Dietary fibre is mainly needed to keep the digestive system healthy. Fibre comes from plant foods: cereal (bread, rice and pasta) vegetables, legumes, fruit, nuts and seeds. Eating at least 3 serves of vegetables, 2 serves of fruit and some cereal every day should provide adequate fibre in the diet.
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. 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 countries with low fibre diet.
A high fibre diet may not prevent or cure constipation unless you drink enough water every day. It is important to drink plenty of fluids each day to assist the action of fibre.
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.
Disorders connected with a lack of dietary fibre The most obvious effect of dietary fibre is on stool bulk.
Constipation is a significant problem in communities where fibre intake is low, but is virtually unknown when the diet is high in fibre.
Haemorrhoids are common and occur at any age in peoples of all races, both sexes and all occupations. There is also a direct association between haemorrhoids and a highly-refined low fibre diet. This causes constipation, that leads to straining at stool. Increasing the fibre content of the diet will prevent constipation and relieve the symptoms of haemorrhoids.
Increasing dietary fibre and using a bulking agent may be the only treatment needed for Irritable Bowel Syndrome.
Diverticular disease is unknown in rural Africans who eat a high-fibre diet, but is common in Western societies where many people have a low fibre intake. It is much less common in vegetarians.
The cause of bowel cancer is unknown but there is good evidence that dietary and other environmental factors promote it, at least in genetically-susceptible individuals.
People with type 2 diabetes benefit from an increase in dietary fibre and resistant starch. A high fibre diet is also likely to be low in fat and this is a further advantage.
Some soluble fibre found in oats, psyllium and barley, and also the pectin from certain fruits, can reduce blood cholesterol. Foods high in soluble fibre have benefits for those with high levels of cholesterol in blood, but a diet low in saturated fat is even more important.