Introduction

Today we are going to talk about dietary fibre, which is the fibre found in foods.

What is dietary fibre?

It is defined as the organic residue of plant-based foods that is not hydrolysed by the digestive juices of the gastrointestinal tract and which can only be partially broken down in the large intestine.

Types of dietary fibre

Below, we list and explain the different forms of dietary fibre.

Soluble fibre

When in contact with water, it forms a mesh that traps water and gels the mixture, giving it the ability to absorb water and increase the volume of stools.

It is more extensively fermented in the colon. It also binds substances in the intestines, preventing their absorption – such as cholesterol. It slows the absorption of some nutrients like glucose and increases the time the stomach takes to empty.

It is found in legumes, most fruits, nuts and oilseeds, and seaweeds.

Insoluble fibre

It forms low-viscosity mixtures with water. It is barely fermented in the colon.

It has a greater laxative and intestinal regulating effect due to its ability to increase intestinal transit speed, supporting peristalsis.

Foods rich in this type of fibre include some cereals and legumes, and vegetables such as artichokes, spinach, Swiss chard, green beans, lettuce, carrot, and raw tomato.

Main components of dietary fibre

Polysaccharides

• Cellulose: A glucose polymer found in the outer layer of cereals and in vegetables such as artichokes, spinach, and green beans.
• Hemicelluloses: Found in the same foods as cellulose. They are not digested in the human small intestine, although they are partially broken down in the colon by microbial flora.
• Pectins: Found in the soft tissues of fruits. They have the ability to form gels in the presence of sugar, heat, and a mildly acidic medium. Used to thicken some jams and preserves.
• Gums and mucilages: Water-soluble polysaccharides with a high capacity to retain water. These include guar gum and the husk of *Plantago Ovata*.

Carbohydrate analogues

• Indigestible dextrins
• Resistant maltodextrins
• Polydextrose
• Methylcellulose
• Resistant starch
• Non-synthetic carbohydrates
• Hydroxypropylmethylcellulose

Oligosaccharides

• Inulin
• Fructooligosaccharides (FOS)
• Galactooligosaccharides (GOS)

Non-carbohydrate derivatives

• Lignin: Forms the structure of the toughest or most woody parts of vegetables such as Swiss chard, lettuce, cereal husks, etc. It is completely indigestible.
• Waxes
• Phytates
• Cutins and suberins
• Polyphenolic compounds (tannins)

Functions of fibre

1. Fibre-rich foods generally increase satiety value, meaning they make a person feel “full” and increase gastric emptying time, thus delaying the sensation of hunger after meals.
2. They increase the volume and weight of stools and reduce intestinal transit time.
3. They reduce blood cholesterol levels.
4. They have a prebiotic effect – meaning some types of fibre are fermented by the colon flora and support the proliferation of probiotic bacteria.
5. They also reduce postprandial glucose and insulin levels.
6. They reduce the absorption of carbohydrates, fats, and proteins due to the gel layer formed around intestinal contents.

Fibre recommendations

Recommended fibre intake ranges from 26 to 38 grams per day. These levels are not met in Spain, where, according to surveys (ENIDE), the intake ranges from 17–21 grams per day.

Low fibre consumption is associated with a higher incidence of diseases such as constipation, diverticulosis, diabetes, obesity, hypercholesterolaemia, cardiovascular risk, inflammatory bowel disease, and some types of cancer (colon and breast).

How to increase fibre intake

In the attached table, you will find foods with the highest fibre content (Novartis, ed. 2000).

Increase your intake of fruit and vegetables, wholegrain cereals – and by this I don’t mean sugary breakfast cereals – switch from white bread to wholemeal, and opt for wholegrain rice and pasta too. Include nuts and legumes in your diet.

These are in fact small changes that you’ll hardly notice, but they will bring you great health benefits.