What are carbohydrates and what are they?
Among all the organic substances on our planet, carbohydrates are the most common, that is, they form the basis of life on the planet. A person eats simple carbohydrates (mono- and disaccharides: glucose, fructose, sucrose, lactose, etc.) and complex carbohydrates (polysaccharides), the chains of which consist of simple molecules. Polysaccharides are conventionally divided into digestible (for example, starch and inulin) and non-digestible (fiber).
Let's translate all this into a gastronomic plane: - simple carbohydrates are sugars contained in fruits and sweet vegetables, milk and, in fact, sweets - complex carbohydrates are found in cereals and flour products, nuts and legumes, vegetables, root vegetables - grain shells are rich in fiber, greens and some vegetables (zucchini, pumpkin, beets, carrots, etc.).
B Polysaccharides
Polysaccharides - or glycans - consist of monosaccharides linked together by glycosidic bonds.
Polysaccharides, unlike proteins and nucleic acids, form branched and linear polymer structures. This is due to the fact that glycosidic bonds can form between any hydroxyl groups of monosaccharides. Oligosaccharides containing three or more monosaccharide residues are relatively rare and are found most often in plant cells. Disaccharides, the simplest polysaccharides, are much more common. Many of them are formed during the breakdown of large polysaccharides.
The disaccharide lactose is contained in milk in a concentration of 0–7%. The most common disaccharide is sucrose (table sugar).
Rice. 1. Sucrose and lactose
Examples of structural polysaccharides are cellulose and chitin. The cell wall of plant cells contains cellulose as its main component. This allows plants to withstand significant differences in osmotic pressure between the extracellular and intracellular environments, up to 20 atm. Cellulose is a linear polymer of up to 15,000 D-glucose units linked together via β(1→4)-glycosidic bonds.
1.3Digestion of food carbohydrates
Digestion of carbohydrates occurs in the mouth and small intestine. Digestion occurs quite quickly and is catalyzed by the enzymes glycoside hydrolases (or glycosidases), which hydrolyze glycosidic bonds.
V. α-Salivary amylase;
d. α-Amylase of the pancreas.
Maltaza village; e. Sacrase;
The role of carbohydrates in the body
Once in the body, any carbohydrate is broken down into glucose. The body is not able to destroy it, and it simply passes through the gastrointestinal tract unchanged, simultaneously improving digestion. Glucose is a direct source of energy for the body. A special hormone, insulin, transports glucose to the tissues that need it, where it acts as “fuel.”
The body knows how to store glucose. It is built into glycogen chains, which are stored in the liver and muscles in case of prolonged hunger or physical activity. In addition, glucose is used to form other important carbohydrate compounds. For example, hyaluronic acid, which retains moisture in the skin tissue and promotes its elasticity. And also, so necessary for normal mobility and strength of joints - glucosamine, which is part of cartilage and intra-articular fluid.
Carbohydrate structures are also part of the mucus, which covers the walls of the nasopharynx, intestines, and reproductive organs, and protects them from damage and infections. Also, carbohydrates in the human body are involved in the regulation of blood thickness, in the construction of cell membranes and in the functioning of a number of hormones.
In addition, glucose is the only “fuel” for the brain. If other systems can use fats as an energy source, then our most important organ needs carbohydrates.
Physiology
The breakdown of complex carbohydrates in food begins in the oral cavity under the action of the enzymes amylase and maltase in saliva. The optimal activity of these enzymes occurs in an alkaline environment. Amylase breaks down starch and glycogen, and maltase breaks down maltose. In this case, lower molecular weight carbohydrates are formed - dextrins, and partially maltose and glucose.
In the stomach, the breakdown of food carbohydrates does not occur, since there are no specific enzymes for carbohydrate hydrolysis, and the acidic environment of gastric juice (pH 1.5-2.5) suppresses the activity of salivary enzymes. The main breakdown of dietary carbohydrates occurs in the small intestine. In the duodenum, under the action of the pancreatic juice amylase enzyme, complex carbohydrates are gradually broken down into disaccharides.
The main factors necessary for the breakdown of fat in the digestive tract are: the presence of enzymes that break down fats and the conditions for their optimal activity (pH); the presence of emulsifiers to transform fat into a finely crushed (emulsified) state. Such emulsifiers are bile acids (which are formed in the liver from cholesterol and enter the intestines with bile).
There are no necessary conditions in the oral cavity, so the chemical breakdown of fats does not occur. The stomach contains lipase with very low activity. This is due to the fact that the very acidic environment in the stomach (pH 1.5-2.5) suppresses the activity of lipase (pH 7.8-8.1), and there are no emulsifiers. Consequently, only already emulsified fats, which are contained in milk and egg yolk, can be broken down.
The main hydrolysis of neutral dietary fats occurs in the small intestine under the influence of active lipases. The environment in the intestines is slightly alkaline, i.e., optimal for the manifestation of lipase activity, which comes here with pancreatic juice.
Food proteins are not broken down in the oral cavity, since saliva does not contain hydrolytic enzymes.
The chemical breakdown of proteins begins in the stomach under the influence of proteolytic enzymes (peptide hydrolases), which break down peptide bonds between amino acids.
These enzymes are produced by the cells of the mucous membrane of the stomach, small intestine and pancreas in an inactive form. This form of enzymes prevents the self-digestion of proteins in the cells where they are synthesized and the walls of the gastrointestinal tract (especially for those who are still delusional about the fact that during fasting the stomach digests itself).
In the stomach, protein digestion occurs with the participation of the gastric juice enzyme pepsin, which is formed from inactive pepsinogen under the influence of hydrochloric acid. Pepsin exhibits maximum enzymatic activity in a strongly acidic environment at pH 1-2. In addition, under the influence of hydrochloric acid, swelling and partial denaturation of proteins occurs, which leads to an increase in the surface area of contact between the enzyme and proteins.
phenol, cresol, indole, hydrogen sulfide, mercaptans, etc. This transformation of amino acids in the large intestine is called protein putrefaction. Toxic substances are absorbed into the blood and delivered to the liver, where they are neutralized. The entire process of protein digestion in the gastrointestinal tract takes an average of 8-12 hours after eating.
What are the dangers of low-carb diets?
Considering the functions of carbohydrates in the body, their deficiency is fraught with unpleasant consequences: • a decrease in general immunity; • deterioration of digestion; • decreased cognitive functions (memory, concentration, reaction); • deterioration of emotional state; • menstrual cycle disorders in women; • increased fatigue.
With prolonged restriction of carbohydrates, the body can completely switch to using proteins and fats as “fuel”. When they break down, difficult-to-remove decomposition products are formed. Therefore, this diet is not suitable for everyone.
Many people know about the ability of carbohydrates to retain water. It is thanks to this that “carbohydrate-free” foods result in rapid weight loss. In the first few days, the liquid rapidly “drains”, which is accompanied by pleasant changes on the scales. But in the long term, this can impair overall tissue hydration, causing muscles and skin to become less elastic and therefore weaker and more susceptible to damage.
B Parietal digestion or hydrolysis by oligo- and disaccharidases
Oligosaccharides formed during the breakdown of polysaccharides by α-amylase and food disaccharides undergo further hydrolysis under the action of oligo- and disaccharidases built into the membranes of enterocytes. The products of this hydrolysis are monosaccharides, which are then transported across the membrane into the cytosol of enterocytes (this process is called absorption).
Oligosaccharidases are large glycoproteins (weighing over 200 kDa) that penetrate the enterocyte membrane. The active centers of these enzymes are directed
Excess carbohydrates
You also shouldn’t overdo it with “coals,” especially with simple ones. Abuse of them stimulates fermentation processes in the intestines, causing acne and allergies. It also promotes premature aging of the skin and internal organs.
Elevated blood glucose causes a sharp release of insulin. This hormone transports glucose where it is needed, but the body stores its excess as fat. If you exceed your recommended daily caloric intake from protein or fat, you will inevitably gain weight.
But carbohydrates are a little more insidious in the human body. Regular abuse of sugars leads to the fact that the sensitivity of cells to insulin decreases. As a result, the weight will be gained even faster, and it will be harder to lose. And if you continue to overload with carbohydrates, you can get diabetes.
Research has shown that people who overeat their caloric intake with carbohydrates are more likely to store belly and intra-abdominal fat. Those who exceeded the caloric intake of all nutrients equally showed a more even distribution of body fat. A large amount of fat in the abdominal area is a direct prerequisite for the development of heart disease, and therefore there is reason to think about it.
Separate food
Product Compatibility
Nowadays, quite a lot of articles and books are published that do not recommend consuming carbohydrates and proteins in the same meal. In particular, the so-called separate power supply system is built on this. It was developed at the beginning of the last century by the American doctor Hay. This system is based on the division of all products into “acidic” and “alkaline”, high-protein and rich in carbohydrates. “Neutral” food is included in a special group, i.e. fats, dairy products, cheeses, nuts, berries.
Hay advises eating alkaline foods (vegetables and fruits) for breakfast, protein for lunch, and carbohydrates for dinner. Products from the “neutral” group are allowed to be combined with others. The interval between main meals is at least 4 hours, but in between it is allowed to consume vegetables or fruits. In general, in a separate food system, the consumption of proteins (and especially meat) is limited.
According to statements by supporters of this system, it helps normalize metabolism, increase or decrease body weight, and also helps fight diseases. Hay himself was allegedly cured of glomerulonephritis with her help. However, for athletes, separate nutrition is unlikely to be beneficial. By following such advice, you can significantly slow down the growth of sports results.
A developing organism first of all needs a sufficient amount of various proteins. Carbohydrates contribute to the “storage” of protein - it is used to build muscle tissue, and not as a source of energy. Protein slows down the absorption of carbohydrates, thereby reducing their glycemic index. As a result, blood sugar levels remain more stable. A similar interaction is observed between fat and protein.
Natural source of energy
Glucose is a universal source of energy for all cells of the body. Energy is needed to build your own molecules, contract muscles, and generate heat. The sequence of glucose conversion reactions leading to the release of energy is called glycolysis. Glycolysis reactions can occur in the presence of oxygen, then we speak of aerobic glycolysis, or in oxygen-free conditions, then the process is anaerobic.
During the anaerobic process, one molecule of glucose is converted into two molecules of lactic acid (lactate) and energy is released. Anaerobic glycolysis produces little energy: one molecule of glucose produces two molecules of ATP, a substance whose chemical bonds accumulate energy. This method of obtaining energy is used for short-term work of skeletal muscles - from 5 seconds to 15 minutes, that is, while the mechanisms for supplying muscles with oxygen do not have time to turn on.
During aerobic glycolysis reactions, one molecule of glucose is converted into two molecules of pyruvic acid (pyruvate). The process, taking into account the energy spent on its own reactions, produces 8 ATP molecules. Pyruvate enters into further oxidation reactions - oxidative decarboxylation and the citrate cycle (Krebs cycle, tricarboxylic acid cycle). As a result of these transformations, 30 ATP molecules are released per glucose molecule.
Classification
Depending on their structure, there are several groups of carbohydrates.
Monosaccharides are small molecules that are not broken down in the digestive tract. These are glucose, fructose, galactose.
Disaccharides are small carbohydrate molecules that are broken down into two monosaccharides in the digestive tract. For example, lactose is divided into glucose and galactose, sucrose is divided into glucose and fructose.
Polysaccharides are large molecules consisting of hundreds of thousands of monosaccharide residues (mainly glucose) linked together. This is starch, meat glycogen.
Product table
Compounds with a glycemic index below 70 are usually classified as slow carbohydrates.
However, some substances that have high levels fall into this group because they:
- are associated with dietary fiber or other elements that impede the production of glucose;
- require additional elements for splitting, which also slows down the conversion process;
- contain fructose instead of glucose, which does not require the production of insulin.
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