Fibre in Foods
When advised about healthy eating or the dietary management of almost any disease condition, fibre and increasing one’s fibre intake is usually included as being important and offering many and significant health benefits. So although the message is simple – increase your fibre intake, as you will see when you read this brochure, the fibre story is actually not a simple one.
What Is Fibre?
Fibre traditionally forms part of the carbohydrate group of foods and is the name given to a group of materials found in the cell walls of plants, which give the plant its structure and form. Fibre is in fact a diverse group of compounds and as a result scientists have classified fibre in a number of ways including their chemical properties, their solubility and their physical properties. Recently nutrition scientists have divided fibre into two main groups:
Dietary Fibre – this is the non-digestible carbohydrate and lignin found in plants and includes what are known as plant non-starch polysaccharides (e.g. cellulose, pectin, gums, -glucans, hemicellulose and fibres contained in oat and wheat bran); plant polysaccharides (eg. inulin, oligosaccharides and fructans); lignins; and some resistant starch. It is this fibre that passes through your digestive tract largely intact and is thus also known as insoluble fibre.
Functional Fibre – this includes non-digestible carbohydrates that have been shown to have beneficial physiological effects in humans and includes non-digestible plant carbohydrates (e.g. resistant starch, pectins and gums); animal carbohydrates (e.g. chitin and chitosan) and commercially produced carbohydrates (e.g. resistant starch, polydextrose, polyols, inulin and indigestible dextrins). This fibre forms a gel when mixed with liquid and is also referred to as soluble fibre.
Total Fibre – is the sum of dietary and functional fibre.
Why Is Fibre Good For You?
Although not considered to be an essential nutrient, a lack of fibre in the diet will result in sub-optimal health. The research shows that there are many benefits provided by a regular intake of fibre in the diet.
Dietary fibre prevents constipation – High fibre foods together with a good fluid intake can help to make stools softer and easier to pass.
Total fibre may play a protective role in fighting colon cancer – The undigested fibre that passes into the large intestine is converted into short chain fatty acids by the bacteria that live in the colon. These short chain fatty acids seem to create an environment that is not conducive to the development of colon cancer. The most effective of the fibre foods seem to be the whole grains.
Dietary fibre helps with glycaemic control in diabetes – Fibre seems to lower the insulin response and slow glucose absorption which is beneficial especially to diabetics. Cracked grains (e.g. cracked wheat) and legume products are, it would seem, the most effective.
Functional fibre and a low fat diet can reduce the risk of heart disease – Soluble fibre found in oats, peas, beans, certain fruits and psyllium (found in cereal products) have been shown to have unique properties that lower total and LDL cholesterol. The amount of cholesterol reduction appears to be related to the amount of fibre consumed.
Dietary fibre may help with weight loss – This is thought to be due to fibre keeping you feeling fuller for longer, thus reducing the total food intake.
Fibre prevents dental decay – High fibre foods usually require more chewing which in turn causes an increased flow of saliva which helps keep the teeth clean.
The Department of Health has in its draft new regulations approved a number of claims linked to the fibre content of foods:
Foods that contain 2.5 g of total fibre per 100 g and 1.5 g of total fibre per 418 kJ will be allowed to claim ‘SOURCE of fibre’ on their packaging.
Foods that contain 5 g of total fibre per 100 g and 3 g per 418 kJ will be allowed to claim ‘HIGH fibre’ on their packaging.
Grain products, fruits or vegetables that are a source of fibre (without enrichment), trans fatty acid free and with a total fat profile in line with the South African prudent dietary goals will be able to make a health claim that reads: ‘Low fat diets, rich in fibre containing grain products, fruits and vegetables may reduce the risk of some types of cancer, a disease associated with many factors.’
Fruits, vegetables or grain products that are a source of soluble dietary fibre; low in saturated fat; low in cholesterol, trans fatty acid free and with a total fat profile in line with the South African prudent dietary goals will be able to make a health claim that reads: ‘Diets low in saturated fat and cholesterol and rich in fruits, vegetables and grain products that contain dietary fibre may reduce the risk of heart disease.
Foods containing at least 60 g whole oats (rolled oats, oatmeal) or 40 g oat bran, enrichment, that provides 3 g or more beta-glucan fibre per serving will be able to make a health claim that reads: ‘3 g beta-glucan fibre from 60 or 40 g whole oats daily or 40 g without oat fibre, as part of a diet low in saturated fat and cholesterol, may reduce the risk of coronary heart disease.
Foods containing 1.7 g of soluble fibre from the psyllium husk per suggested serving, low saturated fat, low cholesterol and low total fat will be able to make a health claim that reads: ‘Soluble fibre derived from foods such as psyllium as part of a diet low in saturated fat, cholesterol and total fat, may reduce the risk of heart disease.
How Much Should We Be Eating?
For Adults – most researchers agree that a daily intake of 20 to 35 g or 6 to 11 servings of grain products per day is sufficient. This should be provided from mixed sources, especially including the wholegrain cereals and vegetables. The ideal intake would be five portions of fruit and vegetables (with skins where possible) and at least two portions of high fibre cereal and grain products daily.
For Children – the recommendation for children older than 2 years is to increase fibre intake to an amount equal to or greater than their age plus 5 g per day, in order to achieve intakes of 25 to 35 g per day after the age of 20 years. For example, a child aged 5 years should be taking in at least 10g fibre per day (5 is equal to the age of the child + 5 g per day). Recommendations have also been made that children should increase their fruit and vegetable consumption to 5 or more servings daily.
What Common Foods Contain Fibre?
The following table shows the food sources and content (g/portion size) of dietary fibre
|Food source||Portion size||Total fibre (g)|
|Apple – with skin||1 medium||3.0|
|Bran flake cereal||188 ml||5.5|
|Butternut – cooked||125 ml||4.0|
|Corn flake cereal||250 ml||1.0|
|Fruitful Bran||188 ml||6.0|
|High Fibre Bran||125 ml||9.0|
|Honey Nut Crunch All Bran Flakes||125 ml||6.0|
|Kidney beans||125 ml||4.5|
|Oats Porridge||125 ml||2.0|
|Oatmeal – cooked||188 ml||3.0|
|Peanut butter – chunky||25 ml||1.5|
|Pear – with skin||1 medium||4.5|
|Potato – baked with skin||1 medium||4.0|
|Samp and beans||125 ml||4.0|
|Spaghetti – cooked||250 ml||2.0|
|White rice – cooked||125 ml||0.5|
|Whole-wheat bread||30 g||2.5|
Can Fibre Be Bad For You?
There are more benefits than disadvantages to following a high fibre diet, however, at very high intakes the following adverse effects may be noticed:
Cereal fibres can impair the absorption of some minerals, particularly iron and zinc, but this is due to their phytate content rather than their fibre content.
A higher fibre intake can result in flatulence, but this is usually dose related and your body does adjust to this over time. The trick is to start slowly and gradually increase the amount of fibre you eat, while simultaneously increasing fluid intake.
Dietary fibre can cause gas formation, resulting in gastro-intestinal distress for those suffering with Irritable Bowel Syndrome. Low dietary fibre diets are recommended for such individuals.
The FACS Message:
Fibre is important to our health and although the scientists may still be having a discussion on how to define and measure fibre, they all agree – everyone needs to ensure that they have a diet that is high in fibre. The best way to do this is to make a starchy food (preferably as unrefined as possible) the basis of most meals, include at least 5 servings a day of fruit and vegetables and take to reading the fibre levels declared on the foods that you buy.
For More Information:
- JOURNAL OF THE AMERICAN DIETETIC ASSOCIATION. 2002b. Position of the American Dietetic Association: Health implications of dietary fibre. Journal of the American Dietetic Association, 102(7): 993-1000.
- BLACKWOOD, A.D., SALTER, J., DETTMAR, P.W. & CHAPLIN, M.F. 2000. Dietary fibre, physicochemical properties and their relationship to health. The Journal of the Royal Society for the Promotion of Health, 120(4): 242-247.
- MAHAN, L.K. & ESCOTT – STUMP, S. 2000. Food, nutrition and diet therapy, 10th ed., W.B.Saunders Company
Reviewed for FACS by NEm (2016)