Edited by Dr. Davide Marciano
Carbohydrates are the primary fuel of the human machine. Their main task is the production of energy, which is essential for the vital processes of the organism.
From a chemical point of view they are made up of Carbon, Hydrogen and Oxygen in the ratio 1: 2: 1.
Based on their constitution and absorption, they are divided into:
MONOSACCHARIDES, carbohydrates with a single sugar molecule (glucose, fructose, galactose),
DEACCHARIDS, carbohydrates with two sugar molecules (maltose, lactose and sucrose)
POLYSACCHARIDES, carbohydrates with 3 or more sugar molecules (starches, glycogen and fiber).
Monosaccharides and disaccharides are called sugars or simple carbohydrates.
Polysaccharides, on the other hand, are called complex carbohydrates or glucose polymers.
They are stored in the form of glycogen in the muscles (fuel reserve for the synthesis of ATP necessary for muscle activity) and in the liver (glucose reserve for maintaining blood levels of this sugar).
The body, in resting conditions, consumes 160g of glucose per day, of which 120g is used by the brain (this is one of the reasons why you should never consume less than 160g of carbohydrates per day).
Simple carbohydrates
For the purpose of our discussion, the most important monosaccharides are glucose, also called dextrose, and fructose or fruit sugar (only ripe fruit is rich in this sugar).
These two monosaccharides like all other carbohydrates differ according to the speed of absorption. Each food has been assigned a Glycemic Index (GI) which corresponds to the speed with which carbohydrates arrive in the bloodstream.
Carbohydrates with a high glycemic index, such as dextrose, are quickly used for energy purposes even if what happens is totally the opposite.
In fact, carbohydrates with a high glycemic index induce an immediate influx of sugars into the blood, raising blood sugar levels; the sudden increase in the latter stimulates the release of insulin which carries glucose away from the bloodstream, thus causing energy levels to drop.
Complex carbohydrates
The polysaccharides, as we have already said, are:
- Starch is the form in which plants store their carbohydrates, in fact we find it in cereals and vegetables, especially potatoes.
- Glycogen is the form in which animals store glucose.
- Cellulose, finally, is a particular type of carbohydrate which constitutes the physical structure of a plant. Man, however, is unable to use it as an energy source because our digestive system is unable to break the bonds of this polysaccharide.
Cellulose, however, is very important as FIBER. It plays a fundamental role in the diet thanks to the "supply of bran. The latter" promotes an efficient functioning of the intestine and contributes to the passage of sugars into the blood stream. In addition, dietary fiber serves to soften the stool and to favor a normal elimination, also giving a greater sense of satiety.
Absorption of carbohydrates
In the small intestine, all carbohydrates are broken down into monosaccharides: glucose, fructose, galactose, levulose.
In this way they are able to pass through the intestinal walls. These nutrients are then transported to the liver, where all the monosaccharides are converted into glucose.
In fact, all carbohydrates to be assimilated are broken down into glucose.
The liver can use glucose by storing it internally as glycogen, or it can return it to the bloodstream for use as an energy source.
When there is more glucose in the body than is needed for immediate energy, the body converts this surplus amount into muscle glycogen.
Only after the glycogen stores are restored does the body take the remaining glucose from the blood and store it as fat.
Carbohydrates also contribute to the metabolization of proteins and to the elimination of nitrogenous waste deriving from the use of proteins.
They also have a fundamental role in the demolition of fats; always remember that "fats burn under the flame of carbohydrates".
