By definition, only plant foods contain dietary fibre. Published values of fibre in foods vary greatly because of different analysis methods.
Wheat bran (commonly sold under the name of 'digestive bran') has the highest fibre content of all the items mentioned. Because of this, it should be regarded as a food supplement rather than as a food. (If you eat it as a food on its own - for example as a breakfast cereal - your fibre intake could in fact be too high!)
However, as shown above, an important result of the years of research into fibre is the realization that it can be used to lower the risk of some diseases and to treat them.
Can fibre help you lose weight?
Although there is as yet no firm evidence that fibre can be used to control weight problems, it can indirectly be of help if you're trying to cut down on kilojoule intake.
One of the effects of dietary fibre is that it 'dilutes' nutrients and therefore also the energy or kilojoule values of a food. In addition, foods which are rich in it need a good deal of chewing, which not only stimulates secretion of saliva but also means that it takes longer to eat them. In the stomach, insoluble fibre binds water and has a 'bulking' effect, while soluble fibre tends to form gels which slow down the emptying of the stomach contents into the small intestine. The result of these combined effects is that fibre-rich foods make you feel fuller for longer and less likely to head for the refrigerator half an hour after a meal! For this reason, and also to ensure that you get enough vitamins and minerals and won't suffer from constipation, any slimming diet should include ample fibre in the form of unrefined foods.
Effects of fibre in the small intestine
The small intestine is divided into the duodenum, jejenum and ileum and dietary fibre alters a number of functions throughout the area. Whereas refined foods are quickly digested and absorbed in the upper part or duodenum, fibre ensures that the food moves down into the jejenum and ileum, thus changing the site of digestion and absorption. The result is a slower and more prolonged or sustained absorption of several nutrients, which gives the body time to 'process' these nutrients.
In addition to water-binding and bulking effects, some fibre components have the ability to temporarily bind nutrients such as glucose and fats, as well as digestive enzymes, bile acids and possibly some toxic substances. This results in slower digestion of several nutrients and an increased excretion of bile acids - and perhaps also of poisonous substances.
