Carbohydrates are molecules made up by carbon, hydrogen and oxygen; everyone has different composition of them. We found in the nature: Monosaccharaides, Disaccharides and Polysaccharides.
MONOSACCHARIDES. Glucose, Fructose, Galactose.
Glucose. We found it in animal and vegetables tissues. Our cells use it to get energy. Some of our cells can use another source of energy but kidney cells, medullary cells, cerebral cells and red blood cells cannot. They just can use glucose.
Honey and fruits contains glucose freely, in other food appears combining with other molecules.
Fructose. Fruits, vegetables and honey contain fructose freely. Fructose + glucose = saccharose (what we know as table sugar.
Galactose. It always combines with other molecules, we cannot find at nature freely. Glucose + galactose = lactose.
DISACHARIDES. Made up by two monosaccharaides, one of them is always glucose.
Saccharose. Glucose + fructose. Table sugar.
Lactose. Glucose + galactose. It's milk mammal’s sugar. When it arrives at gut (small intestine, specifically), there is a molecule that hydrolyzes (chemical process) the lactose. This molecule is called lactase. The more you ingest lactose, the more you synthesize lactase.
If your body doesn’t produce lactase, you cannot assimilate lactose, the bacteria in your colon cause fermentation. It can makes you feel flatulencies, diarrhea and physical discomfort (at different levels). This is called Lactose Intolerance.
Maltose. Glucose + glucose. It's in some vegetables, but especially in cereals.
POLYSACCHARIDES. They are carbohydrates formed by 10 or more monosaccharaides (from 2 monosaccharaides from 10 they are called oligosaccharides).
Starch. The way that vegetables keep carbohydrates, reserve them. We found starch in cereals, tubers and legumes. The last molecule of its digestion is glucose.
Glycogen. The way the animals (never vegetables) keep carbohydrates, reserve them to use when necessary (for example between meals). The reserve it's in liver and muscles. The last molecule of its digestion is also glucose.
Our body obtains glucose from our liver "store" (glycogen), this happens during the period between meals. When it's ended, our body will use fatty acids to obtain glucose. When it is also ended, the muscle "store" will be the last source of glucose (this happens when undernourishment; our body needs too much energy to use the glucose in the muscle, this is why it just happens when extreme situations).
You should know...
When we talk about fast absorption carbohydrates, we are talking about what we call "simple sugars" they are monosaccharaides and disaccharides. When we talk about slow absorption carbohydrates, it means polysaccharides (we called them "complex sugar").
The first ones are those that make glucose rises in blood, quickly. If you eat them in excess glucose intolerance can appear easily, even diabetes.
As you know, monosaccharaides and disaccharides are: white sugar, honey, brown sugar and fruits (overall mature fruits. They contain more monosaccharaides). And factory-baked goods, these are the worst concerning monosaccharaides as sugar.
The recommendation of carbohydrates intake per day is 50-55% of the total intake per day. 10% of these should come from "simple sugars", this means from table sugar, honey, milk (lactose). The remaining (40-45%) should come from polysaccharides: cereals, tubers, legumes, and some vegetables. This is what a dietitian/nutritionist work out.
In general, the Mediterranean alimentation covers these needs. In every meal there are a plate of polysaccharides (cereals, bread, pasta, rice...), tubers (sweet potato, potato...) or legumes (lentils, pea, chickpea...). Plus the sugar, honey or lactose you take per day.
1. Energy, mainly. They are essential to bring about muscular contraction. They are the basis of our daily energetic expenses.
2. Reserve. As you know, we ate food and we obtain glucose. This glucose will be consumed or accumulate in our "store" (liver, muscle, fat). Remember during the period between meals, you will use this "store".
If you eat more carbohydrates than your organism needs, you will full your "store". And if you eat more than the "store" can keep, these carbohydrates will transform to triglycerides. I'm sure you listen that carbohydrate makes you put on weight. Well, this is true if you eat more that you need. If you have a balanced diet, they shouldn't make you gain weight.
3. Carbohydrates are part of some molecular structures as DNA or ATP.
Now, it's your turn... if you have any doubt, suggestion, whatever you need, you can contact me. I'll be happy to "read you".