‘Tell me what you eat and I’ll tell you if you’re happy’: Animal studies show that the gut ‘communicates’ with the brain through microbes that can cause anxiety and stress. And how does the microflora affect the emotional state of people? And can food cheer you up?
The debate about whether we can influence our state of mind by choosing certain products does not stop until now. Chocolate and noodles are considered “happy”, but, logically, fish with its omega-3 fatty acids should rather protect against a depressive state. And yet, until there is no concrete evidence, we continue to consume chocolate in huge quantities in order to feel the tides of joy.
How can one confirm the fact that the state of the intestinal flora still affects not only human health, but also the state of his soul? At least the fact that many patients with problems of the gastrointestinal tract suffer from mental disorders. Irritable bowel syndrome occurs in approximately 50% of depressed and anxious patients; bowel problems are often characteristic of autistic people.
So do probiotic yogurts help with depression? Can sauerkraut crowd out anxiety disorders, and a well-chosen diet alleviate autism symptoms?
Bridge between gut and brain
It has long been known that bacterial infections can affect mood. This influence occurs through the immune system: certain inflammatory markers, such as cytokines (a group of molecules that provide signaling and are involved in the functioning of the immune system), are activated, resulting in increased symptoms of depression, anxiety and chronic fatigue. However, some researchers, including physician Mark Lith of the University of Texas, believe the microbes may be affecting the brain in a different way. He injected mice with a small amount of a diarrhea pathogen, to which the body reacted without any signs of infection. Lit connects the transmission of information with the vagus nerve.
The limbic system, which is responsible for processing emotions, is actively involved in these processes.
The vagus nerve connects the brain to the intestine through the spine using efferent (centrifugal) connections that direct signals from the brain to the digestive tract, while afferent (centripetal) nerve bundles transmit information from the intestine “up”. The limbic system, which is responsible for processing emotions, is actively involved in these processes.
In a recent experiment, researcher Melanie Klarer of the ETH Zurich severed afferent connections in mice. Then a situation was created that causes anxiety and stress in animals: a brightly lit cage, no shelter. As a result, the experimental mice became more fearless. “It seems that signals from the stomach to the brain influence the manifestation of innate fear,” explains Urs Meyer, co-author of the study.
courage bacterium
Immunologist Sven Petterson of the Karolinska Institute in Stockholm has been studying the effects of bacteria on brain biochemistry for several years in a mouse study. For this sterile mice (without germs) were compared with normal mice. In general, sterile animals were more active and courageous. It turned out that this quality can be changed – however, only in young individuals, but not in adults, if they are “populated” with bacteria. “It is possible that there is a time window in which bacterial colonization has a lasting effect on the brain,” the scientist says. In parallel, Petterson studied the genes that play a role in the manifestation of anxiety: they were suppressed in sterile mice.
Pathogenic microbes and some drugs increase intestinal permeability
However, there may be another way that does not affect the neural pathways. Certain substances can enter the blood and brain through the intestinal barrier, which alters the human condition. It turns out that sports, pathogenic microbes, and certain drugs, such as ibuprofen, increase intestinal permeability. This allows more “bad bacteria” to disturb the immune system and affect the brain.
However, it has not yet been proven that an unhealthy diet or the gluten component of wheat makes the intestinal wall permeable. Proponents of “weak gut syndrome” believe that this systemic inflammation leads to numerous diseases such as food allergies, migraines, chronic fatigue syndrome, asthma, autoimmune diseases, skin diseases, and autism. There have even been case reports of gluten leading to hallucinations, schizophrenia, and psychosis. However, there is no scientific evidence yet that abstaining from gluten and certain food additives improves these conditions.
Do probiotics help?
Studies of the effect of probiotics on the intestinal flora have not yet led to any sensational or large-scale results, but experiments on mice, for example, have shown that lactobacilli affect emotional behavior through certain receptors.
Studies are periodically conducted on humans: scientists are trying to identify the effect of probiotic drinks on mood. In a 2013 study by UCLA neuroscientist Emeran Mayer, 12 healthy women consumed two probiotic milk drinks a day for four weeks, while 11 women drank only milk and 13 women acted as the control group. As a result, the “probiotic group” behaved more relaxed, and MRI data showed different foci of activity in their brains. In another study, the microbe Bifidobacterium infantis improved irritable bowel syndrome in those who suffered from it. There is also evidence that certain bacteria may help relieve depression and chronic fatigue syndrome.
While it is impossible to draw unambiguous conclusions about the usefulness and necessity of probiotics
However, these human studies have one drawback – too small a sample of participants. Some projects are funded by probiotic manufacturers, making them less independent and less objective. Therefore, it is not yet possible to draw unambiguous conclusions about the usefulness and necessity of probiotics and their impact on our emotional state. “However, there is a possibility that certain diets, such as the Mediterranean or traditional Japanese diet, reduce the risk of depression,” said Eva Selhub, a physician at Harvard Medical School. Both diets include a lot of fermented foods – wine, yogurt, green olives, tea, soy sauce – that provide the body with “good” bacteria.
At the same time, many scientists refrain from unequivocal conclusions. “We don’t have enough evidence to draw conclusions about people,” complains Dirk Haller, a microbiologist at the Technical University of Munich. There is definitely a connection between the microbiome and the brain, but it is not yet clear how they interact. More research is needed.”
Recently, the European Commission allocated 13 million euros to investigate how microbes get energy from food and affect brain function. Perhaps soon we will have convincing evidence of the connection between the “population” of our intestines and our mood.
Source: spektrum.de