Carbohydrates, also called carbohydrates (from the Greek "glucos" = sweet) are substances formed by carbon and water and are mainly contained in foods of vegetable origin. The food group that contains them in greater quantities is that of cereals.

Carbohydrates play a fundamental role in human nutrition as they represent the main source of energy for the body. On average they provide 4 kcal per gram, even if their energy value varies from 3.74 kcal of glucose to 4.2 Kcal of starch.

Based on their chemical structure, carbohydrates can be classified into simple and complex.

Simple carbohydrates (or carbohydrates), commonly called sugars, include:

  • monosaccharides, with a very simple chemical structure, such as glucose, fructose and galactose
  • disaccharides, formed by the union of two monosaccharides, such as sucrose (glucose + fructose), lactose (glucose + galactose) and maltose (glucose + glucose)
  • oligosaccharides, consisting of two to ten molecules of monosaccharides, such as maltodextrins (usually used as energy supplements)

In nature there are hundreds of monosaccharides which differ in the number of carbon atoms present in their chain.However, those formed by six carbon atoms (the hexoses) such as fructose, glucose and galactose, are the most important from a nutritional point of view. Among all, the one of greatest interest is glucose, which is the form in which the other sugars must be transformed in order to be used by our body.

Complex carbohydrates (or carbohydrates) can also be defined as polysaccharides, since they are formed by the union of numerous (from ten to thousands) molecules of monosaccharides. They are divided into polysaccharides of vegetable origin (starches and fibers) and polysaccharides of animal origin (glycogen, reserve of carbohydrates in the muscle, which is used during physical activity).


There are three main categories of carbohydrates in food:

  • sugars, simple carbohydrates found naturally in fruits, vegetables, milk and dairy products. The most common sugars are fruit sugar (fructose), table sugar (sucrose) and milk sugar (lactose)
  • starch, complex carbohydrate consisting of many sugar units bound together. Starch is found naturally in cereals, potatoes and legumes. In nature it is present in two forms, amylose and amylopectin. Usually the higher the amylopectin content than amylose, the more digestible the food is
  • fibers, complex carbohydrates that our body is unable to use for energy purposes, but whose fermentation in the intestine by the bacterial flora is essential to regulate the absorption and passage of nutrients and to protect our body from numerous pathologies. They occur naturally in fruits, vegetables, whole grains and legumes

Nutritional indications

According to the Guidelines for Proper Nutrition, 45-60% of daily calories should come from carbohydrates, at least three-quarters in the form of complex carbohydrates and no more than 10% in the form of simple sugars.

The importance of carbohydrates derives from the fact that they are absorbed and used by the body very easily, ensuring the cells a supply of glucose and therefore of energy.

Starch, before being used to produce energy, must be transformed, during digestion, into glucose. Because of this it is absorbed more slowly and provides energy for a longer period of time.

Cereals are the basis of the Mediterranean diet and due to their intake of complex carbohydrates they should be consumed daily.

For a balanced diet and body weight control, it is important not to eliminate carbohydrates from your diet and be careful to consume them in portions appropriate to your body, age and physical activity.

Furthermore, attention must be paid not only to the quantity but also to their quality. Foods containing added sugars, such as sugary drinks, sweets and candies, should not be consumed frequently, preferring fruits, vegetables and whole grains instead.

Carbohydrate metabolism

During digestion, the sugars and starches contained in food are broken down into glucose which, absorbed by the intestine, passes into the bloodstream. From here, thanks to the action of the insulin produced by the pancreas, the glucose enters the cells of the body where it is used to produce energy.

Excess glucose is stored in the form of glycogen, in the liver and muscles, for later use or, if in excess, converted into fat.The sugar content in the blood is called blood sugar; different carbohydrates have a different ability to cause an increase in blood sugar when consumed; this property is expressed with the glycemic index. Many organs and tissues, such as the brain, are glucose-dependent, meaning they require glucose for their metabolic activities.

In the absence of carbohydrates, the liver is able to produce glucose from other sources, such as proteins and fats, using a metabolic pathway called gluconeogenesis.

When the diet is low in carbohydrates, for example when following high-protein or ketogenic diets, energy is produced using storage fats and muscle proteins.

This leads to the formation of ketone bodies which are used by the brain to meet its own energy needs. However, if carbohydrate deficiency continues for too long, the production of ketone bodies becomes excessive and can pose a health risk.

In-depth link

Council for Agricultural Research and Analysis of the Agricultural Economy (CREA). Guidelines for healthy eating 2018

Italian Society of Human Nutrition (SINU). LARN 2014: Reference levels of nutrient and energy intake for the Italian population. Quantitative portion standards. 2014; IV revision

Mayo Clinic. Carbohydrates: How carbs fit into a healthy diet (English)

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