- Our gut microbes moderate our mood via the gut-brain axis.
- The food we eat alters our gut microbial profile.
- A Mediterranean-style diet can improve our perception of stress.
Our lives are stressful, and thanks to pandemics and politics, it seems to get worse by the day. That stress slowly gnaws away at our mood and health, making anxiety and depression the leading causes of disability worldwide.
But there is a light on the horizon. Thanks to the indefatigable efforts of John F. Cryan, Ted Dinan, and colleagues at University College Cork, we now have a way to stiffen our resilience to the stressors of life. Astonishingly, there are no drugs or surgeries involved. If you can handle a few changes to your diet, you can start to take life’s pressures in stride.
In 2013, Cryan and Dinan published a study identifying a set of microbes that could improve mood. They dubbed them psychobiotics. Full disclosure: Soon after that article, I started to work with them on a book called The Psychobiotic Revolution. They have never stopped impressing me with their dedication to this pioneering research. They had to overcome major headwinds from researchers who strongly doubted that microbes in the gut could affect the brain. Today, the gut-brain axis is widely recognized, but it was heresy just a decade ago.
Most of the early work was done with mice, which can be bred in germ-free environments, a major advantage when trying to isolate the effects of microbes. But there was a paucity of research on humans. Over the years, that mouse-orientation has been addressed, and several psychobiotics – both microbial and prebiotic – have now been studied in humans.
The new study
With their new study, Cryan and Dinan have added a new tool to the psychobiotic toolkit. Instead of supplements, they looked at diet as a way to improve the gut-brain axis, and they struck paydirt.
Their study took 45 healthy adults and put them on a placebo diet or a psychobiotic diet. After one month, 17% on the control diet showed improvement in perceived stress, but 32% on the psychobiotic diet showed improvement, almost twice as many. The higher the adherence to the diet, the better the improvement.
The authors point out that although observance of the psychobiotic diet was pretty faithful, ferments proved challenging, with most people managing only half of the recommended servings. Ferments are both prebiotic and probiotic and are a major component of a psychobiotic diet, so this was a potential shortcoming of the study.
The control diet adhered to the Healthy Eating Guidelines, which represented a step up for most people, accounting for their improvement during the study. There were some mysteries in the data as well. For instance, changes in the microbiota were subtle, but there were significant changes in metabolites – the products of gut microbes.
Despite these minor shortcomings, the study's findings are significant, and the authors conclude that, “given the fundamental influence of stress on the risk for developing other chronic diseases such as depression, these findings hold promise as potential therapeutic and preventative approaches.”
One thing to note: The reduction of stress was only observed during the study; it vanished afterward. Thus, the psychobiotic diet is not a cure, but a therapeutic lifestyle: You must continually feed the good bacteria for your brain to maintain the benefit.
How do psychobiotics work?
There are many different ways for microbes to affect the brain, including nerves, hormones, and immune agents. Importantly, psychobiotic microbes reduce inflammation, allowing the brain to chill out.
One important pathway is the restoration of a damaged gut lining. A normal gut must be permeable to allow for the absorption of nutrients. But an overly permeable or “leaky” gut may allow toxins or bacteria to find their way into the bloodstream, where they get pumped to every organ in the body, including the brain.
Our immune system is capable of mopping up these vagabonds, but only to an extent. If the infection is strong enough or persistent enough, chronic inflammation can set in. The brain responds by initiating sickness behavior, which is mostly indistinguishable from anxiety and depression. However, in this study, the subjects were all healthy and had no obvious gut issues. The strongest gut-brain candidate here was metabolic — in particular, tryptophan and lipid metabolism.
What is a psychobiotic diet?
There are two parts to every diet: foods to avoid, and foods to include. Let’s look at the unhealthy foods first. A psychobiotic diet forgoes fast food, highly processed food, and sugary food. These all promote bacterial growth of the wrong kind and in the wrong places.
Now for the healthy foods. You should add whole grains and fermented food as well as fiber-filled veggies, fruit, and beans. If this sounds familiar, it’s because it is akin to a Mediterranean diet, which scores highly on the psychobiotic scale.
From the article, the psychobiotic diet “included consumption of fruits and vegetables high in prebiotic fibers (6–8 servings per day, e.g., onions, leeks, cabbage, apples, bananas, oats), grains (5–8 servings per day), and legumes (3–4 servings per week) ,as well as fermented foods (2–3 servings per day, e.g., sauerkraut, kefir or Kombucha).”
Yes, that is a lot of servings, and almost none are available at Mcdonald's or Burger King. However, a good salad typically contains several servings of veggies, and it is easy to add grains like brown rice or whole-wheat bread to any meal. The proof that it is eminently doable is that people around the Mediterranean have eaten like this for centuries – and a disproportionate number of them are centenarians.
If you have a demanding life, this study shows that simply changing your diet can improve your perceived stress. Luckily, it’s easy to love a Mediterranean diet. Embracing new eating habits is a small price to pay for some peace of mind. You might want to give it a try.
Berding, Kirsten, Thomaz F. S. Bastiaanssen, Gerard M. Moloney, Serena Boscaini, Conall R. Strain, Andrea Anesi, Caitriona Long-Smith, et al. “Feed Your Microbes to Deal with Stress: A Psychobiotic Diet Impacts Microbial Stability and Perceived Stress in a Healthy Adult Population.” Molecular Psychiatry, October 27, 2022, 1–10.
Kawano, Yoshinaga, Madeline Edwards, Yiming Huang, Angelina M. Bilate, Leandro P. Araujo, Takeshi Tanoue, Koji Atarashi, et al. “Microbiota Imbalance Induced by Dietary Sugar Disrupts Immune-Mediated Protection from Metabolic Syndrome.” Cell 0, no. 0 (August 29, 2022).