Need in dietary fibres
What are they ?
Dietary fibres are long chains carbohydrates (ten or more sugar units) that are not digested nor absorbed in the small intestine. They are partially or completely fermented by microorganisms in the large intestine.
They are either naturally occurring in food or transformed by processing, or even synthesized to be added to food to provide a health benefit.
Why do we need fibres?
Some fibres are soluble in water and generally become viscous, like fruit pectin that thickens gellies, some others are insoluble and have a very low viscosity or are not viscous at all, like cellulose from wheat bran for example. The level of viscosity determines their biological properties.
Fibres can help maintain a good health by different mechanisms:
- They take a lot of volume in the stomach, particularly soluble fibers that absorb water and swell; therefore they decrease the quantity of other calorie-rich foods we can eat.
- They slow down the food transit in the upper digestive system, increasing the sensation of fullness, helping eating less.
- They provide only an average of 2 kilocalories per gram, so it accounts for a lower calorie intake as compared to other macronutrients such as fat, sugar and protein.
- They slow down the digestion and absorption of carbohydrates and fat, helping the regulation of blood glucose and blood cholesterol. The role of soluble fibres in the reduction of cardiovascular diseases risk through their action on blood cholesterol is quite well established, particularly if they are associated with a diet low in saturated fat.
- They increase stool weight; stool weight is further increased by the mass of bacteria that ferment fibres in the colon. This fermentation produces short chain fatty acids (SCFAs) that have beneficial effects on health.
- Soluble fibres prevent constipation and bacterial infection of the appendix by keeping the intestinal content moist and insoluble fibres accelerate the intestinal transit. They reduce the risk of diverticulitis and they are thought to help reduce the risk of colon cancer.
What are the sources of fibres?
Vegetables, legumes (pulses), fruits, whole grains and nuts are the sources of fibre in our diet.
How much do we need?
The recommendations are to eat at least 25 g of fibre per day, which is quite difficult to achieve.
A portion of most fruits and vegetable contain between 2 and 4 g of fibre. Legumes contain more, between 6 and 8 g per portion and one slice of wholemeal bread contains 2-3 g of fibre.
It is therefore very important to eat the recommended 5 portions of fruits and vegetable per day as well as legumes and grains.
Did you know that pop-corn is a good source of fibre, because it still has the grain envelope? But beware of what you put on them!
ILSI EUROPE CONCISE MONOGRAPH SERIES, DIETARY FIBRE (2006)
Dietary fibre intake and risk of cardiovascular disease: systematic review and meta-analysis.D E Threapleton et al, British Medical Journal 2013, 347:68-79