Dietary fibre

What is fibre? Fibre is made up of the indigestible parts or compounds of plants, which pass relatively unchanged through our stomach and intestines. 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.

In countries with traditionally high-fibre diets, diseases such as bowel cancer, diabetes and heart disease are much less common than in Western countries.

Research shows that many Americans are not getting enough dietary fibre. A diet low in fibre has been linked to: There are 2 categories of fibre – soluble and insoluble. Both are beneficial and we need to include them in our daily diets.

Most plant foods contain a mixture of both

What is soluble fibre? Soluble fibre soaks up water like a sponge and helps to bulk out our poo (faeces) so it can pass through the gut more easily. It acts to slow down the rate of digestion. Soluble fibre includes pectins, gums and mucilage, which are found mainly in plant cells.

One of its major roles is to lower LDL (bad) cholesterol levels.

It can also help with constipation

Good sources of soluble fibre include:

• soy milk
• speeds up the time that food passes through the gut

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 of insoluble fibre include: wholegrain foods.

Resistant starch, while not traditionally thought of as fibre, acts in a similar way. Resistant starch is the part of starchy food (approximately 10%) that resists normal digestion in the small intestine. Sources include:

• added to bread
• breakfast cereals

It can also be formed by cooking and manufacturing processes such as snap freezing.

Resistant starch is also important for gut 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. The digestive system is lined with muscles that massage food along the digestive tract – from the moment a mouthful is swallowed until the eventual waste is passed out of the bowel (a process called peristalsis).

It also important for other body functions, such as:

• reducing our risk of other conditions (such as heart disease
• some cancers). A high-fibre diet is protective against weight gain

High-fibre foods tend to have a lower energy density, which means they provide fewer kilojoules per gram of food.

As a result, a person on a high-fibre diet can consume the same amount of food, but with fewer Foods high in fibre are often bulky and, therefore, filling. 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 full

Fibre 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.

If you have diabetes, eating a diet high in fibre slows glucose absorption from the small intestine into your blood.

This reduces the possibility of a surge of insulin – the hormone produced by to stabilise blood glucose levels. Increasing dietary fibre and wholegrain intake is likely to reduce the risk of cardiovascular disease, It is also very likely that these observed health benefits occur indirectly, through the protective effects of ‘phytochemicals’ (such as ) that are closely associated with the fibre components of fruits, vegetables and cereal foods.

There is good evidence that soluble fibre reduces total blood cholesterol levels and LDL (bad) 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 (which includes 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.

Fibre is thought to decrease bowel cancer risk by increasing stool bulk, diluting possible carcinogens present in the diet and decreasing transit time through the colon.

Also, bacterial fermentation of fibre leads to the production of short-chain fatty acids, which are thought to have protective effects. Other research has found that a 10g per day intake of total dietary fibre equates to a 10% reduction in risk of bowel cancer. Research has shown that a high total fibre intake may reduce risk of breast cancer and a large-scale study also found that a higher fibre diet during adolescence and young adulthood may reduce women’s breast cancer risk.

Fibre is even more important for older people

The digestive system slows down with age, so a high-fibre diet becomes even more important. Some very high-fibre breakfast cereals may have around 10g of fibre per serve.

If this cereal is not accompanied by enough fluid, it may cause abdominal discomfort or constipation.

How much fibre do we need? Many adults do not consume enough fibre – on average, most Americans consume 20–25g of fibre daily.

The recommended daily fibre intake is: women = 25g of fibre each day

Boys (14 to 18 years) = 28g.

Most Americans do not eat enough fruit and vegetables, beans/legumes, or whole grain cereals - all of which are great sources of fibre. Simple suggestions for increasing your daily fibre intake include:

• Eat breakfast cereals that contain barley
• wheat or oats. Switch to wholemeal or multigrain breads
• 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: nuts or seeds instead of low-fibre cakes and biscuits. You do not need to eat many more kilojoules to increase your fibre intake.

Make sure you stick to the recommended intake and slowly introduce fibre into the diet to avoid any negative outcomes. A sudden switch from a low-fibre diet to a high-fibre diet may lead to some abdominal pain and increased ). This occurs when fibre binds these minerals and forms insoluble salts, which are then excreted.

This could result in an increased risk of developing deficiencies of these minerals in susceptible people. Also, it is better to get fibre from food sources rather than from fibre supplements, as these can aggravate constipation, especially if you do not increase the amount of water you drink daily. Dietary fibre is found in wholegrain cereals and fruit and vegetables Fibre is mainly a carbohydrate.

The main role of fibre is to keep the digestive system Conditions linked to low-fibre diets constipation haemorrhoids diverticulitis irritable bowel syndrome (IBS) overweight and obesity heart disease diabetes bowel cancer breast cancer Types of dietary fibre fruit and vegetables oat bran, barley, seed husks, flaxseed, psyllium legumes – dried beans, lentils, peas bran – wheat bran, corn bran, rice bran the skins of fruits and vegetables nuts and seeds dried beans Resistant starch acts like fibre many unprocessed cereals and grains unripe bananas potatoes lentils Health benefits of dietary fibre As dietary fibre is relatively indigestible, it adds bulk to our faeces (poo) and lowering blood cholesterol keeping our weight under control stabilising glucose – which is important if you have diabetes Dietary fibre and weight control kilojoules (calories) Dietary fibre and diabetes the pancreas Dietary fibre, cancer and heart disease type 2 diabetes , weight gain and obesity, and may lower blood

• pressure antioxidants Dietary fibre blood cholesterol angina heart attack Fibre
• bowel cancer risk Studies have shown that dietary fibre
• cereal fibre
• wholegrains are protective against some forms of cancer Fibre
• breast cancer risk Dietary fibre
• legumes Higher fibre food choices Fibre (g) (approx.) Lower fibre food choices Fibre (g) (approx.) 2 wholewheat cereal biscuits (e.g

Weetbix or Vita Brits) 2 1 cup puffed rice cereal 4 4 slices wholegrain bread 7 4 slices white bread 0 2 pieces of fruit (such as an apple and pear) 9 1 piece of fruit (apple) 1/2 cup canned fruit, undrained 7 4 1 cup frozen mixed vegetables 6 1/2 cup frozen mixed vegetables 3 1 small, boiled potato (with skin on) 8 1 cup of mashed potato 7 1 cup brown rice 7 1 cup white cooked rice 0 2 wholemeal dry biscuits 5 2 plain dry biscuits 4 25 almonds 0 1 slice plain cake 6 Total 4 5 A sudden increase in dietary fibre flatulence (wind) Also, very high-fibre diets (more than 40g daily) are linked with decreased absorption of some important minerals (such as iron , zinc and calcium Where to get help Your GP (doctor) Your maternal and child health nurse Dietitians United States 1800 812 942 Nutrition United States American guide to healthy eating .

Key Points

• Soluble fibre includes pectins, gums and mucilage, which are found mainly in plant cells
• Resistant starch is also important for gut health
• Fibre is even more important for older people
• digestive system slows down with age, so a high-fibre diet becomes even more important
• If this cereal is not accompanied by enough fluid, it may cause abdominal discomfort or constipation