Dietary fibre (also known as roughage) is derived from the plants including legumes, whole grains, Vegetables and fruits. It is not digestible in human body and is classified as soluble or insoluble fibre.

Soluble fibre with high viscosity and prebiotic properties is liable to fermentation process in the colon (large intestine) producing gases and some active substances. The insoluble fibre has inactive chemical characteristics while having the ability of water absorption during the digestion process and enabling easier elimination of fecal matters from the body.

The chemical structure of dietary fibre is made up of non-starch polysaccharide including cellulose, inulin, lignin, chitins, pectins and oligosaccharide, etc. Relatively all plants contain both soluble and insoluble fibres with different proportions. Plant sources provide noticeable percentage of insoluble fibre comprising seeds and nuts, flax seeds, skins of most fruits, whole grain food ranges and certain vegetables including celery, courgette, rhubarb, green beans, etc.

Soluble fibre is widely available in certain plant varieties, e.g. barely, oat, rye, legumes (beans and peas) and certain fruits (flesh rather than skins) comprising bananas, pears, berries and prunes. Some vegetables also provide high extent of soluble fibre such as carrots and artichokes. There is a concentration of soluble fibre in the inside of plants like onions and sweet potatoes (higher proportion of insoluble fibre is present in the skin of these plant types).

Fibres can provide substantial health benefits for maintaining adequate mechanism within the human body. Sufficient consumption of fibre-based food products can provide healthy gastrointestinal operation; suppressing inflammation of bowel or any major abdominal disorders (including diarrhea and constipation), inhibiting colorectal cancer (large bowel cancer), quick defecation (excreting harmful bacteria effectively), reducing the body weight as well as preventing obesity. Researchers have reported that fibre intake can considerably contribute to reducing cholesterol rate and therefore providing health condition on cardiovascular system.

The main function of dietary fibre is based on its modifying effects on the gastrointestinal tract; soluble fibre can be emulsified with the bile acids (in the small intestine)and therefore discouraging them from being introduced to the other parts of body. This subsequently affects on reducing the cholesterol in the blood and finally conserving the cardiac health. Soluble fibre is also able to inhibit the storage of sugar in blood.

As a result of fermentation of soluble fiber, short chain fatty acids are constructed which are believed to have numerous advantages. For instance they are able to regulate the rate of blood glucose and control the pH of colon; increase acidity and guard the lining of colon against the colorectal polyps development and facilitate absorbing minerals. Insoluble fibre is believed to be effective on lowering the risk of diabetic disease; however its main procedure for this protective function is still unclear.

There is a growing trend towards recommendation of more fibre consumption particularly in the US and Europe as it is nutritionally essential in order to maintaining a healthy system in the body. High extent of dietary fibre intake on a daily basis can have a remarkable effect on weight loss due to the fact that it can constitute some percentage of the whole daily intake and it is able to keep the dieter feel fuller quickly and the appetite for further eating is dramatically decreased. Insoluble fibre which is indigestible, does not contribute to any chemical changes of the food and is excreted from the body almost instantly.

However dieters should always consult with a qualified nutritionist when deciding to reduce weight in order to follow a healthy diet in an appropriate way. Officially more than 25 to 30 grams of fibre intake is recommended in the US by the American Dietetic Association (ADA) and above 18 grams per day is recommended in the UK by the British Nutrition Foundation.

The absorption of vitamins and minerals is not inhibited by the presence of ingested fibre in the body; no chemical bond is produced between fibre and vitamins/minerals. In fact, some studies have stated that soluble fibre is capable of developing most essential mineral absorption. When the absorption of vitamins and minerals (e.g. vitamin C, Ca, mg and zinc) is limited, it can be in association with some other plant compounds e.g. phytate and there is no relation between dietary fibre and restricting absorption of minerals.