energy from fat storage).


Nitrogen metabolism

Nitrogen is central to the findings about the kidneys and dietary fibre. When you feed your gut microbes dietary fibre, you increase your gut’s ability to contain more nitrogen.

In the gut, nitrogen acts as a fertiliser for the microbes, so the microbiome uses more of the nitrogen produced which keeps too much nitrogen gas from escaping through the portal vein to your detox organs. Reducing your kidneys’ nitrogen burden is important.

Dietary fibre also helps insulate your kidneys from other potential stresses. Not having enough fibre fermenting in your colon allows other substances to undergo fermentation. When things like amino acids ferment, they can produce harmful products that stress your kidneys, so keep your colon stocked with dietary fibre - for your kidneys’ sake.


Signalling between the gut, liver, and kidneys

The consequences in the gut are good for the liver and kidneys too, which makes total sense. Your gut supplies blood to these organs through the portal vein, so shifts in microbe activity and diet impact the liver and kidneys and support the important detox work these organs do.

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In summary, you can see that keeping your microbial buddies healthy and happy is important for maintaining good all round health. A great way to support a lush, diverse community of gut microbes is to eat a variety of fibre-rich foods.

Jess, graze nutritionist


The Scientific Advisory Committee on Nutrition (SACN), who looked at the role of fibre in maintaining good health, published these new recommendations in July 2015:

  • adults 16 years and over: 30g per day
  • 11-16 years: 25g per day
  • 5-11 years: 20g per day
  • 2-5 years: 15g per day
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Opting for more fibre rich foods is easier than you might think! Simply swapping plain flour for wholegrain goes a long way to increasing the fibre in your daily diet, like brown bread instead of white. Another good swap is choosing whole fresh fruit or fruit smoothies instead of fruit juices.

Breakfast: porridge oats with grated apple / pear
Mid-am snack: oatcake with nut butter
Lunch: sundried tomato and broccoli soup with rye bread and butter
Mid-pm snack: a handful of berries
Dinner: stir fry with wholegrain rice, broccoli, prawns, ginger and bean sprouts

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  5. Lembo AJ. Constipation. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 10th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 19.
  6. Threapleton DE, Greenwood DC, Evans CE, et al. Dietary fibre intake and risk of cardiovascular disease: systematic review and meta-analysis. BMJ. 2013;347:f6879. PMID: 24355537
  7. Kieffer DA, Martin RJ, Adams SH. Impact of Dietary Fibers on Nutrient Management and Detoxification Organs: Gut, Liver, and Kidneys. Adv Nutr. 2016;7(6):1111-1121.
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By Jess, graze nutritionist.

Our nutritionist extraordinaire, Jess trained at the Institute for Optimum Nutrition and is a registered practitioner with the British Association for Applied Nutrition & Nutritional Therapy. She's the creator of our health badges, to help you choose the snacks and boxes that are right for you. Check out everything from Jess on our blog, with recipes and tricks to help you keep making better choices, or go to her website at for even more.

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