Dietary Fibre

Refined and processed foods have become a normal part of modern life, and it is now generally considered that we don’t eat enough dietary fibre. In ancient times, it has been estimated that we ate around 10 times more fibre in our daily diet than we do today, but our bodies have not adapted to this dramatic reduction.

So what is it?

Dietary fibre is provided solely by plant-based foods; also known as roughage, it comes in two forms: soluble and insoluble fibre. By soluble, we mean that it can dissolve in water, and is sometimes viscous and jelly-like in nature. An easy way to see soluble fibre is during the preparation of porridge: the gluey texture that appears after the oats have been soaked for a while is soluble fibre – they make the stools easier to pass. Insoluble fibre, on the other hand, passes through the digestive system in more-or-less the same state that it went in. Insoluble fibre absorbs water as it passes through the gut and is responsible for building up the stool (or faeces). So, fibre is essential for a good healthy gut. If you have constipation or diarrhoea, it’s possible that your fibre balance is wrong.

Fibre and health

It has been long understood that fibre is good for the heart. There have been a number of studies over the years that have shown that cholesterol levels (a well-documented risk factor for heart disease) are better in people who eat a diet higher in fibre than in those that do not. The precise mechanisms of this are still not fully understood, but it is believed that soluble fibre, particularly the viscous types, may block the uptake of cholesterol from the diet by holding onto it as it passes through the gut[1]. More recently, a prospective study showed that even if you have a heart attack, increasing fibre after the event lowers the risk of early death, which makes it potentially protective [2].

Some fibres ferment in the gut, and provide a great environment for the friendly bacteria. We will talk about bacteria and the gut in a future article, and how dietary fibre is important for their survival. This will be an important topic because fibre is preventative against bowel diseases including bowel cancer, not just because of its association with bowel flora, but also because it possibly “soaks up” carcinogens in the gut preventing them from contacting the gut wall, where they can damage the lining (called the epithelium) [3].

This fermentation process also releases a chemical called acetate, which recent (animal) studies have shown that it may instruct the brain to switch off appetite signals, suggesting that dietary fibre can make you feel full for longer [4]! So this great for people trying to lose weight, but not so great if you are a carb watcher!

The list goes on, there are studies showing fibre is protective against diabetes, high blood pressure, and obesity.

High fibre won’t be right for everyone.

Because fibres ferment in the gut, they can cause bloating and excess gas. If you have a diet low in fibre, introduce them slowly, a little more each day and slowing down if you notice symptoms. Fibre needs plenty of water to ensure a good stool bulk, so keep hydrated as you increase your consumption. Sufferers of irritable bowel syndrome, Crohn’s disease, ulcerative colitis or any bowel disorder should seek nutritional advice before increasing dietary fibre because your gut could be very sensitive to certain types of foods.

Sources of fibre

Typical sources in the Western diet include: wholegrain bread, brown pasta, brown rice, oatmeal, beans and pulses, sweet potatoes, nuts and seeds, fruits and vegetables.

Remember, fibre comes from plants, not animals. The higher the plant is processed (to make white flour for example), the lower the fibre content.

How much do I need?

We should aim to get about 18g of fibre every day. Currently, men average about 15g and women 13g.

If you switch to wholegrains rather than white foods (such as wholegrain pasta, bread and brown rice) and to sweet potato from white potato, you can get 18g of fibre in a day without too much effort. Here is an example of a day’s food plan:

1 medium bowl of porridge (low fat milk) + handful of blueberries = 2.2g fibre

1 medium banana = 3.1g fibre

220g portion of vegetable soup with one wholemeal roll = 6.2g fibre

Chicken curry (made with vegetables and chicken) with brown rice = 6g fibre
1 x 125g low fat fruit yoghurt = 0.5g fibre

Total fibre=18g
Other hints and tips to increase fibre:
– Add a tin of baked beans to stews or casseroles
– Add seeds to your morning breakfast cereal
– Choose bread that has seeds
– Try fish or chicken on a bed of puy lentils (you can cheat and buy Merchant Gourmet microwave packs) served with steamed vegetables or salad.
– Avoid foods that have been refined. White flour (in white bread and pasta) has had the fibre removed. Wholegrains retain it. We “refine” foods ourselves, without thinking, simply by peeling our fruit and vegetables. Skins are edible, just give it a good wash beforehand, and skins on potatoes really increase the fibre and are delicious roasted (in a small amount of olive oil of course!)

1. Vuksan et al. Viscosity rather than quantity of dietary fibre predicts cholesterol-lowering effect in healthy individuals. British Journal of Nutrition 2011; 106(9);1349-1352
2. Li et al. Dietary fiber intake and mortality among survivors of myocardial infarction: prospective cohort study. BMJ 2014; 348
3. Aune et al. Dietary fibre, whole grains, and risk of colorectal cancer: systematic review and dose-response meta-analysis of prospective studies. BMJ, 2011; 343
4. Frost et al. The short-chain fatty acid acetate reduces appetite via a central homeostatic mechanism. Nature 2014
Further reading:
British Nutrition Foundation: