Plants are made of carbohydrates, which are sugars synthesised into long chains to create both structural parts of the plant as well as food for seed growth. When we eat plants we eat both of these forms of carbohydrate in a ratio that is in balance without dietary needs. The carbohydrates used as structural components in plants are generally not digestible by humans. As a result we refer to this component as dietary fibre, and the edible component is termed starch.
What Is Dietary Fibre?
Dietary fibre is not a single compound but a group of indigestible carbohydrates. Sugars are bonded together in long chains, and the type of sugars and way they are bonded dictates the type of fibre. Fibres that are common in the human diet include cellulose, pectin, hemicellulose and gums. Humans do not possess the enzymes to break these down and so they are considered by many to not be absorbed, however, this is an erroneous belief in most cases.
Why Is Dietary Fibre Important?
Dietary fibre was once believed to be of relatively little important other than to add roughage to food to aid gastric transit. This viewpoint is still true, but more recently the role of fibre has expanded to other areas. Fibre is now known to provide energy to humans via its bacterial fermentation in the colon to short chain fatty acids. In addition, fibre is essential in delaying the absorption of glucose from many forms of carbohydrate and in this regard may prevent obesity.
Refined Carbohydrates And Obesity
Refined carbohydrates are the main form of carbohydrates in the Western diet. During the refining process, the bran and germ are removed from the grains and this leaves just the tasty starch endosperm. The difference between refined and whole grain cereals can be seen in comparison of whole grain and white bread. Removing the bran and germ also removes most of the fibre, and this is problematic because it causes a loss of control of blood sugar.
The Fibre Insulin Link
Fibre slows the absorption of glucose from carbohydrates and this allows a slow and gradual increase in blood sugar. This slow rise in blood sugar prevent the liver becoming overloaded with energy because it is more able to deal with the influx efficiently. Removing the fibre increases the speed of delivery and as a result the liver becomes overloaded with nutrients. This causes the liver to shift metabolism to the production of fats, especially if the meal contains the sugar fructose.
The insulin resistance caused by fructose and rapid influxes of glucose is a likely driver of obesity. This insulin resistance occurs because the fatty acids produced by liver overload are deposited in skeletal muscle and the liver where they interfere with the action of insulin. Fibre is known to prevent the risk of developing insulin resistance, in fact the simple act of eating tinned beans can significantly reduce this problem in diabetic subjects.