They provide 4 kcal/gram as protein and energy are considered macronutrients like fat. We can find them in a countless number and variety of food and play an important role in metabolism. So they must have a strong presence in our daily diet.

In a varied and balanced diet approximately 300gr./día carbohydrates should come from fruits and vegetables, which not only provide us with carbohydrates, but we also provide vitamins, minerals and plenty of plant fibers.
Another 50 to 100 g. newspapers must be complex, ie cereals and their derivatives. Always prefer those grains which retain their bark, grains. They are rich in B vitamins, minerals, vegetable proteins and obviously fiber.

The fiber should always be present in an amount of 30 gr. daily, thereby preventing weight disorders and diseases such as obesity.
In all low-calorie diets in fruit and vegetables are helpful because they provide plenty of nutrients without too many calories.

Functions
The functions of carbohydrates in the body are met, energy saving proteins, regulate fat metabolism and structure.
* Drink tap, carbohydrates provide 4 kcal (kilocalories) per gram dry weight. This is without considering the content of water that might have the food which is carbohydrate. Covers energy needs, a small part is stored in the liver and muscles as glycogen (usually no more than 0.5% by weight of the individual), the rest is converted into fat and accumulates in the body as adipose tissue.
It is generally recommended that minimally effected a daily intake of 100 grams of carbohydrates to maintain metabolic processes.
* Savings of proteins: If carbohydrate intake is insufficient, protein is used for energy purposes, relegating their plastic function.
* Regulation of fat metabolism: In case of poor dietary intake of carbohydrates, fats are metabolized abnormally accumulate in the body ketone bodies, which are intermediate products of this metabolism thus causing problems (ketosis).
* Structurally, the carbohydrates are a small portion of the weight and structure of the body, but either way, this function should not be excluded from the list, however minimal its indispensable contribution.

Classification of carbohydrates:
* The simple:
Simple carbohydrates are monosaccharides, among which we mention the glucose and fructose which are responsible for the sweet taste of many fruits.
With these simple sugars should be careful because they have great taste and quickly absorbed by the body. Its absorption leads to our bodies secrete insulin hormone that stimulates appetite and promotes fat deposition.

Sugar, honey, maple syrup (maple syrup), jams, jellies and sweets are simple carbohydrates and easily absorbed.
Other foods such as milk, fruits and vegetables contain even distributed over a larger amount of water.

Something to keep in mind is that industrial products prepared from refined sugars is that they have a high calorific and low nutritional value, so that their consumption should be moderate.

* Complex:
Complex carbohydrates are polysaccharides, complex forms of multiple molecules. These include cellulose that forms the wall and the support of the plants, the starch in the potato tubers and glycogen in muscle and liver of animals.

The body uses the energy from complex carbohydrates by little, so they are slow absorption. They are found in breads, pasta, cereals, rice, beans, corn, barley, rye, oats, etc..

Digestion of carbohydrates
To know how is the metabolism of carbohydrates, see how is your digestion.

Referring to the basic biochemistry of Carbohydrates, we can say that carbohydrates are polihidroxicetonas or polihidroxialdehidos and its derivatives. For the purposes of study in nutrition takes into account only those with four or more carbon atoms.
These compounds are highly polar and are joined together giving polymers.