Definition and Classification
Carbs, also called carbohydrates (from the Greek “glucos” = sweet) are substances formed by carbon and water. They have a molecular form (CH2O)n and are mainly contained in food of plant origin.
On average they provide 4 kcal per gram, although their energy value ranges from 3.74 kcal of glucose to 4.2 kcal of starch. Of these calories about 10% is used by the body for digestion and absorption processes.
Depending on their chemical structure, carbs are classified into simple and complex carbohydrates.
Simple carbs, commonly called sugars, include monosaccharides, disaccharides and oligosaccharides.
In nature there are more than 200 monosaccharides that differ in the number of carbon atoms in their chain.
Hexoses (fructose, glucose, galactose) are the most important from a nutritional point of view.
Is normally found in food, either in free form or as a polysaccharide. It is the form in which other sugars must be transformed in order to be used by our organism.
Only 5% of the total amount of carbohydrates present in our body is represented by glucose circulating in the blood. Glycemic index = 100.
Is found in abundance in fruit and honey; it is absorbed in the small intestine and metabolized by the liver which transforms it into glucose. Its glycemic index is very low, equal to 23.
In nature is not found free but bound to glucose forms lactose, the sugar of milk.
Are formed by the union of two or more monosaccharides (maximum 10). They are found mainly in vegetables and in particular in legumes.
The most well-known, as they are nutritionally important, are the disaccharides (sucrose, lactose and maltose).
Glucose+fructose; very common it is present in honey, beets and sugar cane.
Its glycemic index is 68 ? 5
Glucose + galactose; it is the milk, sugar and the least sweet among the disaccharides.
Its glycemic index is 46 ? 6.
Glucose+glucose; A little present in our diet is mainly found in beer, cereals and sprouts.
Its glycemic index is 109.
Among the oligosaccharides are maltodextrins.
Maltodextrins are oligosaccharides derived from the hydrolysis process of starches.
They are used as energy supplements and can be useful in endurance sports.
They provide energy in the short and medium term without straining the digestive system too much.
Polysaccharides are formed by the union of numerous monosaccharides (10 to thousands) through glycosidic bonds.
We make a distinction between vegetable polysaccharides (starches and fibres) and polysaccharides of animal origin (glycogen).
Polysaccharides containing only one type of sugar are called homopolysaccharide, while those containing different types of monosaccharides are called heteropolysaccharide.
Is the carbohydrate reserve of vegetables. It abounds in seeds and cereals; it is also found in enormous quantities in peas, beans and sweet potatoes. In nature it is present in two forms, amylose and amylopectin. The higher the amylopectin content, the more digestible the food is.
Are structural polysaccharides, the most important of which is cellulose.
Our body cannot use them for energy purposes, but their fermentation at intestinal level is essential to regulate the absorption of nutrients and to protect our body from many diseases.
They are divided into water-soluble and non water-soluble. The first chelates interfere with the absorption of nutrients, including cholesterol, the second attract water by accelerating gastric emptying.
The caloric contribution of fibre in the diet is zero.
Is a polysaccharide similar to amylopectin used as a source of deposit and primary energy reserve.
It is stored in the liver and muscles up to a maximum of 400-500 grams.
The glycogen present in animals is almost completely degraded at slaughter, so it is present in small amounts in food.
Digestion and absorption of carbohydrates
The digestion of carbohydrates begins in the mouth where the enzymes in the saliva begin the breakdown of complex carbohydrates.
In the stomach the action of salivary enzymes is interrupted by the acidic environment and resumes in the small intestine where, thanks to pancreatic juices (?-amylase enzyme), polysaccharides are reduced to monosaccharides.
While glucose is absorbed rapidly (both by osmotic gradient and by active transport), fructose is absorbed more slowly, through a facilitated diffusion mechanism, which is at the base of its low glycemic index.
If you liked our article on carbs, we recommend the article on proteins