‘Hou je brein gezond, met goede bacteriën’


The road to a healthy brain largely runs through your intestines. Take good care of the billions of bacteria that live there and you reduce the risk of depression, obesity or Alzheimer’s, says psychiatrist Iris Sommer.

Lidwien Dobber

High above physical concerns, safely in its skull cocoon lies our brain. Sterile, unapproachable, the master of the body. That was the idea when Iris Sommer studied to become a doctor and later a psychiatrist in the 1990s. At the end of the twentieth century, the first cracks appeared in that image and now it is in tatters.

The billions of bacteria, fungi and archaea (‘primeval bacteria’) in our intestines are at least partly responsible for many conditions that have long been regarded as purely psychological or genetic – anxiety, depression, Alzheimer’s, Parkinson’s, autism, ADHD, obesity –. They send messages to the brain. So it matters which bacteria populate your intestines, because each strain has its own function. Rule of thumb: the more varied your intestinal flora, the better the information exchange with the brain.

Iris Sommer (Roermond, 1970) studied medicine at the VU in Amsterdam and obtained her PhD at Utrecht University for research into schizophrenia and voice hearing. She is professor of psychiatry at the University Medical Center Groningen. She previously wrote, among other things Faltering brains, The woman’s brain and the cookbook Feed your brain.

It didn’t take long for commerce to exploit this insight. There is a huge range of drinks, yogurts and pills with probiotics, and the message is: eat, drink, sweets or tut (there are also cosmetics with probiotics) to keep yourself healthy! Sommer: “People who don’t feel well sometimes spend a fortune on it. I wish them to spend their money better. It has rarely been proven that these supplements work. You can say: if it doesn’t help, it won’t hurt, but we don’t know that either.”

It is exciting and promising, says Sommer. Her book was published this week The bacteria and the brain, in which she writes what we do know. “Our knowledge increases every month. My book had not yet gone to the printer and I already saw new studies and thought: oh, they should be included! In five years I can already write part 2. It makes me very happy, those bacteria are such incredibly interesting guests.”

Can you give an example of promising research?

“The intestinal flora is formed from the moment a child is born. A baby passing through the birth canal ingests vaginal fluid. That may sound gross, but that fluid contains many bifidobacteria, which are necessary to digest breast milk. Exactly what the child needs. The breast milk nourishes the baby and the bacteria in its intestine. This is how the intestinal flora is formed.

“About 18 percent of children in the Netherlands are born by caesarean section. Their first bacteria do not come from vaginal fluid, but often from the skin of their moved parents when they hold them in their arms. That is a relatively large number of staphylococci and streptococci, which are of little use to digest milk. Bifidobacteria also settle in the intestines of these babies, but the difference in intestinal flora remains visible for a long time. And there are indications that intestinal inflammation, allergies, asthma, eczema and obesity can be the late consequences of this.”

These are physical consequences, but it also seems to make quite a difference for the development of the brain how a baby’s intestinal flora is composed, you write. How does that work?

“The brain is far from finished at birth. We know from mouse research that almost the entire brain contains receptors for a small bacterial substance, peptidoglycan, that controls brain development.

“Because the intestinal bacteria themselves do not reach the brain. If your intestine is healthy, it keeps the bacteria inside. And otherwise there is a second obstacle: the blood-brain barrier, which protects the brain against invaders.

null Image Patrick Post

Image Patrick Post

“But intestinal bacteria have a cell wall. As they divide and grow, they shake them off. It’s a bit like a moulting dog: in my house you now find dog hair in every corner of the room. This is how I imagine the intestine: if it is well colonized, there is a layer of that bacterial substance on the ground. This substance is much smaller than the bacteria itself and does end up in the blood and brain.

“Now you can have mice grow up sterile, without intestinal bacteria and therefore without that bacterial substance. These mice exhibit abnormal behavior that vaguely resembles ADHD or perhaps autistic disorders. And if you examine the brain, you see abnormalities there.

“Mice are not people, I want to emphasize that. But what we see in people with ADHD and autism is that they were more often born via caesarean section, were breastfed less often and were given antibiotics more often as a very young child. These are all three factors that cause the intestinal flora to develop less quickly and less diversely. We do not know the causal relationship, it could also work the other way. And if there is no connection, we will find out.”

And if there is a connection?

“Then we can see if we can do something about it. There are a handful of studies in which women use probiotics in the first weeks before giving birth and a few months afterwards. For example, you can make a selection of mothers who already have a child with autism or ADHD. Look, autism is largely genetic, so what you can do with the environment is certainly not everything. But there are also identical twins where one has it and the other does not. That gives hope.”

There also seems to be a connection between stress and your intestines, which goes beyond the fact that stress gives you a stomach ache.

“This is also mouse research. A small mouse is visited by a larger, aggressive mouse in its cage. That little one feels attacked. If you repeat that a number of times, such a mouse will experience something in English again and again social defeat is called. He will lose out. There are mice that suffer from this much more than others. They no longer want to meet other mice, they don’t even want to eat sweets anymore; They leave sugar water, which mice love, alone.

“It is broken behavior that you also see in people. Suppose there are ten researchers and we each write ten proposals for a grant. And we all get ten rejections. You can have one rejection, but ten is really a lot. Then you start to doubt yourself, and four out of ten maybe so much that they enjoy fun things less, stop going to parties or even think: I’m quitting this job.

“It would be fantastic if you found out what that difference is. Because stress and disappointment are part of life. You may be impressed by that, but it’s nice if you don’t break your head.

“The unconstrained mice turned out to have a certain strain of lactobacilli in their intestines. We know this type of bacteria very well, we use it to make cheese and yoghurt. If the damaged mice were given that strain, they became less vulnerable.”

How does that work?

“When the big mouse visits, the brain experiences social stress and sends a signal to the immune system. Many immune cells are on the outside of the intestinal wall, on the body side, that is their school, there they learn what can do harm and what they should attack. One specific type of immune cell responds to stress. It multiplies, enters the blood and also travels to the brain, where it settles in the meningeal membrane. From there it sends a substance to the brain that causes that broken behavior.”

Can you also investigate something like this in humans?

“I would like to conduct research together with occupational health and safety doctors, who see people when they are in a labor conflict and are vulnerable to burnout. What is it like if you give them that strain of bacteria? Maybe then they’ll snap less, that would be great. In combination with psychotherapy, yes, as a psychiatrist I like to bring those two completely different angles together.”

Speaking of which, you see that there is resistance to the idea that substances play such a major role. “Our pride gets in our way,” you write. What do you mean?

“Animal behavior can easily be traced back to messenger substances in the brain, including that of monkeys, even chimpanzees, 99 percent the same as us. But as soon as you touch humans, as soon as you say that you can understand something about human behavior through this research, it creates resentment: I am more than my brain, I have my own will. But one does not exclude the other.”

While anyone who embraces this idea can do a lot to become healthier or stay healthy for longer. Cook yourself, chew well, brush your teeth, don’t drink alcohol, write.

Laughing: “Yes, I become a bit directive. But remember: you eat for yourself and for your bacteria. They need fiber, so whole grain things, vegetables, fruit. And as few ready-made meals as possible, with preservatives that ensure that bacteria do not grow on your pizza. Because that’s what they also do in your intestines: ensure that bacteria do not grow.

“Emulsifiers, which ensure that there are no lumps in the béchamel sauce of your ready-made lasagna, are disastrous for your intestinal flora. Alcohol is what we use in the hospital to disinfect, to kill bacteria. Alcohol also does that in your intestine. All in all, we are creating a hostile environment there.”

And the elderly are at risk because they often eat less well, take antacids so that the stomach stops fewer ‘bad guys’ and with an immune system that is also a day older.

“Yes, and their intestinal flora also becomes one-sided. Many elderly people have completely lost the bifidobacterium, while research shows that bright centenarians often still have it on board. Humans have been living with bifido and the lactobacillus that we talked about earlier for a long time, because we use them for our food.

null Image Patrick Post

Image Patrick Post

“The refrigerator is not that old, we used to ferment our food or put it in pickles to make it sustainable. Good bacteria benefit from a more acidic intestines. So back to the sauerkraut, the yogurt and the buttermilk! And I also see that trend, although I may be in a bubble: people are fermenting their food again and the kefir is not available.

“All those kinds of things help with healthy aging. It’s crazy how old we get and that’s fun, if your brain continues to participate. Anyone who is careful with their brains at least stops smoking, moderates their alcohol and cooks their own meals.”

And maybe don’t eat too much? Being overweight is also a risk.

“The bacteria research also sheds new light on this. Look, anyone who eats a lot of calories and fat becomes fat. It’s that simple. For a long time I thought that being overweight was simply a deduction: that’s how many calories you consume and that’s how many calories you burn. But whether you become fat also has to do with your intestinal bacteria, because some people really eat every last calorie from a meal. So there are people who don’t eat much, who try so hard to get slim and still don’t lose weight.

“One last mouse study. If you feed fat mice healthy food, they usually become thinner. But not all. Now mice have a habit of chewing each other’s droppings. So the fat mice were placed with thin mice, where they chewed droppings and thus ingested other people’s intestinal flora. Then they too became thin.

“We cannot avoid eating less and healthier, but we may be able to help people who have difficulty losing weight by improving their intestinal flora. Although we don’t know exactly how yet.”

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Iris Sommer
The bacteria and the brain
Atlas Contact; 224 pages. €22.99

Also read:

Bacteria in the intestines influence depression, according to thirty years of research

Intestinal flora plays a role in depressive complaints, a large Dutch study shows. The finding paves the way for new forms of treatment.


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