Translation of the Dutch text by Marjolein de Jong | 26 February 2026
You said in 2023 that the gut microbiome plays an important role in brain disorders. Where does the research stand now?
We recently completed a promising dietary study involving people with severe neurological conditions, such as Parkinson’s disease, bipolar disorder and schizophrenia. Participants first followed their usual diet for three months, and then a specialised anti-inflammatory diet for another three months, or the other way around, as it was a randomised study.
We delivered groceries to their homes and provided healthy recipes. In addition, they had weekly contact with a dietitian, allowing us to closely monitor what was happening at an individual level. This study is quite unique, because typically researchers compare groups that already have different lifestyles. If you eat healthily, for instance, you are also more likely to exercise, which makes it difficult to determine what exactly drives any effects.
What did the participants’ diet look like?
It is the BRAIN diet: Brain Anti-Inflammatory Nutritional Pattern, in which most animal proteins and fats are replaced with plant-based alternatives. Participants ate plenty of legumes, whole grains and around 400 grams of vegetables per day, spread across different meals. In addition, they consumed three portions of fruit daily, yoghurt to support gut bacteria, and fish for its beneficial effects on the brain. Very little meat, in other words.
Why do you advise against eating meat?
We see that immune cells in our gut can recognise certain proteins found in meat, such as haemoglobin and myoglobin. These proteins closely resemble proteins in our own bodies that are released when tissue damage occurs. This triggers the immune system.
So when you eat meat from mammals that resemble us, the immune system may interpret these proteins in the gastrointestinal tract as a sign of tissue damage, increasing immune activity. This is unfavourable for people with gut disorders, but also for those with neurological conditions. In fact, it is not particularly healthy for anyone.
What results did the study yield?
The analyses are not yet fully complete, and the paper, in collaboration with Sophie van Zonnenveld and Toon Scheurink, is still to be published. However, we already observed that people with Parkinson’s showed clear improvements in symptoms such as fatigue, sleep problems and apathy. That is remarkable, as Parkinson’s is typically progressive and improvement is rarely seen.
How do you view the implementation of these insights in hospitals?
I am not entirely sure how things are organised nationally, but I suspect there is still much to gain. Good nutrition is crucial for recovery, yet hospital food is often prepared on a large scale and externally. That runs counter to fresh, locally prepared meals.
I recently visited a small-scale psychiatric clinic in Sweden, where patients and staff cook together. The entire process - shopping together, cooking, even enjoying the aromas - is considered part of recovery.
Is nutrition already included in treatment plans, for example in mental healthcare?
Not as standard practice, but I do see growing interest. I also notice that patients increasingly ask about it themselves. It is something people can actively do on their own, which gives a sense of autonomy. Healthy eating has not only a biological but also a psychological effect. When you cook well for yourself, you implicitly send the message that you are worth that effort.
You also conducted research among festival-goers at Lowlands. What did you hope to discover?
We asked festival visitors whether we could analyse their stool samples. In addition to the regular toilets on site., which are, of course, busy and not particularly clean, we built a clean and comfortable ‘dream toilet’. In exchange for completing a questionnaire and donating a sample, we were able to study their microbiome.
We found that people who scored high on neuroticism - meaning they tend to worry a lot, doubt themselves and feel anxious more quickly - on average had a less diverse microbiome. These individuals also tended to eat meat more than once a week, consumed too little fibre, and more often experienced abdominal pain.
What does that mean for people without a diagnosis, but who struggle with stress or sleep problems, for example?
That nutrition is not only relevant in the context of illness. It can also contribute to resilience against stress. If you tend to worry a lot or feel easily out of balance, it may help to reduce meat consumption and increase fibre intake.
What is the next step for you?
Knowledge about nutrition should become a structural part of treatment plans. I am not suggesting it should replace existing treatments, but it should certainly complement them. Hippocrates once said: “Let food be thy medicine.” As far as I am concerned, it is high time we started taking that idea more seriously again.
