The Link Between Stress and the Microbiome: New Research Explained

How does psychological stress impact gut health? And how can we use new science, new knowledge to improve our gut health and our mental health? These are the questions I'm going to try to answer today. So if you or someone you know has ever suffered from bloating, constipation, or GI upset, which I think covers most people, you will want to watch this video all the way through. Now, in this video, I promise you: 1. Specifics. I'm not gonna wave my hands and use generalist terms, but speak about specific causal cascades linking brain to gut and gut to brain based on new and exciting science. 2. I'm gonna offer you actionable takeaways and practices that I myself am going to try to implement because, in truth, This is one video I'm making as much for myself as I am for you. Okay, let's get into the data. The paper in question was just published in Cell, one of the top journals in the world, and is entitled "Stress-Sensitive Neural Circuits Change the Gut Microbiome Via Duodenal Glands." The duodenum being part of the small intestine. At a high level, the researchers discover a pathway whereby activity in a brain region associated with stress and emotions, the amygdala, controls the vagus nerve, the 10th cranial nerve, that connects the brain to the gut and the gut to the brain. And in so doing, the brain can toggle the activity of glands in the intestines called Brunner's glands that make mucin that feeds the microbiome. Which can in turn influence GI symptoms and gut health. So again, at a high level, the brain talks via the vagus nerve to Brunner's glands in the intestines that make mucin that feed the microbiome, and this can impact gut health and in a reciprocal fashion impact brain and mental health. Now let's look at some of the data together. Now I do say some of the data because there are 163 figure panels in the main text alone. That's not even including the supplement. I know, right? 163. And if I went through all of these, I think we'd be here for about 18 hours, and I'd probably stress you out, which, as you will learn, can have a negative material effect on your gut health. So let's first introduce the leading gut bug in our story: Lactobacillus. Now, there are actually many different species in the genus Lactobacillus, but for the sake of simplicity, consider Lactobacillus good guy gut bugs. They're common probiotics and also the primary genus found in many considered to be healthy fermented foods like yogurts, sauerkraut, kimchi, and so on. Shown here, the researchers found that by stimulating mucin-secreting Brunner's glands In mice, the Brunner's glands provided nourishment to lactobacillus to promote their growth. However, surgical removal of these Brunner's glands negated this effect and depleted lactobacillus levels. So this shows that mucin-secreting Brunner's glands are important for promoting lactobacillus growth. But the question: what controls Brunner's glands? Well, they found the vagus nerve directly connects the brain to the gut, and specifically connects the brain to Brunner's glands. So if you cut the vagus nerve, the brain can't activate Brunner's glands, and lactobacillus are depleted. So the brain is what's controlling Brunner's glands, along with peripheral hormones. But now, the vagus nerve, what is it? It's involved in parasympathetic, rest and digest nervous system activity. This is in contrast to the sympathetic fight-or-flight branch of the autonomic nervous system. So high level, we start to form this picture whereby calming vagal parasympathetic rest and digest nervous system activity activates Brunner's glands. And if you want specifics, it's through releasing acetylcholine, a neurotransmitter, onto M3 muscarinic receptors, if you want the details. But this increases mucin production from Brunner's glands to feed and proliferate Lactobacillus. And this is consequential because the microbiota in your intestines can directly, and through reciprocal activities on the nervous system, alter gut function and gut symptoms. In fact, if you knock out Brunner's glands or you cut the vagus nerve connection to Brunner's glands, this can lead to severe gastric bloating, as you can clearly see here. It's quite profound. And it can also lead to leaky gut, increased gut permeability, and heightened immunoreactivity. Now, let's complete the picture by adding the master controller to the system, the brain. They found, the researchers found that one critical brain region, the central amygdala, which is the core of an almond-shaped brain center involved in emotions and stress response, was the master regulator. Indeed, The researchers found that activation of the central amygdala enhanced signaling through the vagus nerve and thus increased Brunner's gland activity to lead to increased lactobacillus and improved gut function. So in this way, the central amygdala in the brain associated with your emotion directly controls the microbiome, which is freaking fascinating. And they show that stress inhibits the central amygdala, and that stress lowers Lactobacillus levels. Thus, zooming out once again, stress inhibits a brain region, leading to decreased signaling to mucin-secreting glands, Brunner's glands, starving the good guy gut bacteria. And while you can't exactly do these causal mechanistic experiments in humans, these data are very likely relevant to humans. As it's been well documented, shown previously, that stress is associated with reduced lactobacillus in multiple primate and human studies. But going well beyond this correlation in humans, the researchers actually did something quite brilliant in my opinion. They studied surgery patients who had a region of their guts removed, the region containing Brunner's glands. Specifically, they took patients who underwent surgery for non-metastatic gastrointestinal stromal tumors. And what they did was they compared those who had the region of the intestines that contains Brunner's glands to other patients who had similar tumors but who had surgery with a slightly different part of the intestines removed so that Brunner's glands were actually preserved. So you get this really interesting comparison. It's ingenious. And indeed, they found immunological changes consistent with the mechanistic data shown in this paper. Now, this is somewhat an aside, but I think it's a brilliant example of how you can couple rigorous causal animal mechanistic models with observational data in humans and natural experiments in humans to demonstrate that the former, the mouse studies, are most probably relevant to the latter, human studies. So in summary, these data are consistent with a model whereby the central amygdala in the brain signals through the vagus nerve to increase secretions from Brunner's glands, which feed Lactobacillus, leading to better gut barrier function, better autonomic tone, less GI upset, less bloating, and overall better GI function. Conversely, stress decreases signaling from the central amygdala to Brunner's glands, thus depleting lactobacillus, starving them off, leading to bloating, leaky gut, among other unfortunate effects. Now, really quickly, before getting into the actionable takeaways that I promised you, astute viewers might have noticed that stress equates to less central amygdala activity, even though the amygdala is often thought about as the fear, fight, and flight region of the brain. So this might seem counterintuitive if you're following, but basically, brain regions are heterogeneous, with different neuron populations that carry out many different jobs. So I wouldn't take this as a paradox, just a complexity. And if that went over your head, ignore this last bit, but I did just want to mention that for the uber neuro nerds out there. Now, what can you do to leverage this new knowledge to intervene on this pathway to improve your gut health? Well, perhaps the most actionable and inexpensive modality is through stress reduction exercises. This includes deep breathing, physiological sighs, yoga, meditation, or just doing whatever relaxes you. Now, on the physiological sigh front, this is a technique brought to my awareness and popularized by Professor Andrew Huberman. Involves a specific pattern of breathing that activates the parasympathetic nervous system, and it consists of a double inhale followed by a long exhale, like, "Sniff, sniff, exhale." And I'll link to more information on that below. And on the user-specific relaxation technique, I want you to seriously contemplate what relaxes you. Often this falls into the category of guilty pleasures. And if you're anything like me, type AAA, you may even avoid these activities by virtue of the fact that they aren't classically productive. However, in sharing the data presented in this video with you, I want you to contemplate that what might not seem productive may actually be productive insofar as it's good for your gut health and by knock-on effects, your metabolic health. So yes, that means, for me, taking myself as an example, I can rationalize curling up on the couch in a ball and binge-watching Game of Thrones or Marvel movies as a metabolically healthy intervention. What do you think of that? Kind of a nice free pass to enjoy yourself, right? But seriously, enjoyment, relaxation, social connection, these are all really important to gut health and metabolic health and mental health, of course. In addition, Consuming fermented foods containing lactobacillus may be beneficial consistent with this literature, including things like sauerkraut, kimchi, pickles, yogurts, and so on. I personally really enjoy kefir. Now, let me know your thoughts, let me know if this was helpful, what you liked about this video, what you didn't like, and as always, stay curious, and I'll see you in the next video.