TEDxMileHigh 2020

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Check it out: Spinach. Something you might have eaten hundreds of times. But did you know that on and inside this spinach plant, invisible to the human eye, there are more than 800 different species of bacteria? This isn’t about doing a better job of washing your veggies. These are bacterial endophytes, and you can’t wash them off, even if you try. Plants are living organisms, and, like us, they have microbiomes, thriving ecosystems of bacteria and other microorganisms.

I became fascinated by this fact about four years ago when I was collaborating on an article about the American Gut Project. They asked survey respondents, “In an average week, how many different plant species do you eat?” Responses ranged from 0 to > 30 plants in an average week. Nutritional guidelines are usually based on volume – like how many cups of fruit or veggies do you eat each day. But researchers found that variety matters just as much, if not more. The people who reported eating more than 30 different plant species per week had what we would consider an optimal gut microbiome with high diversity. Unfortunately, that’s not most of us!

So I thought to myself, what would happen if I consumed 30 different plants a day? It would be like eating a whole forest, or a farm, every day.

So, I went to the grocery store and picked out 30 different plant species, brought them home, rinsed them off, chopped them up, put them in a blender with six cups of water, and then had 30 different plants a day for the next month. Then I did it again, and again. These days, my nine-year-old daughter helps me. Finding 30 different types of plants in the grocery store can be a fun challenge – I end up trying all kinds of new things, like sorrel or raw cactus. I’ve decided it’s as close as I’m gonna get to living a hunter-gatherer lifestyle. I prepare this plant cocktail once a month & then have a serving every night for dinner. It has completely changed my life. 

Now, at this point, you might think I’m some kind of nutrition junkie, but actually, I’m a neuroscientist, and I specialize in anxiety disorders, affective disorders, like depression, and trauma- and stressor-related disorders, like posttraumatic stress disorder or PTSD. 

Mental health has become a hot topic in the last few months and with good reason. A survey from the Census Bureau and the CDC found that, since late April 2020, about a third of Americans have reported recent symptoms of anxiety and depression, which is much higher than in previous years. We desperately need new ideas to solve our mental health problems at scale. 

The reason I’m so interested in this plant cocktail is not necessarily because it’s nutritious (although it is) and definitely not because it tastes good (you might think that it doesn’t), but because of the way these BACTERIA affect our mental health.

Whether you like it or not, sorry germaphobes, we breathe in and consume millions, maybe billions, of bacteria every day. We’ve known about the beneficial effects of bacteria on our health for decades now. There’s even a name for this idea – the “old friends” hypothesis.

If you think about it, the first mammals were tiny shrew-sized creatures that lived among dinosaurs and burrowed under the soil. This means that for at least 210 million years, mammals co-evolved with soil bacteria – burrowing in the soil, breathing soil, and eating soil. These bacteria truly are our “old friends,” and they communicate with our brains through what is called the microbiome-gut-brain axis. There’s also evidence for a microbiome-airway-brain axis, and both seem to be important for maintaining our physical and mental health. There are many ways bacteria help us out, from synthesizing vitamins to metabolizing fiber, but for this talk, what you need to know is that many bacteria can reduce inappropriate inflammation in our bodies.

For example, growing up on a farm can protect you from developing allergic asthma; in fact, that effect is so strong, and so highly replicated, that it’s just called “the Farm Effect”. A recent study compared children from Amish and Hutterite communities. These groups have a similar ethnic origin in Europe but have maintained different farming practices. Hutterite communities have adopted modern farming practices, including the use of tractors, whereas Amish communities have maintained the use of traditional farming practices, including the use of large farm animals to work in the fields. Compared to the average American child, Hutterite children have a low risk of allergic asthma, and Amish children have an even lower risk. Investigators took dust from the bedrooms of Amish children, exposed mice to the dust, and found that it modulated their immune systems in a way that prevents allergic airway inflammation. So what is it about farms and dust that protects us from inflammation? Again, evidence points toward exposure to a diverse microbial environment.

So what does this have to do with mental health? Well, most of the mental health conditions you’re familiar with – anxiety, depression, PTSD – can be caused by inflammation. If growing up on a farm can protect against allergic asthma, can it also prevent stress-induced inflammation and therefore, risk of stress-related psychiatric disorders?

In 2018, I partnered up with Professor Stefan Reber in Germany to test the idea that growing up on a farm may protect against inflammation and, therefore, the risk of stress-induced psychiatric disorders. We studied healthy young men. Half of the men grew up on a farm with farm animals for the first 15 years of their lives. The other half grew up in cities of over 100,000 people, without pets. We asked the participants to give a speech in front of a camera and a panel of scientists in white lab coats, which is, I kid you not, one of the most stressful things that we can do to humans to induce stress in the research laboratory. Trust me when I say giving a speech is stressful! Interestingly, the young men who grew up in cities had an increased inflammatory response to stress. This supports the idea that growing up on a farm provides stress resilience, and protects us from stress-induced inflammation, and the risk of stress-related psychiatric disorders. 

Ok, so how far can we push this? Could we strategically USE bacteria to prevent or treat psychiatric disorders? Twenty years ago, we injected mice with a dead bacterium called Mycobacterium vaccae, a bacterium that was isolated from the mud on the shores of Lake Kyoga in Uganda. We already knew that injections of M. vaccae could protect mice from developing allergic airway inflammation, and we wanted to see if injections with M. vaccae could also alter emotional behavior. In this study, immunization with the bacteria activated serotonin neurons in the brain. In addition, the mice behaved as if we had given them an antidepressant drug! When we published the study in 2007, this seemed really novel. But as we learn more about the microbiome-gut-brain axis, it’s not so surprising. 

This led to a recent study with Dr. Lisa Brenner and her amazing team at the VA right here in Denver, Colorado. We partnered with US Military Veterans with a diagnosis of PTSD and mild traumatic brain injury and gave them a live bacterium with anti-inflammatory properties daily for eight weeks. We then brought them into the research laboratory and exposed them to the same psychosocial stress that I described earlier. Those that received the anti-inflammatory bacterium showed reduced stress reactivity and a strong trend for reduced inflammation. Although larger studies are needed, it supports the idea that exposure to bacteria with anti-inflammatory properties can promote stress resilience.

I believe this research will open up a whole new world of opportunities for the prevention and treatment of mental health conditions. Already we’ve seen a new field developing – “nutritional psychiatry.” A meta-analysis in 2019 showed that whole dietary changes could reduce symptoms of anxiety in depression, both in healthy populations and in individuals who were clinically depressed. Instead of writing a prescription for a drug, for example, your doctor could write you a prescription for a specific diet to treat your anxiety or depression, or PTSD. Your doctor might also write a green prescription for exposure to nature, as is being done in other countries. We might even find 30-plant variety packs in the grocery store so that we can just bring them home and put them in the blender. In the future, we may even develop a forest in a pill, a farm in a pill, or a shot to replace what we’ve lost by moving away from nature & living in cities. 

Although the research on bacteria & mental health is still a work in progress, you can take advantage of this knowledge now. There’s a big difference in the microbiome between someone who eats 5 plants relative to someone who eats 10 plants or 20 plants, or 30 plants in an average week. You can literally eat your way to better mental health. Add new plants to your cart at the grocery store – take the 30 plants a week challenge. Make it a competition with your friends or family to see how many different plants you can eat each week. Trust me, it’s not that hard to reach 30 different plants each week! Get yourself and your family outside in nature as much as possible, grow a garden, put plants in your house, get a dog! Pets are a great way to bring bacteria into your home, and I mean that in a good way!

We’ve long known about the restorative effects of nature on our mental health – but perhaps it was more than fresh air and sunshine at play.

It makes us wonder, was the future of mental health right under our feet, all along?

Thank you.

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