Soluble vs insoluble fibre

We’ve all heard that a diet high in fibre is essential. Here’s a little information to help you understand why.

Fibre (also known as roughage) is normally classified as either being insoluble fibre or soluble fibre, depending on if it dissolves in water or not. Both regardless of the type of fibre or its source will resist the assault of enzymes in the human digestive system. In other words, it will not be broken.

Dietary fibre is a group of complex carbohydrates that are not a source of energy to us humans because our digestive enzymes cannot break the bonds that hold fibre’s sugar units together, fibre adds no calories to our diet and is incapable of being converted into glucose.

So why is it important to eat fibre?

Soluble fibre forms gels when in the presence of water, which is what happens when apples and oat bran reach your digestive tract. Like insoluble fibre, soluble fibre can give you a sense of satiety without adding calories.

But just because you can’t digest dietary fibre it doesn’t mean it isn’t a valuable part of your diet. Au Contraire. Dietary fibre is valuable purely because you can’t digest it!

• Insoluble fibre: This type of fibre includes cellulose, some hemicelluloses, and lignin found in whole grains and other plants. This kind of dietary fibre acts as a natural laxative. It absorbs water, helps you feel full after eating, and stimulates the intestinal walls to contract and relax. These natural contractions, called peristalsis, move solid materials through the digestive tract and therefore play a major role in the elimination process.

By moving food quickly through the intestines, insoluble fibre may help relieve or prevent digestive disorders such as constipation or diverticulitis (infection that occurs when food gets stuck inside small pouches in the wall of the colon). Insoluble fibre also bulks up stool and softens it, reducing the risk of developing haemorrhoids and lessening the discomfort if you already unlucky to have them. Insoluble fibre is found in foods such as wheat bran, vegetables, and whole grains.

• Soluble fibre: This fibre, such as pectin in apples and beta-glucans in oats and barley, seems to lower cholesterol level. This tendency may be the reason behind why a diet rich in fibre appears to offer some protection against cardiovascular disease. Soluble fibre is found in oat bran, barley, nuts, seeds, beans, lentils, peas, and some fruits and vegetables. It is also found in psyllium, a common fibre supplement.

The following table shows you which foods are particularly good sources of specific kinds of fibre. A diet rich in plant foods (fruits, vegetables, grains) gives you adequate amounts of dietary fibre.

Fibre Where Found

Soluble fibre

Pectin Fruits (apples, strawberries, citrus fruits)

Beta-glucans Oats, barley

Gums Beans, cereals (oats, rice, barley), seeds, seaweed

Insoluble fibre

Cellulose Leaves (cabbage), roots (carrots, beets), bran, whole wheat, beans

Hemicellulose Seed coverings (bran, whole grains)

Lignin Plant stems, leaves, and skin