In addition to absorbing nutrients, the gut’s primary function is to excrete undigested food debris. In order for anything superfluous to be removed from the intestines, we need fiber. It is a substance most often of plant origin, which includes, among others cellulose, lignin or hemicellulose, as well as pectin and mucilage.
What is characteristic and important – fiber is not digestible. It passes through the digestive system to the large intestine so that all debris can be removed with it – i.e. products of the digestive process that have not been absorbed somewhere along the way. And it is fiber that is one of the main components of stool – the final form of chyme.
We often only think about the importance of fiber when we become constipated. Eating high-fiber foods is the best way to prevent them. Its most important sources are plants – i.e. vegetables and fruits (not juices!) – and cereal products, especially whole grain or wholemeal bread, groats, cereals and rice. In special cases – e.g. in diseases that impair the ability to digest or assimilate certain foods – the doctor may order fiber supplementation through preparations containing it.
It should be remembered that excess fiber can also be harmful and cause insufficient absorption of fats, which in turn has an effect on the absorption of vitamins soluble in them. American nutritionists4 in official guides recommend the consumption of about 25 g (women) and 38 g (men) of fiber per day.