Gut bacteria: key to health?

Dr. Andrea Bannert has been with since 2013. The doctor of biology and medicine editor initially carried out research in microbiology and is the team's expert on the tiny things: bacteria, viruses, molecules and genes. She also works as a freelancer for Bayerischer Rundfunk and various science magazines and writes fantasy novels and children's stories.

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Intestinal bacteria not only play a role in digestion. They affect the health of the entire body, including the brain, and even affect emotions. Are the little roommates a screw that can be turned to be healthier?

The human body is actually something like a flat share. Because in addition to your own cells, a lot of microorganisms live there. They are even in the majority: 40 trillion versus 30 trillion body cells, according to the latest estimates. Most of it is in the intestines.

For a long time it was thought that the intestinal roommates were passive and mostly harmless. Today scientists are beginning to reveal, bit by bit, how great the influence of the so-called intestinal microbiome - i.e. the entirety of the microorganisms living in the intestine - really is on human health. The extent is far from clear. One thing is already becoming apparent, however: the intestinal bacteria seem to have a much stronger influence on health than previously assumed.

"Who ate from my plate?"

In order for them to survive, they need enough food. And the bacteria take care of this more actively than you might think: They influence the human feeling of satiety. Usually, stretch receptors in the stomach and peptide messengers signal that one feels full after a decent meal. Conversely, such substances also indicate hunger, for example when lunch is still to come.

Some of the bacterial roommates build such peptide messengers. These then pretend, for example, that you are far from full - even if that is already the case. But not all intestinal bacteria want us to eat as much as possible.

The intestinal bacterium Escherichia coli about gets by with less sugar and food than other intestinal dwellers. When you eat, it produces satiety hormones after 20 minutes. In addition, it suppresses the desire for sweets through its sugar cell wall. It probably prevents excesses that would benefit hungrier competitors.

Controlled desire for sweets

To control human eating behavior, intestinal bacteria even influence how you feel. The lactic acid bacterium Bacillus infantis produces tryptophan, a precursor to the happiness hormone serotonin. If the mirror goes back, you feel depressed and reach for chocolate, ice cream, candies and the like more quickly.

Shouting provides supplies

Another example of a strategy for bacteria: Scientists have found that crying children have different intestinal co-inhabitants than non-crying infants. The hypothesis: These bacteria could affect the baby's mood in such a way that it cries all the time. Because what works for birds also works for humans: if the baby keeps drawing attention to itself, it will be fed more. And that also provides food replenishment for the intestinal bacteria.

Power to the brain

An experiment with mice has shown that the bacterial inhabitants of the intestine may even influence how anxious someone is. Rodents raised germ-free were given either intestinal bacteria from fearful animals or courageous animals.

The amazing thing: They then also displayed fearful or courageous behaviors. It even worked to "reprogram" the animals. Previously fearful mice became researched with the microbiome of courageous rodents themselves and vice versa. It is difficult to say whether the results of this study can be transferred to humans.

But the power of roommates probably reaches into the brain in another area as well: The latest research suggests that intestinal bacteria are associated with various mental illnesses, such as chronic fatigue syndrome. Significantly fewer different bacteria live in the intestines of patients than in healthy people.

Apparently, bacteria in the intestine can also directly influence the nerve cells in the brain. A 2015 study by the Freiburg University Medical Center showed that germ-free mice only developed a stunted clean-up team in the brain. Probably because of the lack of short-chain fatty acids, which gut bacteria produce when food is broken down and which travel to the brain with the blood. These activate the important brain garbage disposal. If it doesn't work properly, neurodegenerative diseases can develop.

Booster for the immune system

It has long been known that a high-fiber diet lowers the risk of asthma. Apparently, intestinal bacteria are responsible for this effect. They break down the fiber and produce fatty acids that are carried with the blood into the bone marrow. There they influence the production of certain immune cells. These migrate to the lungs, where they slow down the excessive immune response typical of asthma.

The intestinal bacteria not only play a role in allergies and autoimmune diseases, they also strengthen the immune defense against infections and fight influenza viruses and co. Experiments with mice show: If the intestinal microflora is missing or if it is severely decimated, the infection is much more serious.

WG casting?

With so much influence on health, the question naturally arises: Can you choose your intestinal roommates? And who would you actually like to let live in your intestinal flat share?

Basically, the more colorful the shared apartment, the better. Scientific studies show a correlation between the variety of microorganisms in the intestine and health. If there is a serious illness, such as chronic intestinal inflammation, on the other hand, there are far fewer different bacteria living in the intestine than in healthy people.

Tea and yogurt

In fact, you can influence your roommates through your diet. The following applies: Food rich in fat and sugar limit the variety of organisms living in the intestine, fiber increases it.

A study by the Catholic University of Leuven in Belgium also indicates that specific foods also increase the diversity of the microbiome: These include yogurt, buttermilk, coffee, tea or red wine. Researcher around Dr. Jeroen Raes examined stool samples from more than 6,000 people and asked them about their eating habits.

So-called probiotics, which are microorganisms with particularly health-promoting properties for humans, are also considered to be beneficial for intestinal bacteria. These can be found in various foods, such as probiotic yogurt.

Disruptive medication

On the other hand, drugs have a strongly negative influence on the small roommates of the intestine. This is obvious for antibiotics, which often kill not only the pathogen but also various other bacteria. Laxatives, antihistamines, heartburn drugs, statins, the pill or hormones also affect the bacteria in the intestine.

Open questions

Despite intensive research, more questions are unanswered than answered, according to Raes. So it is obvious that you do not want to have any disease-causing roommates. However, which microorganisms are particularly beneficial for whom and which, for example, could help suppress certain allergies, must first be researched in detail.

It will probably be some time before the small intestinal roommates can be influenced specifically for medical therapies. As a next step, Raes and his colleagues want to examine stool samples from 40,000 test subjects in order to find out more about the influence of the intestinal flat on human health.

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