Moreover about Dietary Fibre

Dietary fibre has been defined as the plant materials that are resistant to the human digestive enzymes. Dietary fibre includes non-starch polysaccharides, as described above, but the early methods for measuring the dietary fibre content of foods also resulted in the inclusion of non-car

bohydrate materials such as lignin (the woody part of plants), cutins, and waxes as well as some resistant starch Although the term dietary fibre is now well understood by the public, scientists investigating the potential beneficial effects of the complex prefer to be more precise and refer only to the specific non-starch poly saccharides, ignoring the resistant starch, lignins, and other materials....

This has resulted in some confusion over the dietary fibre content of food stuffs, as some countries (and even sometimes within countries) use total dietary fibre, and others non- starch polysaccharides, as the measurement on food labels and in food composition tables. The use of non-starch poly saccharides results in apparently lower levels of ‘unavailable’ material in the foods, as can be seen from the British food composition tables where both values are recorded.

Different foods contain different types of non-starch polysaccharides and this may have different effects on health. For example, cellulose and other non-starch poly-saccharides from cereals are less fermentable by gut bacteria than the so-called soluble non-starch polysaccharides found in foods such as oats and some fruits and vegetables. The former may be beneficial in terms of preventing constipation and some bowel diseases, whereas the latter, such as the beta-glucans in oats or guar gum from the cluster bean (Cyamopsis tetragonoloba), may help lower blood cholesterol levels and modulate blood glucose levels. Foods containing fibre supplements of various types are now being marketed as ‘health foods’ or ‘functional foods’.

Resistant starch

It used to be thought that all starch in foods was digested and absorbed, but it is now recognized that a certain proportion of the starch in foods is not digested in the small intestine and therefore enters the large intestine, alongwith the non-starch polysaccharides in the diet, where fermentation by gut bacteria breaks the materials down. Starch is resistant to digestion for various reasons. It may be enclosed within grains, which if not broken down by chewing survive the upper intestine intact the structure of the starch grains within the food may resist digestion reheating and subsequent cooling of the food may have resulted in the formation of retrograded starch whose structure again resists the action of amylase or the processing method itself may affect the structure of the starch. Whatever the reason, starch is probably the most

important substrate for fermentation, greater even than the non-starch polysaccharides simply because it is present in larger amounts.

Fermentation by bacteria results in the production of a variety of gaseous materials as well as water. Some of these materials are thought to help maintain the health of the large intestine (butyrate), others are absorbed and enter the energy systems of the body (acetate, propionate), while yet others are excreted as wind.