Are we manipulating our intestinal flora?

The microbes in the gut could even affect our eating preferences

About the "belly brain", hormones, toxins and receptor changes our intestinal bacteria could manipulate us. © UC San Francisco
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Whispers from the stomach: It is well known that the bacteria in our intestines influence our health. But now US researchers suspect that the intestinal flora even manipulated our behavior: About signal substances and the "belly brain, they could even affect our food preferences. We then eat well what our microbes need right now. That sounds crazy, but some evidence speaks for it.


The bacteria in our digestive tract are clearly in the majority: we carry far more microbial cells than our own body cells in us. Their composition varies according to our health and diet. At the same time, however, the microbes also compete with each other and each have different nutrients: some thrive when we eat a lot of sugar, others with rather greasy food. "There are a lot of interests in our microbiome, some of them are in line with our own nutritional goals, others are not, " explains co-author Carlo Maley of the University of California at San Francisco.

And that's exactly where researchers come in: What if the intestinal flora is even actively providing us with the nutrients it needs? "The bacteria in the gut are manipulative, " says Maley. In their publication, the scientists are putting forward a whole series of evidence that the intestinal flora can also influence the behavior and moods of animals and humans and also explain how this happens.

Intestinal flora influences the mood

Thus, experiments show that mice with a bacteria-free intestine have altered taste receptors for sweet and greasy. In other experiments, researchers found that many inhabitants of our digestive tract, including the common gut germ Escherichia coli, produce the hormone dopamine. This plays an important role in the addictive behavior, but also in the sense of satisfaction that we feel when we indulge our cravings for sweets or junk food. display

The fact that the intestinal flora can influence moods and behavior, as also testify to some mouse experiments, as the researchers report: planted germ-free mice, the intestinal flora of particularly anxious animals, they were also more anxious, conversely, animals could also make courageous by microbial transplantation. One particular lactic acid bacterium attenuated the release of stress hormones in mice in another experiment.

Whisperings about the "belly brain"

And also in the "belly brain" the intestinal flora could manipulate our mood and appetite according to the scientists. The vagus nerve connects about 100 million nerve cells in the digestive system with the brain and is thus the central communication axis between the head and stomach. However, the nerve cells of the digestive tract carry receptors that respond to the presence of certain bacteria and their degradation products, as experiment show.

At the same time, the vagus nerve plays an important role in our eating behavior and body weight. "Results so far indicate that microbes can manipulate the signals of the vagus nerve and also our eating behavior, " say the researchers.

No one-way street

So are we helpless at the mercy of the wishes of our microbial roommates? Probably not, reassure the researchers. Because in addition to our ability to make conscious, rational decisions, we can also manipulate the intestinal flora on our part, as studies also show: "Our diet has a tremendous impact on the microbial populations in our intestines" says Maley.

Pre- or probiotic foods, changes in diet, antibiotics or even excretions of excrement can alter the composition of the intestinal flora. This could therefore be used deliberately, for example, to decimate those species in the intestine that promote, for example, overweight and desire for the unhealthy, the researchers said.

Whether our microbial roommates actually have such a power over us, must now be clarified in further experiments. However, the researchers consider it very likely that the intestinal flora affects more than just our digestion and the purely physical condition. "We are just beginning to understand the importance of the microbiome for human health, " said co-author Athena Aktipis of the University of California at San Francisco. (BioEssays, 2014; doi: 10.1002 / bies.201400071)

(University of California, San Francisco (UCSF), 19.08.2014 - NPO)