For our body, carbohydrates are one of the key sources of energy. Today we look at the types and functions of carbohydrates, and also find out what foods they contain.
Why does a person need carbohydrates?
Before considering the types of carbohydrates, we will understand their functions. In the human body there is always a carbohydrate reserve in the form of glycogen. It is about 0.5 kg. 2/3 of this substance is in muscle tissue, and another third - in the liver. Between meals, glycogen breaks down into glucose, thereby leveling out fluctuations in blood sugar.
Without the intake of carbohydrates, glycogen reserves end in 12-18 hours. If this happens, carbohydrates begin to form from the intermediate products of protein metabolism. These substances are vital for humans, since they, mainly due to the oxidation of glucose, form energy in our tissues.
Deficit
With chronic carbohydrate deficiency, the glycogen supply in the liver is depleted, and fats begin to be deposited in its cells. This leads to the degeneration of the liver and a violation of its functions. When a person consumes an insufficient amount of carbohydrates with food, his organs and tissues begin to use not only protein, but also fat for energy synthesis. Increased fat breakdown leads to metabolic disorders. The reason for this is the accelerated formation of ketones (the most famous of them is acetone) and their accumulation in the body. When ketones are formed in excess, the internal environment of the body “acidifies”, and brain tissue gradually begins to poison.
Excess
Like a deficiency, an excess of carbohydrates does not bode well for the body. If a person takes too much carbohydrate with food, the level of insulin and glucose in the blood rises. As a result, fat deposits form. It happens as follows. When a person does not eat all day after breakfast, and in the evening, having come home from work, decides to take lunch, afternoon snack and dinner at the same time, the body tries to fight with an excess of carbohydrates. So there is an increase in blood sugar. For glucose to pass from the blood to tissue cells, insulin is needed. He, in turn, getting into the blood, gives an incentive to the synthesis of fats.
In addition to insulin, other hormones regulate the metabolism of carbohydrates. Glucocorticoids are hormones of the adrenal cortex that stimulate the synthesis of glucose from amino acids in the liver. The same process is enhanced by the hormone glucagon. In function, glucocorticoids and glucagon are opposite to insulin.
Norm
According to the norms, carbohydrates should make up 50-60% of the calorie content of food. It is impossible to exclude them from the diet, despite the fact that they are partly “guilty” in the formation of extra pounds.
Carbohydrates: types, properties
According to their chemical structure, carbohydrates are divided into simple and complex. The former include mono- and disaccharides, and the latter include polysaccharides. We analyze both classes of substances in more detail.
Simple carbohydrates
Glucose We begin to consider simple types of carbohydrates from the most important of them. Glucose acts as a structural unit of the bulk of poly- and disaccharides. During metabolism, it breaks down into monosaccharide molecules. They, in turn, during a complex reaction turn into substances that are oxidized to water and carbon dioxide, which are fuel for cells.
Glucose is an important component in carbohydrate metabolism. When his blood level drops or a high concentration makes normal functioning of the body impossible (as in the case of diabetes), a person experiences drowsiness and may lose consciousness (hypoglycemic coma).
In its pure form, glucose (as a monosaccharide) is found in a large number of vegetables and fruits. Especially this fruit is rich in such fruits:
- grapes - 7.8%;
- cherries and cherries - 5.5%;
- raspberries - 3.9%;
- strawberries - 2.7%;
- watermelon and plum - 2.5%.
Among vegetables rich in glucose, it can be noted: pumpkin, cabbage and carrots. They contain about 2.5% of this component.
Fructose . This is one of the most common fruit carbohydrates. It, unlike glucose, can penetrate from the blood into tissues without the participation of insulin. Therefore, fructose is considered the optimal source of carbohydrates for people with diabetes. Part of it enters the liver, where it turns into glucose - a more versatile “fuel”. Such a substance can also increase blood sugar, but not as much as other simple carbohydrates. Fructose is converted to fat more easily than glucose. But its main advantage is that it is 2.5 and 1.7 times sweeter than glucose and sucrose, respectively. Therefore, this carbohydrate is used instead of sugar in order to reduce the calorie content of food.
Most fructose is found in fruits, namely:
- grapes - 7.7%;
- apples - 5.5%;
- pears - 5.2%;
- cherries and cherries - 4.5%;
- watermelons - 4.3%;
- blackcurrant - 4.2%;
- raspberries - 3.9%;
- strawberries - 2.4%;
- melon - 2.0%.
Fructose contains less in vegetables. Most of all it can be found in white cabbage. In addition, fructose is present in honey - about 3.7%. It is authentically known that it does not cause caries.
Galactose . Considering the types of carbohydrates, we have already become acquainted with some simple substances that can be found in products in a free form. Galactose is not such. It forms a disaccharide with glucose called lactose (aka milk sugar) - the main carbohydrate in milk and products derived from it.
In the gastrointestinal tract, lactose is split into glucose and galactose by the action of the enzyme lactase. Some people have milk intolerance associated with a lack of lactase in the body. Unsplit, lactose is a good nutrient for intestinal microflora. In fermented milk products, the lion's share of this substance is fermented to lactic acid. Due to this, people who have lactase deficiency can use fermented milk products without unpleasant consequences. In addition, they have lactic acid bacteria that inhibit the activity of intestinal microflora and neutralize the effects of lactose.
Galactose, the formation of which occurs during the breakdown of lactose, in the liver turns into glucose. If a person lacks the enzyme that is responsible for this process, he may develop a disease such as galactosemia. Cow's milk contains 4.7% of lactose, in cottage cheese - 1.8-2.8%, in sour cream - 2.6-3.1%, in kefir - 3.8-5.1%, in yoghurts - about 3%
Sucrose. On this substance, we will finish considering simple types of carbohydrates. Sucrose is a disaccharide that consists of glucose and fructose. Sugar contains 99.5% sucrose. Sugar is rapidly broken down by the gastrointestinal tract. Glucose with fructose is absorbed into human blood and serves not only as a source of energy, but also the most important glycogen precursor in fat. Since sugar is pure carbohydrates that do not contain nutrients, many call it the source of “empty calories”.
Beetroot is the richest sucrose product (8.6%). Among other plant fruits, one can distinguish peach - 6%, melon - 5.9%, plum - 4.8%, mandarin - 4.5%, carrots - 3.5%. In other vegetables and fruits, the sucrose content varies between 0.4-0.7%.
A few words should also be said about maltose . This carbohydrate consists of two glucose molecules. Maltose (malt sugar) is found in honey, molasses, confectionery, malt and beer.
Complex carbohydrates
Now discuss the types of complex carbohydrates. These are all polysaccharides that are found in the human diet. With rare exceptions, glucose polymers can be found among them.
Starch . This is the main carbohydrate digested by humans. It accounts for 80% of carbohydrates consumed with food. Starch is found in potatoes and cereal products, namely: cereals, flour, bread. Most of this substance can be found in rice - 70% and buckwheat - 60%. Among cereals, the lowest starch content is observed in oatmeal - 49%. Pasta contains up to 68% of this carbohydrate. In wheat bread, starch is 30-50%, and in rye, 33-49%. This carbohydrate is also found in legumes - 40-44%. Potatoes contain up to 18% starch, so nutritionists sometimes attribute it not to vegetables, but to starchy foods, like cereals with legumes.
Inulin . This polysaccharide is a polymer of fructose, which is found in Jerusalem artichoke and to a lesser extent in other plants. Products containing inulin are prescribed for diabetes and its prevention.
Glycogen It is often called "animal starch." It consists of branched glucose molecules and is found in animal products, namely: liver - up to 10% and meat - up to 1%.
Conclusion
Today we examined the main types of carbohydrates and found out what functions they perform. Now our approach to nutrition will be more meaningful. A brief summary of the above:
- Carbohydrates are an important source of energy for humans.
- Their excess is as bad as its lack.
- Types of carbohydrates: simple, complex.
- Mono and disaccharides are simple, and polysaccharides are complex.