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NOTE: some high fibre foods, such as nuts, seeds, granola, are also high in fat, sugar and salt and should be eaten in moderation
What is fibre?
Fibre in food is the part you cannot digest. It will pass through; modified perhaps by the bacteria in your gut. Fibre comes exclusively from plants and is made up of a number of complex carbohydrates. There are broadly two types of fibre: soluble and insoluble; those that can dissolve in water and those that cannot. There are few calories, vitamins or minerals available
in the fibre fraction itself, but when fibre is obtained with the natural ‘whole food’, it will typically bring with it a lot of important vitamins, minerals or other protective ingredients. Green leaved vegetables for example, particularly kale, are high in Vitamin K that protects both our heart and bones.
Soluble fibre - includes for example fruit pectin, and gums and mucilages, such as those from linseed. Good sources of soluble fibre include generally all fruits, vegetables, seeds and grains (if they have not had the outer layers taken off), and especially the bran fraction of oats and barley. Linseed otherwise known as flaxseed, and all the ‘legumes’, such as beans, lentils, peas are good sources and there are several different kinds of chickpeas that are enjoyed by many when used in Indian and Greek cuisine as Dahl or Hummus. Similarly, ‘whole’ Soy products will have soluble fibre although the concentration in the ‘milks’ is quite low. Soluble fibre can help to lower blood cholesterol levels, and as a bonus helps with constipation.
Insoluble fibre – All the ‘whole food’ sources of soluble fibre also contain an additional insoluble fraction. This fraction includes the celluloses, hemicelluloses and lignin, which make up the structural parts of plant cell walls. Good sources are, for example all food grains if they come with their outer layers, especially the bran of wheat, sweet corn or rice, the skins of fruits vegetables, nuts, seeds, and of course, again, the legumes. Beans are a plentiful source. Insoluble fibre adds bulk to faeces and helps prevent constipation and associated problems such as haemorrhoids. It is worth noting that although rice bran, like oat and barley bran seems to bring extra useful properties, wheat bran on its own is mostly a ‘bulking factor’ and brings no special advantage for your heart, especially if it comes in a box with a large dose of salt and sugar.
What does fibre do?
Fibre is very useful for healthy bowel function and general health.
When fibre passes through the bowel it absorbs a lot of water, so it increases the bulk of the waste matter. This also makes the waste softer and increases the speed and ease with which it passes through the bowel. The digestive system is lined with muscles that massage food along the tract from the moment a mouthful is swallowed until the eventual waste is passed out of the bowel (a process called peristalsis). The two types of fibre both help to speed up the process. On the other hand, because sugar or easily digested starch is less concentrated in ‘high fibre’ foods then we are less likely get a ‘sugar rush’ after our meal. Compare for instance eating an apple and drinking apple juice.
Dietary fibre is needed to keep the digestive system healthy but it also contributes apparently in several ways to other processes, such as helping control blood glucose sugar levels. ‘High fibre’ ‘whole food’ diets are now standard recommendations for people suffering pre-diabetic conditions. This change in food seems to do more than control the sugar absorption, and can reduce for instance muscle ‘insulin resistance’ that leads to full diabetes. Similar food recommendations are made these days in order to encourage better control of cholesterol and blood fat levels. In countries with traditionally high fibre diets, who eat perhaps five times as much fruit and vegetables and use for instance ‘unpolished’ rice and ‘Dahl’ as mainstays for their food, diseases such as bowel cancer, prostate cancer, breast cancer, diabetes and coronary heart disease are very much less common than in “the West”.
Why is fibre important for weight loss?
A change to whole food’ is not the only way to lose weight, but the feeling of fullness which fibre produces can help people who are trying to lose weight to control their appetite. Many overweight people experience several months of relatively ‘effortless’ weight loss if they make a major change to a regime of ‘high fibre’ with lots of fruit and non-starchy vegetables. They are also recommended to take more exercise at the same time. Weight loss achieved in this way can lower blood pressure, lead to better sugar control, and reduce general levels of inflammation in arteries and joints.
Risk factors for development of heart disease include blood cholesterol, triglycerides and diabetes
Whole foods and also the bran fraction of oats and barley are helpful in lowering blood cholesterol. Higher blood cholesterol levels are associated with the build up over decades, sometimes from teenage years, of changes in the artery linings. These changes begin as “fatty streaks” and gradually go on to become inflamed and permanent plaques or ‘lesions’ in the walls of arteries. Any inflamed lesion can become very dangerous because if it leaks or discharges into the artery it is very likely to cause a clot. A sudden clot blockage is particularly dangerous (we know it as ‘heart attack’) but the gradual narrowing of the artery caused by the swelling, can itself lead to intermittent interruptions in blood flow and give rise to the disabling symptoms of ‘angina’.
It is thought that soluble fibre lowers blood cholesterol by helping us excrete it. (Bile acids are made from blood cholesterol and these acids help digest dietary fats). Bile will bind to soluble fibre and then be excreted with the fibre. It is not clear whether fibre fractions of cereals are more protective against coronary heart disease than the fibre from fruit and vegetables, so it is better to enjoy both, and the other protective ingredients that come with the natural ‘whole foods’.
How much fibre should we eat?
In the UK most people eat far too little fibre, on average about 12 grams a day or less. Ideally, adults should aim for an intake of more than 18 grams a day.. Eating a lot more fruit and bulky vegetables and grains etc. however, does have consequences. You not only will need to adapt your tastes and cooking, you will notice other effects!
A word of caution is relevant. If you would like to increase your fibre intake from a relatively low level, it is best to do it gradually. This is because a sudden increase may produce wind, bloating and stomach cramps - and changes in frequency of bowel movements. Learn to cook beans properly! A gradual increase will allow you to adapt to problems.
Post script: you should drink enough fluid
A high fibre diet may not prevent or cure constipation unless you drink enough water every day. A high fibre breakfast could contain around 10g of fibre per serving and if these cereals are not accompanied by enough fluid there is a possibility of constipation.
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