Dietary fibre is the indigestible portion of plant foods having two main components, soluble (prebiotic, viscous) fibre that is readily fermented in the colon into gases and physiologically active by products and insoluble fibre that is metabolically inert absorbing water throughout the digestive system and easing defecation. Chemically, dietary fibre consists of non-starch polysaccharides such as cellulose and many other plant components such as resistant dextrins, inulin, lignin, waxes, pectis, beta-glucans and oligosaccharides. Food sources of dietary fibre are often divided according to whether they provide (predominantly) soluble or insoluble fibre. Plant foods contain both types of fibre in varying degrees, according to the plants characteristics. The main action of dietary fibre is to change the nature of the contents of the gastrointestinal tract and to change how the other nutrients and chemicals are absorbed. Soluble fibre binds to bile acids in the small intestine, making them less likely to enter the body; this in turn lowers the blood glucose and cholesterol levels in the body.
The functions of dietary fibres are to add bulk to the diet, to attract water and turn it to gel during digestion trapping carbohydrates and slowing absorption of glucose, to lowers total and LDL cholesterol and to regulate blood sugar. The benefits are that they may reduce appetite and act as calorie free filler. They also lower variance in blood sugar levels, give sustained energy and reduce risks of heart attacks. The ADA recommends a minimum of 20-35gm fibre /day for a healthy adult, WHO recommends 30gm fibre; ICMR 2010 recommends the intake of 40 g/ 2000 kcal based on recommended energy intake.
Fibre plays a major role in conditions like Dyslipidaemia and Dysglycemia. Dyslipidaemia is an abnormal amount of lipids (e.g. cholesterol and/or fat) in the blood. Most dyslipidaemias are hyperlipidaemias, the prolonged elevation of insulin levels can also lead to dyslipidaemia. There are two major ways in which dyslipidaemias are classified which are the presentation in the body (including the specific type of lipid that is increased) and genetics or secondary to another condition. .
Low intake of fibre is related to risk factors of heart disease, obesity and diabetes. Soluble fibre like gums and pectic substances has hypo-cholesterolemic and hypo-triglyceridemic effects. It is important in atherosclerosis, coronary heart disease, hypercholesterolemia and hyperlipidaemia. Guar gum and oat bran alter post prandial lipid and lipoprotein composition when added to a meal fibre supplementation influence postprandial glycaemia, hyperlipidaemia. Examples of low Glycaemic Index(GI) 55 or less foods are most fruit and vegetables (except potatoes, watermelon and sweet corn), whole grains, pasta foods, beans, lentils while medium GI 56-69 are sucrose, basmati rice, brown rice and high GI 70 or more are Corn flakes, baked potato, some white rice varieties (e.g. jasmine), white bread, candy bar and syrupy foods.
Migration and transition in the dietary habits has resulted in the refined and high fat foods, which along with the sedentary life styles and lack of physical activity is leading to Dyslipidaemia and Disglycemia.