is largely a 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 carbohydrate. Simple
sugars consist of 1-2 sugar molecules such
as glucose, fructose, sucrose, maltose,
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 such as
xylose, arabinose, mannose. Dietary fibre
includes non-starch polysaccharides, oligosaccarides,
liginin (not a carbohydrate) and associated
1997 the World Health Organisation (WHO)
and Food Agriculture Organisation (FAO)
reviewed all the evidence regarding carbohydrates
and fibre and reported that:
is a nutritional concept, not an exact description
of a component of diet and that the use
of the term dietary fibre should always
be qualified by a statement itemizing those
carbohydrates and other substances intended
WHO/FAO recommended that carbohydrates be
defined in several ways:
1. Chain length:
this describes whether the carbohydrate
consists of one-two molecules (simple sugar),
a short chain (oligosaccharides) or a long
chain of sugar molecules (polysaccharides
or non-starch polysaccaride).
2. Glycaemic or
non-glycaemic: this describes
whether the carbohydrate can be digested
to provide glucose for absorption from the
small intestine; the corollary is, if it
is undigestible, it passes onto the large
intestine where it may be fermented by bacteria
or non-fermentable: this describes
whether the carbohydrate has survived digestion
in the small intestine, if it has survived
digestion, it is fermented (broken down)
by bacteria in the large gut (colon).
This is a new way of thinking and has not
yet been widely written about in text books
or in the lay literature. This article is
therefore based on the earlier definitions
is fibre found?
fibre is found in cereals, fruits and vegetables.
Fibre is made up of the indigestible parts
or compounds of the plant that pass relatively
unchanged through our stomach and intestines,
although bacteria in the large intestine
can partly digest fibre through fermentation.
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.
are broadly two categories of fibre and
we need to eat both in our daily diets:
- 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, oatbran, barley, seed
husks, flaxseed, psyllium, dried beans,
lentils, peas, soymilk and soy products.
It can also help with constipation.
- includes cellulose, hemicelluloses and
lignin, which make up the structural parts
of plant cell walls. One of its major roles
is to add bulk to faeces, and 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 - while not traditionally
thought of as fibre - acts in a similar
way. Resistant starch is a 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
large 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.
starch has some of the nutritional characteristics
of fibre but its effect on heart disease
risk factors are equivocal.
much fibre do we need?
Australians don't consume enough fibre.
On average, most Australians consume 18
to 25g of fibre daily. The Australian Heart
Foundation recommends that adults should
consume approximately 30g daily. Australian
and American experts have suggested that
a child should eat 10 or 5g of fibre, respectively,
plus an additional gram for every year of
age. For instance, a 10 year old child should
eat 15 to 20g of fibre per day.
which can arise from a low fibre diet include:
Constipation - small, hard and dry faecal
matter that is difficult to pass
· Haemorrhoids - varicose veins of
· Diverticulitis - small hernias
of the digestive tract caused by long term
· Irritable bowel syndrome - pain,
flatulence and bloating of the abdomen
· Being overweight and obesity -
carrying too much body fat
· Coronary heart disease - a narrowing
of the arteries due to fatty deposits
· Diabetes - a condition characterised
by too much glucose in the blood
· Colon cancer - cancer of the large
fibre is mainly 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.
health of the digestive tract
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 - from
the moment a mouthful is swallowed until
the eventual waste is passed out of the
bowel (a process called peristalsis). 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, but which speeds up the time that
food passes through the gut.
Fibre is even more important for older people.
The digestive system slows down with age,
so a high fibre diet becomes even more important.
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 which 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 and excessive
kilojoules (calories) are less likely to
for people with diabetes
Soluble fibre forms a gel when mixed with
liquid, which slows the stomach emptying
time and the absorption of carbohydrate
from the intestines. This helps to control
blood sugar levels. Glucose is a simple
sugar produced from the breakdown of carbohydrates.
In people who are sensitive to glucose,
such as those with diabetes, eating a diet
high in fibre slows the 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.
for the prevention of coronary heart disease
evidence that fibre protects you from heart
disease is strong. A study on
more than 43,000 US male health professionals
(Rimm et al. JAMA 1996; 275: 447-451) revealed
a strong link between consumption of fibre
and protection against CHD. Fibre in
vegetables, fruits and cereals was associated
with a 55% reduction in risk of fatal CHD,
but cereal fibre was most strongly protective.
There was a 29% lower risk of CHD for each
additional 10g cereal fibre eaten daily.
Recently, there has been a great deal of
interest in oatbran, since some studies
showed that regular intake of foods high
in soluble fibre - such as oat bran, baked
beans and soybeans - reduced blood cholesterol
only heart disease risk factor that has
been shown to be modifiable by dietary soluble
fibre is the level of plasma cholesterol.
A scientific review (Glore et al. J Am Diet
Assoc 1994; 94: 425-436) concluded that
comparable cholesterol lowering can be achieved
with daily consumption of 6-40g pectin,
8-36g gums (e.g. guar gum), 100-150g dried
beans/legumes, 25-100g oat bran and barley
bran (contain b-glucan) or 10-30g psyllium.
LDL cholesterol can be reduced by 5-10%.
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 (Zhang
AJCN 1992; 56: 99-105). A study from Finland
(Leinonen et al. J of Nutr 2000; 130: 164-70)
also demonstrated that 8 slices of whole
rye bread or whole rye crispbread daily
may help lower cholesterol in men with slightly
elevated blood cholesterol levels.
Not all of fibre’s protective powers come
from soluble fibre reducing plasma cholesterol
may also slow your rate of digestion, which
lowers insulin levels. Extra insulin can
raise your blood pressure, reduce HDL and
increase your risk of diabetes, all of which
can affect your heart. High fibre meals
are usually more filling, so you eat fewer
calories and this helps with weight loss.
Some chemicals formed by bacteria when they
break down soluble fibre may reduce blood
clots, which would lower the risk of heart
attacks and stroke.
recent study (Alberts et al. NEJM2000; 342
(15)) suggested that a high fibre diet may
not prevent colon cancer and the evidence
for fibre and prevention of breast cancer
is also inconclusive. Cereal
fibre has been shown by several studies
to protect against colon cancer. In the
Australian Polyp Prevention Project a combination
of low fat and wheat bran supplemented diets
(providing 11.5g fibre/day) was associated
with fewer new large adenomas over the 4
years of study (MacLennan et al. J Nat Cancer
Inst 1995; 87: 1760-6). A
study from the Arizona Cancer Centre involving
1429 men and women aged 40-80 who had recently
removed an adenoma from the bowel was
unable to show that taking a fibre supplement
(13.5g fibre/day) would prevent the recurrence
of an adenoma. In fact, multiple adenomas
were more common in the high fibre group
(Alberts et al. NEJM 2000; 342 (15)). The
different results obtained in these two
studies may be explained by the types of
used. In the Australian study an unrefined
wheat bran was used which was probably higher
in protective phytochemicals (phytoestrogens),
vitamin E, B6 and folate. The American study
used a more processed/refined fibre supplement.
by which fibre is protective?
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 very likely 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
to increase your fibre intake
Simple suggestions on how to increase 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
· Snack on fruit, dried fruit, nuts
or wholemeal crackers.
You don't need to
eat alot more calories to increase your
fibre intake; you can easily double your
fibre intake without increasing your calorie
intake by being more selective - see table
low fibre intake of less than 20g/day
cup rice bubbles
slices white bread
tablespoon peanut butter
cup canned fruit , undrained
fries large 110g
cup frozen mixed vegetables
cup white cooked rice
plain dry biscuit e.g SAO
slice plain cake 60g
cup commercial fruit juice
high fibre intake of more than 30g/day
can be easily achieved if you cosume wholegrain
cereal products and by eating more fruit,
vegetables and legumes and instead of low
fibre cakes and biscuits have nuts/seeds
as a snack or use in meals
slices wholemeal + wholegrain bread
e.g Taylors bread
tablespoon pure almond spread
cup frozen mixed vegetables
small boiled potato with skin100g
cup baked beans
cup white cooked spaghetti
whole grain dry biscuit e.g vitawheat
cup whole fruit juice e.g wild about
fruit hi-fibre apple juice
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, in fact, cause constipation.
sudden increase in fibre can have explosive
It should be noted that 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 to 35 g of fibre per day, and to gradually
introduce fibre into the diet to avoid any
negative outcomes. Adding
fibre to the diet from food sources is much
more preferable to adding fibre supplements.
Fibre supplements can aggravate constipation,
especially if daily water consumption is
not also increased.
of dietary fibre, especially cereal fibre
(both soluble and insoluble), is associated
with a lower risk of CHD
rich in soluble fibre reduce the level
of plasma cholesterol
a variety of whole grain cereals
to ensure an adequate intake of nutrients,
especially phytochemicals such as phytoestrogens
and phytic acid.
Carbohydrates in human nutrition. Report
of a joint FAO/WHO Expert Consultation,
Rome 14-18 April 1997, Rome: FAO, 1998
also HEC article "Grains
and cereals debate".
(Australian -Victorian Government website)
Updated: October 2002.