Want to keep your brain healthy? Take good care of your gut. Psychiatrist and VU alumna Iris Sommer emphasises the significant role gut bacteria play in combating diseases like depression and Parkinson's.

A psychiatrist researching the gut is unusual, isn't it?

„I understand that. I had to do quite a bit of extra studying. During my time at VU, the brain was seen as an isolated organ, unrelated to the rest of the body. Now, we realise that understanding the brain requires considering various other bodily processes, including the immune system, and now the gastrointestinal tract and microbiome."

„I work at the Academic Hospital in Groningen, where interdisciplinary collaboration among specialists is encouraged. I have access to an immunologist, a gastroenterologist, and a microbiologist for further training. We collaborate on research, allowing for a deeper exploration in psychiatry."

In your book 'The Bacteria and the Brain', you give an overview of research in this area by various scientists. You write that the billions of bacteria in our guts influence mental illnesses more than generally known. How are these two organs connected?

„The nerves of the gut and brain use messenger substances for communication: neurotransmitters. These are made from amino acids, the building blocks of proteins in our diet. A significant part of this conversion happens in the gut, partly done by bacteria. For example, the amino acid tryptophan is converted by gut bacteria into serotonin, a neurotransmitter active in both the gut and brain."

How can these bacteria affect diseases?

„Take dopamine, central to Parkinson's disease, made from the amino acid tyrosine through several conversions. We're now discovering that gut bacteria are also involved in breaking down medications. For instance, Levo-dopa, a common Parkinson's drug, is largely broken down in the gut by some people, reducing its efficacy. This depends on their gut microbiome's composition. We believe this could apply to other medications as well. My team is currently investigating the breakdown of antipsychotics in the gut."

The gut flora also plays a role in stress management. What are the new scientific insights?

„Recent research shows that stress is more connected to the gut than it first appears. In these studies, a small mouse in a cage feels intimidated by a larger mouse. Repeating this leads to the small mouse experiencing social defeat. It gives up, loses interest in sugar water or meeting other mice. These are termed 'broken' mice. Some mice are more affected than others. Interestingly, the 'unbroken' mice have a specific strain of lactobacilli, found in cheese and milk, in their guts. When the 'broken' mice received this strain, they also became less vulnerable."

Can we apply this to humans?

„Humans can also exhibit 'broken behaviour' due to prolonged stress, like burnout, depression, or anxiety disorders. Possibly, this can be prevented by strengthening gut bacteria. A study in Japan gave medical students entering a stressful exam period probiotics, while a control group received a placebo. The probiotic group indeed experienced less stress and fewer stress-related stomach issues than the placebo group. Unfortunately, the study didn’t investigate or mention whether this also improved their study results. It’s promising to consider enhancing stress resilience by improving gut flora."

You previously researched schizophrenia and hearing voices. How did you become interested in the gut?

„As a psychiatrist, I'm always looking for ways to do more for patients. Improving the bacterial environment in the gut is a non-invasive way to positively affect the brain. You can easily access gut flora through dietary interventions and probiotics, and by eliminating bactericidal food and medication."

You earlier spoke about the elevated status the brain once held. Do you face resistance in practice to the idea that gut bacteria influence the brain?

„Sometimes. People are convinced that we're self-acting entities with free will. We think we're different from mice, as we have a soul and consciousness. Yet, the significant differences at the brain level between humans and other mammals are not as pronounced as one might think. While mouse research doesn't translate directly, humans do have mammalian brains influenced by hormones, neurotransmitters, and the immune system, not so different from mice. It’s arrogant to think our brains are vastly superior to those of other mammals."

We've mostly talked about the positive role gut bacteria can have on the brain. What about the potential negative impact of chronic gut conditions?

„Patients with gut disorders often suffer from depression and anxiety disorders. Take a condition like Irritable Bowel Syndrome (IBS), where half of the patients have a psychiatric condition. This isn’t coincidental. The same messenger substances are active in both organs. Antidepressants are effective for IBS; they can also alleviate gut symptoms."

What do you do to keep your brain healthy?

„I eat quite healthily. I cook with fresh ingredients and avoid ready-made meals. I also drink fermented products like water kefir or buttermilk. Beneficial bacteria thrive in acidic environments. I drink as little alcohol as possible. We know alcohol is harmful to the brain, but it's equally damaging to the gut. In the hospital, we use alcohol as a disinfectant. It has the same effect in your gut. Consuming a significant amount of alcohol kills your gut microbiome."

„But if I can give one piece of advice: the most important thing you can do for your health is not to smoke. Smoking is detrimental to all organs, especially the brain. So, the best thing you can do for your brain is to quit smoking. If you're already a non-smoker, then healthy eating and cutting out alcohol are excellent next steps to increase your chances of ageing healthily."