Digestive stations part 1 — from mouth to intestine, this is what happens in your stomach
Unconsciously, we do it all the time — and yet very few people know about their digestion. Even though we often rely on our “gut feeling”, believe that the way to a man’s heart is through his stomach, and that anger or stress spoils our appetite, we don’t really know how our digestion actually works. Yet this knowledge forms the basis for understanding many diets, nutrition methods and the path to a healthier life. What happens in our gut, which foods have a lasting impact on our digestion and health, and how human behavior can affect our digestion is the topic of today’s article.
Our facts-to-go briefly & concisely summarized for you!
- Digestion, or rather the preparations for the digestive process, already begin when we only think about eating
- The vagus is the longest of our twelve cranial nerves and runs from the brain through the neck, extends across the chest cavity, splits into left and right vagus and leads to the heart, lungs, stomach, pancreas, intestines, etc. So the vagus is directly connected to everything that is important. It controls blood sugar, breathing, heart rate, secretion of digestive juices, lacrimal fluid, etc.
- Even an eight-week consumption of two apples a day can slightly lower cholesterol levels, as well as improve blood vessel function. It is interesting to note that this effect occurs only when whole apples are consumed, and not apple juice alone.
- The polyphenols and pectins abundant in apples are unfortunately lost during processing into juice products and end up in the trash
- Bloating from plant-based and high-fiber foods is normal and usually not a sign of intolerance! Cellulose — a carbohydrate that can hardly be utilized by digestive juices — is “fermented” by intestinal bacteria. This fermentation produces gases, so it is understandable that with predominantly plant-based foods, correspondingly more gases are formed in the large intestine.
Digestion station №1: the mouth
Have you ever thought about the purpose of having “water in the mouth” before eating? Our digestion would only work half as well if we didn’t subconsciously prepare ourselves for it. Digestion, or rather the preparations for the digestive process, begin even when we are only thinking about eating. The connecting pathway between the head and the digestive tract is the so-called vagus nerve, which reflexively controls all digestive organs as well as saliva production and transports all information from the intestines to the brain and back again. The vagus is the longest of our twelve cranial nerves and runs from the brain through the neck, extends across the chest, splits into the left and right vagus, and leads to the heart, lungs, stomach, pancreas, intestines, and so on. So the vagus is directly connected to everything that is important. It controls blood sugar, breathing, heart rate, secretion of digestive juices, lacrimal fluid, and much more.
Apart from the largely unconscious digestive steps, the mouth is the first digestive station responsible for the conscious recognition, mechanical grinding, disinfection and moistening of food. As mentioned in our previous article on digestive enzymes, saliva already contains various enzymes that can break down carbohydrates into simple sugars. If you keep (unsweetened) porridge or bread in your mouth long enough, you will notice how much sweeter it tastes after a while. In addition, tongue base lipase, which is also found in saliva, prepares dietary fats (triglycerides) for digestion in the stomach. Last but not least, saliva also contains disinfecting substances such as fluorides or rhodanide ions.
Digestion station №2: the stomach
After the conscious act of swallowing, unconscious and undulating muscle movements of the esophagus ensure that the food is transported into the stomach. When the mush reaches the bottom, the “gate” to the stomach opens. This is a ring-shaped smooth muscle located between the esophagus and the stomach. After the food has completely reached the stomach, this musculature closes the stomach entrance again so that nothing can spill back into the esophagus as the acidic stomach contents mix. When there is a lot of stress and low vagus nerve activity, the stomach movements slow down and the sphincter muscle becomes slacker, which can lead to increased bloating, heartburn, food remaining in the stomach longer, and belching.
The fact that plant foods have a positive influence on our digestion, our cardiovascular system and our life expectancy is now nothing new. Exemplary scientific evidence in this regard is provided by a study from Great Britain, which clinically investigated and characterized the effect of apples. Already an eight-week consumption of two apples daily could slightly lower the cholesterol level, as well as improve the blood vessel function. Interestingly, this effect occurred only when whole apples were consumed, and not apple juice alone. The polyphenols and pectin abundant in apples are lost during processing into juice products and end up in the trash. But together with dietary fiber, these very substances seem to be necessary for the cholesterol-lowering effect of apples in healthy people. So clear apple juice is not an advisable substitute for whole, fresh apples.
Digestive station №3 — the intestine.
The duodenum — the next digestive station — contains enzymes that break down protein, carbohydrates and fat for all 3 major nutrients. These come from the digestive juices released by the pancreas into the duodenum. Thus, the pancreas alone contains 3 different enzymes for breaking down carbohydrates to the water-soluble monosaccharides, plus the enzyme trypsin, which breaks down proteins into water-soluble amino acids, and finally the enzyme steapsin, which breaks down the fat present in food into glycerol and fatty acids. Glycerol is water-soluble and can therefore pass through the intestinal wall, but fatty acids cannot do so easily. They have to be helped by bile acid, which is contained in the bile produced by the liver and enters the duodenum with it.
By combining the fatty acid with the bile acid, the fatty acids are enabled to pass through the intestinal wall. Immediately after this passage, this coupling is broken again, the fatty acids recombine with the glycerol, and in the fine lymphatic vessels of the intestinal wall, small fat droplets are already found again, which are now supplied to the organs as nutrition.
In the small intestine, which follows the duodenum, certain glands also secrete a digestive juice that once again contains enzymes that break down the proteins, which have not yet been completely broken down, into amino acids and the carbohydrates into tiny, simple sugars.
Finally, in the large intestine, the bacteria present there break down those food components that have not yet been sufficiently attacked by the digestive enzymes. The cellulose — a carbohydrate that can hardly be utilized by the digestive juices — is “fermented” by the intestinal bacteria. This fermentation produces gases, so it is understandable that a predominantly plant-based diet also produces a correspondingly greater amount of gases in the large intestine. Another type of bacteria in the colon breaks down the remaining proteins by putrefaction. This process produces products that not only smell bad, but can also have a toxic effect if they are not removed from the intestine in time, for example as a result of constipation. In the large intestine, so much water is finally extracted from the previously thin food pulp that the remainder, consisting of indigestible food components and an abundant amount of bacteria, acquires the usual consistency of the stool — digestion is complete!
Text sources:
(1) Herold, Gerd: Innere Medizin 2020. Kapitel “Gastrointestinale Gasbeschwerden” (Eigenverlag, 2019)
(2) Leung, Po Sing: The Gastrointestinal System. Gastrointestinal, Nutritional and Hepatobiliary Physiology. Kapitel 6 “Digestion and Absorption of Carbohydrates and Proteins” (Springer Verlag, 2014)
(4) Blähungen — Meteorismus. Ratgeber für Patienten. (Gastro-Liga) (PDF)
(5) Was gegen Blähungen hilft (Berufsverband Deutscher Internisten)
(6) Koutsos A, Riccadonna S, Ulaszewska MM, et al. Two apples a day lower serum cholesterol and improve cardiometabolic biomarkers in mildly hypercholesterolemic adults: a randomized, controlled, crossover trial. Am J Clin Nutr. 2020;111(2):307–318. doi:10.1093/ajcn/nqz282
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