Intestinal flora is a collective name for bacteria and other microorganisms that are naturally found in the intestine. The bacterial flora is thought to consist of between 300–1000 different species, but the majority, about 99%, consists of about 30–40 species. 1 The composition of your gut depends on a number of factors. For example, how you were born plays a major role, i.e. whether you were born vaginally or by caesarean section, how you eat, the pH value of your gut, whether you have taken courses of antibiotics, etc.
It is often said that some of the flora is more permanent and some is temporary and dynamic. This means that some of the intestinal flora, which is formed early in life, remains as it is while some can be influenced by, for example, a healthy lifestyle. Our intestinal bacteria are so numerous that you could say that we are actually more bacteria than humans, as we have more bacteria than human cells in our bodies! It is therefore not surprising that they play a very large role in our well-being and that they affect us in many different ways, both good and bad.
Improves nutrient absorption
The primary absorption of nutrients takes place in the stomach and small intestine, but some is also absorbed in the large intestine thanks to our intestinal bacteria. Approximately 85% of carbohydrates, 65–95% of protein and all fat are absorbed before reaching the large intestine. Indigestible carbohydrates and proteins continue to the large intestine and account for between 10%–30% of total energy intake! Without the bacteria, these carbohydrates and proteins would instead leave the body via the stool without further absorption due to the limited digestive capacity of the large intestine. 2 During breakdown, or fermentation, in the large intestine, the short-chain fatty acids acetic acid, butyric acid and propionic acid are formed, among others. These are important for maintaining intestinal homeostasis (balance). They also serve as fuel for the intestinal epithelial cells and strengthen the intestinal barrier. In addition, the short-chain fatty acids are involved in the communication between the intestine and the brain, the so-called “gut-brain axis”.
Vitamin production
Several types of bacteria that are very common in our intestines also have the ability to produce vitamins for us! The bacteria can produce almost all B vitamins, evenB12 . They also produce vitamin K2 . It has not been fully mapped out how effectively these vitamins are absorbed by the body as they cannot be absorbed via the small intestine, which is otherwise the place where vitamins are absorbed. The small intestine is located before the large intestine. However, it has been seen that the vitamins produced by the intestinal bacteria can actually be absorbed in the large intestine via other mechanisms and that they are also used by the bacteria themselves. 3
The connection to the immune system
You have probably heard the phrase “the immune system is in the gut”, and it is actually true. Between 70–80% of the immune system cells are in the gut. It is also the case that the intestinal mucosa protects us against pathogens that otherwise risk spreading further into the body. It is therefore important to have a healthy intestine so that the mucosa keeps tight and does not start to leak through disease-causing bacteria and viruses. The bacteria in the intestine are sometimes also called “the immune system’s personal trainer” as they help the body’s immune cells distinguish which microorganisms are dangerous and which are harmless to us.
We have many different types of bacteria in our intestines, some good and some not. The composition of the bacteria depends on how we live, i.e. what we eat, how much stress we have, but some of the intestinal flora is already formed at birth. There are several ways to influence your intestinal flora, which in turn affects your immune system. Adding good bacteria in the form of various lactic acid-forming bacteria is an easy way, these are also called probiotics. They are found in, for example, dietary supplements, certain types of yogurt, fermented vegetables, and other fermented foods.
Lactic acid bacteria
There are many different groups of good intestinal bacteria, one well-known group is lactic acid bacteria . Lactic acid bacteria got their name because they produce lactic acid when they ferment. They live by breaking down sugars into lactic acid and act as a protection against other bacteria. They also help to increase the amount of other good bacteria in the intestine. The fact that they are called “lactic acid bacteria” does not mean that they contain milk or that people who are intolerant to milk or lactose cannot eat them. There is therefore no connection to cow's milk, but only to the substance lactic acid. Two of the most common lactic acid bacteria families are lactobacilli and bifidobacteria.
The balance between good and bad bacteria
The large intestine contains up to 1.5 kg of bacteria in a delicious mix of species. Some are good and health-promoting, and some are less good and downright harmful to health. To feel good, we need a balance between these. You can achieve this by eating a varied, healthy and high-fiber diet, reducing stress in your everyday life and exercising regularly. A good complement to these habits is to add good bacteria via dietary supplements. Processed food, sugar and alcohol are examples of foods that feed the less good bacteria and negatively affect the intestinal flora, which can create an imbalance.
Where are good bacteria found in the diet?
Examples of foods rich in lactic acid bacteria include fermented vegetables such as sauerkraut and kimchi, some types of fermented milk, some types of yogurt, kombucha (fermented tea), sourdough bread, miso soup and tempeh (fermented soybean product). If you want to add a larger dose of good bacteria, a high-quality dietary supplement is an easy option. Today, there are many well-documented strains to choose from and often a mixture of bacterial strains is present in dietary supplements to get a wide variety.
Prebiotics
It is also very important to feed your good gut bacteria with fiber that makes them thrive and feel good. These fibers are called prebiotics or prebiotic fibers and are found in fruits, berries, vegetables, legumes and whole grains, among other things. Boiled, cold potatoes are also great as they are rich in resistant starch that the bacteria like.
Serotonin and dopamine are produced in the gut.
Gut bacteria affect many parts of the body, including our brain. When the bacteria eat the prebiotic fibers I mentioned above, neurotransmitters such as serotonin and dopamine are formed. Serotonin is a substance that regulates worry, anxiety, sleep, alertness, pain sensations, intestinal motility and even feelings of satiety and hunger. You may know that serotonin is found in the brain, but did you know that between 80–90% of all the body's serotonin is produced in the gut? Dopamine is a neurotransmitter strongly linked to the brain's reward system and is the substance that gives us the feeling of getting a "kick". About 50% of the body's dopamine is formed in the gut. There is still much to discover regarding the importance of the gut for health, but researchers seem to agree that it plays a major role.
Sources:
- https://web.archive.org/web/20140512214805/http://www.godamagbakterier.se/probiotika?gclid=CJvs1J6Umr4CFULecgodTQQAiA
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3601187/
- https://www.frontiersin.org/articles/10.3389/fnut.2019.00048/full
