Many nutrients from food are useful only if properly digested by the body. From eating to absorption, food makes a long, tangled and difficult journey. The digestive process of a person that goes through the digestive tract – from the mouth to the anus, acts as a complex inventory management system. During this process, food is split into constituent molecular parts to deliver them to their final destination: trillions of cells in your body, where they combine into tiny mechanisms and energy sources that provide your vital activity.Digestion is an amazingly effective process, but disturbances (some of them genetic, others arose from decades of malnutrition) underlie the painful sensations and progression of chronic diseases. One study showed that 70 percent of adult Americans experience unpleasant gastrointestinal symptoms due to impaired digestion, absorption, or unhealthy bacterial background in the digestive tract, apart from certain diseases of the digestive system.1 Properly assessing and adjusting your digestive process is very important for well-being and preservation of health.We almost can not consciously control our digestive process. Through the mouth and nose, taste and olfactory receptors, we get pleasure and important information coming to the brain about what we eat. But after we have swallowed the food, only weak nerve receptors are reported to the brain. For the most part, the process is “on autopilot” and is controlled by reflexes through local nerves and sensitive metabolic pathways. We can influence the digestive process through nutritional supplements and, if necessary, through medications. But a healthy diet is the most important thing for maintaining and restoring the shaky balance of the digestive process. HOW DOES DIGESTION WORK?The gastrointestinal tract of a person is depicted on page 87, the figure shows all the organs involved in the process of digestion, which takes place in several stages: Stage 1 . Digestion begins in the mouth, when in the process of chewing food is divided into small particles, convenient for processing. Salivary glands produce a day about a liter of saliva, by which the dry food is moistened and dissolved (the acid-base balance changes) to maintain the optimal (alkaline) pH level. Amylase is the main digestive enzyme of saliva, which begins to break down starches (polysaccharides) into glucose (monosaccharide) and maltose (disaccharide). Disinfection of the oral cavity with saliva is also of great importance for oral hygiene.Meticulous chewing is necessary for health. If you ingest solid food before it has been chewed and mixed with saliva, you make it difficult to digest, which can cause it to break and lead to an upset in the intestines. Due to insufficiently thorough chewing, the digestive tract is forced to secrete more potent digestive enzymes, which can immediately lead to increased gas production and swelling. Over time, these enzymes can damage the stomach and digestive system. So eat slowly. Step 2.Then the food passes through the esophagus, which by reflexive peristaltic contractions (vermicular movements) directs it to the stomach. The stomach can expand to accommodate different volumes of food. It serves as a temporary intermediate station, from which food gradually enters the intestine with the help of peristaltic contractions and contractions of the walls of the stomach. Step 3.Cells of the mucous membrane of the stomach lining its walls, secrete about a liter of gastric juice daily. Juice is an acidic natural body fluid, which mainly consists of hydrochloric acid with a pH between 1.0 and 2.0. This acid dissolves the food to a practically liquid formation called “chyme”. Gastric juice also contains digestive enzymes, in particular pepsins, which begin to break down proteins into their constituent amino acids. When the chyme leaves the stomach, these digestive processes break down about 30-50 percent of carbohydrates and 10-15 percent of proteins, while fats at this stage are almost not split.In gastric juice contains a special protein called the internal factor of the Castle, necessary for absorption of vitamin B12. Violation of absorption of vitamin B12 interferes with the normal metabolic cycle of folic acid, which increases the level of homocysteine ??(see Chapter 13). To identify this disorder, it is not enough just to make an analysis of the vitamin B12 content in the blood, because it does not indicate whether the body is able to use this nutrient. It is better to check the blood level of methylmalonic acid, an intermediate metabolite, for the cleavage of which vitamin Bl2 is required. If the level of methylmalonic acid in the blood is increased, it means that vitamin Bl2 does not fulfill its function, regardless of its level in the blood.