What are Dietary Fibres?

To understand what dietary fibres are, we need to overview carbohydrates. Carbohydrates are important for body metabolism. They are high-energy molecules that our bodies use extensively to get energy. A Carbohydrate molecule can be of three types, based on its chemical structures:

• Monosaccharides: These are simple sugars with smaller molecules. The basic unit is one simple molecule, for example, glucose, fructose or lactose.
• Disaccharides: These carbohydrates are combinations of two simple sugars. Therefore, they are bigger than monosaccharides. For instance, lactose is the sugar found in milk. It is made up of glucose and galactose. Or, sucrose, which is the ordinary sugar present in sugarcane or sugarbeet or honey. One molecule of sucrose is the combination of one glucose and one fructose molecule.
• Polysaccharides: These are complex molecules made up of many simple sugar molecules bound together. So, you can imagine that polysaccharides are large molecules, sometimes composed of thousands of simple sugars.

Dietary fibres are forms of polysaccharides

In nature, polysaccharides come in different forms and have varied functions. For example, cellulose is a form of polysaccharide present in the cell wall of plant cells. Glycogen is another form of polysaccharide, in animal cells, like the liver and muscle, and its function is to store energy. Starch is another polysaccharide. It is the equivalent of glycogen in the plant world, with the same capacity of energy storage.

Now, what are fibres? Fibre is a general term for any plant-based, non-digestible and non-absorbable polysaccharide in our diet. Let me clarify it a little bit. From a dietary point of view, the polysaccharides that appear in our food are of two types. Some we are able to digest, like starch and some that our intestines can not digest. This latter group we call dietary fibres. So, fibres are not one type of molecule. They are a group of different molecules. Fibres come exclusively from plant foods.

Types of dietary fibre

Depending on their structures, dietary fibres are of two types:

Soluble fibres: These types of fibre molecules dissolve in water, or at least they may swell when put in water. Our intestinal bacteria can ferment these fibre molecules. Foods that contain these fibres are beans, lentils, oatmeal and fruits like blueberry.

Insoluble fibres: These fibres do not dissolve in water. Intestinal bacteria can not also metabolize them. These fibres are present in legumes and whole grains, like whole-wheat bread, brown or red rice. However, usually, fibre-containing foods have both types of fibre.

Dietary fibres and health

We need fibres because they have various health benefits. Here is a list of some of the positive impacts of fibres in lowering the risk of diseases:

• Lowering blood cholesterol level
• Help controlling blood sugar level
• Preventing colon disorders like hemorrhoids and diverticular disease
• Preventing and relieving constipation
• Lowering the risk of metabolic syndrome
• Lowering the risk of heart disease
• reducing the risk of breast cancer

How much fibre do we need?

The following table shows the amount of fibre adults may need each day.

Those interested in the more academic review of the role of dietary fibres can check this link. Also, I have already talked about intestinal bacteria. You can find some information here on fibres and our intestinal bacteria. We will also have engaging topics of foods that contain fibre, and the best ways to buy packaged foods that have fibre.