Importance of Fibre in Diet
Dietary fibre is the part of foods which is NOT digested by normal processes before it reaches the large intestine. That is, while simple sugars, lipids and proteins are digested (broken down in to simpler molecules) in the stomach and first portion of the small intestine, fibre remains largely unchanged.
Fibre is a complex carbohydrate. The building blocks of all carbohydrates are different types of sugars and they can be classified according to how many sugar molecules are combined in the
• Simple sugars – consist of 1-2 sugar molecules; for example glucose, fructose, sucrose,
maltose and lactose.
• Oligosaccharides – consist of 3-10 glucose molecules joined together.
• Starch polysaccharides – have more than 10 glucose molecules joined together.
• Non-starch polysaccharides – have more than 10 sugar molecules; for example xylose,
arabinose and mannose.
How Does Fibre Work
Fibre works like a sponge in the body, it absorbs water and swells up so that your body can more
easily dispose of the waste contents of food. So it is very important to drink plenty of fluids for the fibre to work properly. Try to drink at least 8 cups of fluid a day. Because it is bulky and not rapidly broken down and converted into energy it will leave you feeling full and not feeling hungry soon after like sugary snacks do. This can help you manage your appetite and diet if you are trying to reduce your weight.
Fibre Rich Foods
You can find fibre in most breakfast cereals, particularly those that are unprocessed or have only light processing. Rice puffs have less fibre than Weetbix for example. Whole grains and wholegrain products such as breads and pastas are also high in fibre, as opposed to white bread and pasta/rice that are low in fibre and high in carbohydrates. Legumes are also high in fibre and the skins of fruits and vegetables contain most of the fibre of these foods.
Fibre in Food
Dietary fibre is found in cereals and grains, fruits and vegetables. Fibre is made up of the indigestible parts or compounds of plants, which pass relatively unchanged through our stomach and intestines. The main role of fibre is to keep the digestive system healthy. Other terms for dietary fibre include 'bulk' and 'roughage', which can be misleading since some forms of fibre are water soluble and aren't bulky or rough at all. It is believed that vegetarians have a lower risk of bowel cancer because they tend to eat more plant and grain products.
Fibre Keeps the Digestive System Healthy
Dietary fibre is needed to keep the digestive system healthy. It also contributes to other processes, such as stabilising glucose and cholesterol levels. In countries with traditionally high fibre diets, diseases such as bowel cancer, diabetes and coronary heart disease are much less common than in the West.
Most Australians don't consume enough fibre. On average, most Australians consume 18-25g of fibre daily. The Australian Heart Foundation recommends that adults should consume approximately 30g daily. Australian experts suggest that children should eat 10g of fibre a day plus an additional gram for every year of age. For instance, a 10 year old child should eat 15-20g of fibre per day.
Two Types of Fibre
There are broadly two categories of fibre and we need to eat both in our daily diets:
• Soluble Fibre – includes pectins, gums and mucilage, which are found mainly in plant cells.
One of its major roles is to lower blood cholesterol levels. Good sources of soluble fibre include
fruits, vegetables, oat bran, barley, seed husks, flaxseed, psyllium, dried beans, lentils, peas,
soymilk and soy products. Soluble fibre can also help with constipation.
• Insoluble Fibre – includes cellulose, hemicelluloses and lignin, which make up the structural
parts of plant cell walls. A major role of insoluble fibre is to add bulk to faeces and to prevent
constipation and associated problems such as haemorrhoids. Good sources include wheat
bran, corn bran, rice bran, the skins of fruits and vegetables, nuts, seeds, dried beans and
wholegrain foods. Both types of fibre are beneficial to the body and most plant foods contain a mixture of both types.
Resistant Starch
Resistant starch, while not traditionally thought of as fibre, acts in a similar way. Resistant starch is the part of starchy food (approximately 10 per cent) that resists normal digestion. It is found in many unprocessed cereals and grains, firm bananas, potatoes and lentils, and is added to bread and breakfast cereals as Hi-Maize. It can also be formed by cooking and manufacturing processes such as snap freezing.
Resistant starch is also important in bowel health. Bacteria in the bowel ferment and change the
resistant starch into short-chain fatty acids, which are important to bowel health and may protect
against cancer. These fatty acids are also absorbed into the bloodstream and may play a role in
lowering blood cholesterol levels.
Fibre Keeps the Digestive Tract Healthy
The principle advantage of a diet high in fibre is the health of the digestive system. The digestive
system is lined with muscles that massage food along the tract (a process called peristalsis) from the moment a mouthful is swallowed until the eventual waste is passed out of the bowel. Since fibre is relatively indigestible, it adds bulk to the faeces.
Soluble fibre soaks up water like a sponge, which helps to plump out the faeces and allows it to pass through the gut more easily. It acts to slow down the rate of digestion. This slowing down effect is usually overridden by insoluble fibre, which doesn't absorb water and speeds up the time that food passes through the gut. Very basically, fibre tends to ‘keep you regular’.
You Must Drink Lots of Fluid
A high fibre diet may not prevent or cure constipation unless you drink enough water every day. Some high fibre breakfast cereals may have around 10g of fibre per serve and if this cereal is not
accompanied by enough fluid it may cause constipation.
Fibre and Ageing
Fibre is even more important for older people. The digestive system slows down with age, so a high fibre diet becomes even more important.
Lowering Blood Cholesterol
Recently, there has been a great deal of interest in oat bran, since some studies showed that regular intake of foods high in soluble fibre – such as oat bran, baked beans and soybeans – reduced blood cholesterol levels. When blood cholesterol levels are high, fatty streaks and plaques are deposited along the walls of arteries. This can make them dangerously narrow and lead to an increased risk of coronary heart disease.
It is thought that soluble fibre lowers blood cholesterol by binding bile acids (which are made from cholesterol to digest dietary fats) and then excreting them. Cereal fibre seems to be more protective against coronary heart disease than the fibre from fruit and vegetables.
A Method of Weight Control
In many cases, people who are overweight or obese have been shown to lose significant amounts of excess body fat simply by increasing the amount of dietary fibre, especially soluble fibre, in their daily diet. Fibrous foods are often bulky and, therefore, filling. They also tend to be low in fat. Soluble fibre forms a gel that slows down the emptying of the stomach and the transit time of food through the digestive system. This extends the time a person feels satisfied or 'full'. It also delays the absorption of sugars from the intestines. This helps to maintain lower blood sugar levels and prevent a rapid rise in blood insulin levels, which has been linked with obesity and an increased risk of diabetes. The extra chewing time often required of high fibre foods also helps contribute to feeling satisfied. As a result, a person on a high fibre diet is likely to eat less food and so consume less kilojoules (calories).
Good for People with Diabetes
For people with diabetes, eating a diet high in fibre slows glucose absorption from the small intestine into the blood. This reduces the possibility of a surge of insulin, the hormone produced by the pancreas to stabilise blood glucose levels.
Conditions Linked to Low Fibre Diets
Eating a diet low in fibre can contribute to many disorders, including:
• Constipation
Hard and dry faecal matter that is difficult to pass. Can damage the intestinal lining and walls
and if it occurs chronically, can increase the risk of bowel cancer and haemorrhoids.
• Haemorrhoids
Varicose veins of the anus. Occurs when the veins of the rectum are put under chronic
pressure and strain, due to constipation and straining to pass faecal matter. Can be very
painful and if left untreated surgical intervention will be required.
• Diverticulitis
Small hernias of the digestive tract caused by long term constipation. Small abnormal sacs
(diverticulum) form within the intestine, trapping small particles of undigested food. This can
lead to inflammation and in sever cases ulceration.
• Irritable Bowel Syndrome
An illness of chronic, recurrent abdominal pain and cramping with associated flatulence and
bloating of the abdomen. It is difficult to diagnose with testing generally because it does not
appear to be due to an anatomical abnormality (you can see diverticulum or tumours). Often it
is diagnosed when a person complains of the symptoms above, along with bouts of constipation
and diarrhoea.
• Overweight and Obesity
Carrying too much body fat. Different types of fat storage have different health implications.
For example, carrying fat around the stomach is more dangerous than around the thighs. Low
fibre diets may contribute to obesity in a couple of ways. Firstly, fibre gives you a feeling of
being full and a high fibre diet is for this reason likely to be lower in calories than one comprised
of high fat, high GI (simple sugar foods that cause a sudden, dramatic increase in blood sugar
levels which results in the body over-reacting and sending levels plummeting. The low blood
sugar levels then stimulate appetite) foods. Also, high fibre intake appears to inhibit the
absorption of fat in the intestines.
• Coronary Heart Disease
A narrowing of the arteries due to fatty deposits. This process is hampered by high fibre diets
as fibre tends to lower blood cholesterol levels.
• Diabetes
A condition characterised by too much glucose in the blood. Regardless of the type of diabetes
glucose is not properly removed from the blood.
• Colon Cancer
Cancer of the large intestine.
The Debate About Diet, Cancer and Heart Disease
Studies that show a reduced risk of some cancers and coronary heart disease have received much attention. How these apparent health benefits arise is not fully understood. It is possible that these observed health benefits occur indirectly, through the protective effects of 'phytochemicals' (such as antioxidants) that are closely associated with the fibre components of fruits, vegetables and cereal foods. It has also been suggested that dietary fibre dilutes harmful substances and possible carcinogens present in the diet, thus reducing the gut's exposure to such compounds. In the case of bowel diseases, regular, healthy fibre intake will reduce the stress on the bowel as it wont be coping with bouts of constipation and irregular bowel motions etc.
Ways to Increase Your Fibre Intake
Simple suggestions for increasing your daily fibre intake include:
• Eat breakfast cereals that contain barley, wheat or oats.
• Switch to wholemeal or multigrain breads and brown rice.
• Add an extra vegetable to every evening meal.
• Snack on fruit, dried fruit, nuts or wholemeal crackers.
A daily intake of more than 30g can be easily achieved if you eat wholegrain cereal products, more fruit, vegetables and legumes and, instead of low fibre cakes and biscuits, have nuts or seeds as a snack or use in meals.
You don't need to eat a lot more kilojoules to increase your fibre intake; you can easily double your fibre intake without increasing your kilojoule intake by being more selective – compare the tables below.
Fibre Intake of Less Than 20g Per Day
Fibre (g) Kilojoules (kJ)
1 cup puffed rice cereal 0.4 444
4 slices white bread 3.0 1166
1 tablespoon peanut butter 2.7 610
1 piece of fruit (apple) 1.7 268
1/2 cup canned fruit, undrained 1.4 468
1/2 cup frozen mixed vegetables 4.3 102
Mashed potato 120g 1.7 336
1 cup white cooked rice 1.0 999
2 plain dry biscuit 0.4 150
1 slice plain cake 60g 0.6 643
1 cup commercial fruit juice 0.8 391
TOTAL 17.9g 5,557kJ
Fibre Intake of More Than 30g Per Day
Fibre (g) Kilojoules (kJ)
2 whole-wheat cereal biscuits (for example Weetbix or Vitabrits) 3.2 398
4 slices wholegrain bread 5.7 1085
1 tablespoon peanut butter 2.7 610
2 pieces of fruit (apple & pear) 4.9 515
1 cup frozen mixed vegetables 8.6 203
1 small boiled potato with skin, 100g 2.8 338
1 cup white cooked spaghetti 2.5 696
2 wholemeal dry biscuit 1.5 209
25 almonds 3.0 852
1 cup whole fruit juice 0.5 362
TOTAL 35.4g 5,118kJ
Increase your fibre intake gradually!
If you need to increase your fibre intake do so in increments. Suddenly and dramatically increasing your fibre intake can have explosive effects! A sudden switch from a low fibre diet to a high fibre diet can create some abdominal pain and increased flatulence. Also, very high fibre diets (more than 40g daily) are linked with decreased absorption of some important minerals, such as iron, zinc and calcium.
This occurs when fibre binds these minerals and forms insoluble salts, which are then excreted. This could increase the risk of developing deficiencies of these minerals in susceptible individuals.
Adults should aim for a diet that contains 30-35g of fibre per day and should introduce fibre into the diet gradually to avoid any negative outcomes. It is better to add fibre to the diet from food sources rather than from fibre supplements as these can aggravate constipation, especially if you don't increase the amount of water you drink daily. Also, by altering your dietary intake of fibre you should also be improving your vitamin and mineral intake as you eat more fruit and vegetables and whole grain foods rather than processed foods.
• Dietary fibre is found in the indigestible parts of cereals, fruits and vegetables.
• Animal products do not contain fibre.
• A diet high in fibre keeps the digestive system healthy.
• Most people in Western countries don't eat enough fibre.
• In western countries bowel cancer typically affects more people than any other cancer and it also results in more deaths per year than any other cancer.
To check your bowel health you can have a colonoscopy under anaesthetic (a lighted, flexible scope is inserted via the anus and extend through the bowel looking for polyps and early signs of tumours. In many cases small lesions can be removed during the colonoscopy). In some countries, including Australia people over 55 are mailed out faecal testing kits. A sample of faeces is sealed in a small container and returned by mail to a laboratory for testing. This sort of monitoring should be considered as important as a mammogram or prostate check!
Obviously these tests do not sound pleasant, however, they can, and for many people, have, saved lives. Bowel cancer detected early has a good prognosis, but if you leave it too late, the prognosis worsens dramatically. If a tumour grows large enough surgical removal may also result in such damage to the bowel that the region above the tumour will be redirected to a surgically created hole in the abdomen.
Patients then wear, for either a short time while the bowel heals, or for some, the rest of their lives, a colostomy bag to collect faeces. This is obviously a lot more unpleasant than a colonoscopy or the collection of a faecal sample.