The gut-brain connection: can eating the wrong foods make you unhappy?
10.7.2026
Translation: Katherine Martin
In his new book, «Das Psyche-Darm-Paradox» (The Mind-Gut Paradox), nutrition expert Matthias Riedl explains how your diet, gut microbiome and brain are connected.
Ever since the release of Gut, the surprise bestseller written by then-medical student Giulia Enders, people have been catching on to the fact that our digestive systems do more than just mechanically break down food. It’s a realisation that’s sparked a veritable boom in gut health guides, covering everything from how the digestive system works (The Good Gut), to gut health advice and gut-friendly recipe books («Iss deinen Darm gesund», «Medical Cuisine – Gesunder Darm»), to books focused on specific conditions like irritable bowel syndrome and inflammatory bowel disease («Der Darm-Doc»).
Nutritionist Matthias Riedl, known in the German-speaking world as «Ernährungsdoc» (The Food Doctor), has built on this with his new book «Das Psyche-Darm-Paradox» (available in German only), shifting the focus away from digestion alone and towards the mind. Why does an unhealthy diet affect our mood?
The gut-brain paradox
Your gut doesn’t just digest food. It’s home to a complex system of nerves, immune cells and microorganisms that regulates far more than just food digestion. This system uses the gut-brain axis (link in German) to stay in constant communication with the brain via nerve pathways, hormones, immune processes and bacterial metabolites. The vagus nerve, the most important nerve connecting the digestive tract to the brain, plays a special part in this process. It’s only in the last few years that science has started to gain a more precise grasp of just how closely the gut, the microbiome and the mind are connected.
The paradox that Riedl lays out in his book? Highly processed foods, which provide a short-term sense of comfort or reward, can actually worsen mood, sleep and cognitive function in the long run. He attributes this to a combination of microbiome disruption, silent inflammation, blood sugar fluctuations and a reward system repeatedly triggered by processed foods. That comforting piece of chocolate may give you a quick dopamine boost, but in the long run, it’ll negatively affect your microbiome, which in turn can impact your mental health. In the book, Riedl traces this connection all the way to depression, anxiety and ADHD.
Despite our abundance of food, we’re silently starving
Yes, we eat enough (if anything, too much), but we’re eating the wrong foods. We basically experience excess and deficiency at the same time, consuming loads of sugar, fat and calories, but not enough of what the body actually needs: protein, fibre, vitamins and minerals. According to Riedl, this is the modern diet’s core problem. Although it makes you feel full in the short term, it does even less to nourish your body than you might expect from a frozen pizza or a chocolate bar. This is called «silent starvation», a phenomenon that changes the composition of bacteria in your gut.
How a healthy diet protects your mental health
The second part of the book gets down to the specifics. Riedl explains seven basic nutritional principles that, if followed, strengthen the gut and, by extension, the mind. These include reducing your sugar intake, avoiding highly processed products and setting fixed breaks between meals. Detailed profiles of highly recommended foodstuffs, such as oatmeal, broccoli and turmeric, round out the information. However, Riedl’s guide isn’t a cookbook. If it’s specific recipes you’re hoping for, you’ll be disappointed. Though Riedl does refer readers to his previously published recipe books.
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The idea that your diet can significantly impact your mental health is given much more weight today than it was just a few years ago. If you want to delve deeper into the topic while getting an easy-to-understand explanation of how nutrition, the gut and mood are connected, «Das Psyche-Darm-Paradox» is an accessible way in.
Header image: Ekaterina Byuksel/Shutterstock
Anna Sandner
Senior Editor
Anna.Sandner@galaxus.deScience editor and biologist. I love animals and am fascinated by plants, their abilities and everything you can do with them. That's why my favourite place is always the outdoors - somewhere in nature, preferably in my wild garden.
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