The main function of fibre is to keep the digestive system healthy and functioning properly. Fibre aids in speeding up the excretion of waste and toxins from the body, preventing them from sitting in the intestine or bowel for too long, which could cause a build up and lead to several diseases.
Fibre is only found in foods that come from plants. Foods such as meat, fish and dairy products don't contain any fibre. There are two different types of fibre soluble and insoluble, each helping your body in different ways, meaning a normal healthy diet should include both types.
Eating wholegrain cereals and plenty of fruit and vegetables helps to ensure that you are eating enough fibre.
Soluble fibre can be digested by your body. It may help to reduce the amount of cholesterol in your blood. If you have constipation, gradually increasing sources of soluble fibre like fruit, vegetables and oats can help soften your stools and make them easier to pass. Foods that contain soluble fibre include:
- Oats, barley and rye
- Fruit, such as bananas and apples
- Root vegetables, such as carrots and potatoes
- Golden linseeds
Insoluble fibre can't be digested. It passes through your gut without being broken down and helps other foods move through your digestive system more easily. Insoluble fibre keeps your bowels healthy and helps prevent digestive problems. If you have diarrhea, you should limit the amount of insoluble fibre in your diet. Good sources of insoluble fibre include:
- Wholemeal bread
- Nuts and seeds (except golden linseeds)
For people dieting or trying to lose weight, eating foods high in fibre will help you feel fuller for longer. If you do increase your fibre intake, it's important that you do so gradually. A sudden increase may leave you feeling bloated and cause stomach cramps.
It's also important to make sure you drink plenty of fluid. You should drink approximately 1.2 litres (six to eight glasses) of fluid a day and more while exercising. Fibre should be introduced gradually into the diet and can be done in a number of ways including:
- Start the day with porridge, high fibre cereals or wholemeal bread
- Eat more portions of fruit and dried fruit
- Eat potatoes with their skins intact
- Include chickpeas or lentils to salads, stews and curries
- Try to eat more raw fruit and vegetables
- Add seeds and nuts to salads or eat as a snack
- Switch to brown rice, brown bread and wholemeal pasta
- Buy foods containing whole grains
- Add barley to homemade soups
- Remember to also increase your water intake
Fibre and digestive health
Sources of less fermentable fibre can act as bulking (laxative) agents and help prevent constipation. For fibre to have the best effect on preventing constipation, an increase in fibre intake should be accompanied by an increase in fluid intake.
Some oligosaccharides (a type of fibre with a shorter carbon chain length) can be fermented by gut bacteria and may have a beneficial effect on gut flora. Eating a diet low in fibre is associated with diverticulitis (where the bowel wall becomes inflamed and ultimately damaged) and bowel (colo-rectal cancer) cancer. Evidence suggests that eating a diet rich in dietary fibre can help prevent diverticulitis and colo-rectal cancer.
Fibre and heart health
Some fermentable fibres eaten in large amounts can help reduce blood cholesterol levels. Diets rich in fermentable fibre, such as fruits and grains, and in particular oats, have been shown to reduce low density lipoprotein (LDL) cholesterol.
Fibre and type 2 diabetes
Dietary fibre has been shown to improve glycaemic control and has an important role in managing diabetes. Studies suggest that a high intake of dietary fibre reduces the risk of developing type 2 diabetes. There is also evidence specifically for higher intakes of cereal fibre and higher wholegrain consumption and lower incidence of type 2 diabetes.
Fibre and energy balance
Foods high in fibre tend to have a high volume and low energy density. These foods may help to reduce hunger and promote a sense of fullness and therefore play a role in the control of energy balance. Increased fibre intake can bring about a reduction in intake of other foods and a lower fat intake.