My mum used to call it roughage, and it is almost impossible to have missed the various health claims for what happens when you eat it.  Now we are even being told that certain bits of fibre are better than others; but what is it?


Fibre can be roughly defined as the indigestible part of plant based food. Measuring the amount of fibre in food has proved problematic, so as a result of these technical difficulties you will find reference to non starch polysaccharides (NSP) as well as dietary fibre in literature on the subject.  The differences is that dietary fibre includes NSP, but that NSP, as a defining category does not include all that is dietary fibre. Instead NSP is a method of measuring what in a food constitutes the indigestible portion.  The reason for referring to NSP is that NSP is the main component in plant cell walls, and therefore is the largest single contributor to the ‘fibre’ content of a food, and can be relatively easily measured to give food scientists a reasonably accurate and reliable measurement tool.


When you look closely at fibre it is best thought of as a family; its members are complex carbohydrates, and not all of them are fibrous in structure. There are two main classes of fibre, soluble and insoluble:


Soluble fibre

Soluble fibre dissolves in water forming a gel.  In the body this gel binds with other contents of the stomach. This means that digestion is slowed for whatever is bound in the gel. Soluble fibre does not pass through the intestines and out, once it reaches the colon it ferments.  This produces gas, but much more importantly fermentation results in additional nutrient absorption.  The fermentation action of healthy colon bacteria also releases short-chain fatty acids.  We are still discovering the health benefits of the colonic bacterial fermentation of soluble fibre, including the suppression of cholesterol production, stabilisation of blood glucose levels, as well as promoting a healthy immune system. Recently a number of soluble fibre products have been developed; they are coming to the market and being tested right now.


Insoluble Fibre

This type of fibre does not dissolve in water, and cannot be digested. Instead insoluble fibre passes through the body attracting water to it. Indigestibility and the fact that it draws water into the gastrointestinal tract make insoluble fibre a great way to prevent constipation. With a healthy insoluble fibre intake stools are soft and easy to pass – which is a great way to prevent diverticular disease – a condition that affects up to one in two people over 50, of those one in 20 with develop further complications.


Why Eat Fibre?

Fibre is essential to maintain a healthy gastrointestinal tract.  To maintain a healthy gut we need to eat a recommended 25-30g of fibre a day.  In surveys of the UK the average intake is between 12g and 15g, with similar results for the US.


The health benefits of fibre are still being investigated, but so far having a good fibrous diet has been linked to lower incidence of colon cancer and diverticular disease; as well as lowering cholesterol levels and the risk of heart disease, stroke and cardiovascular diseases.


For the athlete the health benefits long term are great, however, fibre has a more immediate benefit.  As mentioned before, fibre is essential for a healthy gastro-intestinal tract.  If the gut does not work right then all the healthy eating in the world amounts to very little.  A healthy gut maximises the absorption not only of proteins, fats, and carbohydrates, but also the micronutrients (i.e. vitamins and minerals) that are essential to health.  Fibre also promotes the action of healthy bacteria as well as proper function.  The benefit of this is that the body has a more active and effective immune system.  With the prevalence of upper respiratory tract infections in many a hard training athlete, this is a welcome boost.


Eating right for Fibre

Eating a healthy amount of fibre is not difficult, even if the average UK resident only eats half the recommended amount.  Eating five portions of fruit and vegetables a day should be enough to ensure a healthy fibre intake (interestingly the average UK resident averages around half the five a day).


Moving from an average intake to the recommended intake needs to be done carefully taking a week or more to build up.  If you don’t then you risk a dramatic decrease in transit time – otherwise known as diarrhoea.


Fibre and fluid

A healthy fluid intake, that is at least 1.5 litres a day, is always a good idea. When you eat a good fibre-full diet it is especially important. Dietary fibre acts much like a sponge, when you eat it the fibre tends to be dry, without fluid to lubricate it becomes a tough job to get it through to the other end. To illustrate this, get a sponge and try and push it through the cardboard tube in the middle of a toilet roll – dry this is not easy, wet the sponge and it slides through. The same is true for your body, if you do not supply the fluid you need to help the passage then some will be pulled from other parts of your body – but essentially the fibre is going through dry. Dry fibre passing through you is not healthy – it cannot perform its proper function without out adequate hydration. Like your brain, your gut performs best when well hydrated!


Good Fibre Foods

Broccoli is a powerhouse food packing a heavyweight nutrient punch in terms of vitamins and minerals with a healthy jab of fibre. Peas and beans have a healthy dose of fibre as do; sweetcorn, spinach, brussel sprouts, kale, turnip and greens all have fibre in abundance.  Potato skins are rich in fibre, and you don’t have to stick to just baked potatoes to eat the skin.  Instead of peeling, scrub with a vegetable knife and use as normal for extra fibre, vitamins and minerals.  Finally wholegrain and wholewheat food varieties are high in fibre and make a good contribution to a healthy daily intake.


As many may be aware, some forms of fibre are showing in studies to have health benefits when isolated. Beta-glucan isolated from oats is one such fibre fraction.  Outside the science lab there is no need to focus so precisely, science has not isolated the action of all the components of what we call fibre as of yet.  This being the case the best course of action is to eat a variety in a healthy diet to get all the possible benefits you can.


If it’s a fruit or vegetable and it is whole, it is going to have fibre. Even dried fruits, coconut and bananas make a healthy contribution.


Good Sources of  Insoluble Fibre




 brown rice


edible seeds










 wheat bran


 wholegrain breads


 wholegrain cereals


 wholemeal breads


 wholemeal cereals


 wholemeal pasta


 whole wheat flour

Good Sources of Soluble Fibre








 guar gum






















In the UK a food can be labelled ‘high fibre’ if it contains more than 6g of fibre per 100g of the product.


Bonus effects

If there were not already enough benefits to convince you that a health fibre intake is a dietary priority then it is worth remembering that foods which pack the fibre also pack vitamins and minerals.  By eating a variety of fibre rich foods you will also be getting a wide spectrum of vitamins, minerals, as well as phytonutrients each with their own unique health benefits; like the cancer preventative effect of the pigment lycopene found in tomatoes, or the anti-inflammatory action of lutein found in spinach. Don’t just think of eating fibre, but think of all that goes with it too.


A final note

Fibre can be broken down manually, cooking and chewing has some effect breaking fibre up a little. However the effect is not so much that it causes concern day to day.  Blending, juicing and smoothie making do substantially alter the structure of the fibre component of fruits and vegetables. Mechanically breaking the structure to make a liquid out of fruit and vegetables effectively destroys a substantial part of the fibre content and this is why to date a juice or smoothie still only counts as one of your five a day. Depending on what is removed when the drink is made you may find that the vitamin and mineral count has suffered along with the fibre content.



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