Carbohydrates

Molecules of all monosaccharides contain atoms of carbon, hydrogen and oxygen in the same proportion. Their chemical formula is: CnH2nOn, where n is a positive integer number. But even monosaccharides with the same formula (the same n) substantially differ by their structure and vary in the spatial structure of their molecules. For instance, formulas of glucose, fructose and to galactose are the same – C6H12O6, but these are completely different substances (even though all three are sweet). 

There are also other monosaccharides. Among them, the most common in living creatures (including plants) are ribose (the "backbone" of the ribonucleic acid – RNA) and deoxyribose (the "backbone" of deoxyribonucleic acid – DNA). One molecule of ribose is also included in the core of the ATP molecule. We get ribose and deoxyribose from food, because a considerable part of our food consists of biological cells, which contain their genetic code (RNA and DNA), but also we can produce molecules of ribose and deoxyribose out of glucose. We need these molecules for building copies of our own molecules of the genetic code.

Disaccharides are substances, molecules of which are made of two molecules of monosaccharides. The most common disaccharides:

●  Sucrose is made of a molecule of glucose and a molecule of fructose. Sugar is made of molecules of sucrose.
●  Lactose is made of a molecule of glucose and a molecule of galactose. This is the "milk sugar", it gives a slight sweetness to milk.
●  Maltose is made of two molecules of glucose. It is the "malt sugar". It is present in malt, where it is a product of fermentation of starch that is present in grains of certain cereals when they are sprouted for manufacturing malt.

When we consume disaccharides with food, they are split by special enzymes into monosaccharides. This process begins in the mouth and continues in the stomach.

Polysaccharides are carbohydrates composed of a large number of monosaccharides. Most commonly with our food we consume polysaccharides composed of many molecules of glucose.

● Starch. 

This polysaccharide is produced by almost all plants for storing energy for the time when obtaining energy from the sun is impossible (night) or limited (cloudy weather), Or when the plants don't have leaves (in winter). Also starch is deposited in grains and seeds of plants as a storage of energy for the springs of the new plants. Starch makes 90% or more of the grains of wheat, rye, oats, barley, rice, corn and other cereals, and also in potatoes, and somewhat less than 90% In a legumes -beans, kidney beans, peas and lentils. It is also present in beetroots, carrots, cabbage, fruits, berries and generally in all plants which we consume as food.

A molecule of starch is a chain of glucose molecules. This chain can be unbranched (amylose) or branched (amylopectin). Amylose makes About a quarter of natural starch, and amylopectin – about three quarters.

When we consume start with food, we excrete a special enzyme, which breaks starch into separate molecules of glucose. This process begins in the mouth when we chew the food and continues in the stomach and even in the intestines. From the intestines, glucose gets into our blood. 

Food that contains almost nothing but easily the digestible starch (for instance, boiled potatoes) increases the blood glucose level even stronger than sugar, because sugar contains only 50% of glucose. But this does not mean that potatoes are more “harmful” then sugar.

The remaining 50% of sugar is fructose, which has many negative influences on our organism, if it is consumed in the pure form (and not as a part of the whole fresh fruits with fiber). And the generally, glucose as such is not harmful, and therefore neither is starch. Only their excessive and frequent consumption is harmful.

● Glycogen. 

Glycogen is an animal analog of starch, that is, it is a polysaccharide composed of molecules of glucose. Its purpose is the same as that of starch – to store energy. Formation of a large glycogen molecule is initiated by a special protein – glycogenin. 

We can obtain some amount of glycogen by eating meat, because glycogen is accumulated in muscles and the liver. But its amount in meat food is much smaller than the amount of starch in plants.

We form our own glycogen out of molecules of glucose that we obtain from carbohydrates consumed with food or is produced out of fats or amino acids by our liver. We accumulate glycogen mostly in muscles and the liver. But we can store only a limited amount of glycogen. The excess of glucose that cannot be converted into glycogen for storage is converted by our liver into fats, which are then accumulated in the fat tissue.

● Fiber. 

This is a large group of substances, which form walls of living cells of plants and their mechanical structure – trunks and bark of trees, stems of other plants, etc. Therefore, fiber is present in any plant food, but in different quantities and proportions. 

Like in starch, molecules of fiber are also chains of glucose molecules, branched or unbranched. But, unlike in starch, fiber molecules are larger, and molecules of glucose in them are connected with stronger bonds. Therefore, those enzymes that break up starch molecules, cannot break fiber molecules. Thus, fiber is not a source of energy for us. Despite this, fiber is a very important component of our food. It is not food for us, but it is food for useful bacteria that live in our intestines. And also it forms the mass, which can be pushed by the intestines alongside themselves, ensuring absorption of various nutrients in exactly those parts of the intestines that are intended for absorbing these nutrients. This, on the one hand, slows down absorption of food (and gives us a longer time when we do not want to eat again), and, on the other hand, makes the absorption more efficient. In particular, fiber slows down absorption of glucose and ensures delivery of a considerable part of fructose to those parts of the intestines, where it can be consumed by useful bacteria). 

There is fiber that is soluble, and there is fiber that is insoluble.

Soluble fiber. Its molecules do not dissolve like, for instance, molecules of salt. They remain whole and surround themselves with molecules of water, owing to which than can "float" in water rather than precipitate to the bottom. Mostly, this is pectin. At a sufficient concentration, these molecules can form a jelly-like mass similar to marmalade. 

Insoluble fiber. Its molecules do not mix with water and are usually bound with each other to form long and rather hard of different size, mostly in the form of fibers. Mostly this is cellulose. Yes, the same as in wood, from which paper is made, but in the plants we eat, these fibers are shorter, and they are not tied to each other in the plants we eat than they are in the wood.

● Other polysaccharides. 

Polysaccharides can be formed not only out of glucose. For instance, there is galactogen – a polysaccharide similar to glycogen, which is used by some species of snails for storing energy, just like we use glycogen for this purpose. Galactogen is composed of a large number of molecules of galactose. 

There are also heteropolysaccharides, which are formed of chains of different monosaccharides, unlike molecules of starch, fiber and galactogen composed of molecules of only one monosaccharide, and for this reason they are called homopolysaccharides.