In my recent article entitled 3 Things You Probably Didn’t Know Gut Bacteria Can Do I made the case that the bacteria that colonize our bodies play a role in shaping our dreams. In the time that has passed since I put up that article, I’ve been thinking more about the microbiome-host dreaming phenomenon, and I’ve come to the conclusion that gut microbiota composition is probably the main factor responsible for determining the nature of our dreams. This is something I believed at the time when I wrote the aforementioned article as well; however, I didn’t come out and explicitly said it. Gut bacteria undoubtedly also play a role in shaping the dreams of many other eukaryotic, multicellular organisms that live here on Earth.
The idea that gut bacteria shape our dreams isn’t just fascinating and interesting from a theoretical point of view; it has some potential practical implications. Your dreams can help inform you about the state of your microbiota; hence, they may help guide you towards better health.
The gut: A dream factory?
Perhaps needless to say, the statement that microbes exert control over our dreams doesn’t have a big pile of scientific data to rest on. Nor a small pile for that matter. The reason is not that studies have found the statement to be incorrect, but rather that no good studies have specifically looked into how gut bacteria affect our dreams. It doesn’t take a genius to figure out why this is the case. It’s obviously very difficult to assess how the invisible life forms that dwell deep down in our guts affects what goes on in our heads when we sleep and how different types of organisms impact what we dream about.
With that said, as I pointed out in my earlier article on this topic, the aforementioned statement does have a solid body of anecdotal reports behind it. Moreover, it is supported by some indirect mechanistic evidence. These types of data may not be as powerful as those derived from clinical trials with respects to the generation of causal conclusions; however, they do provide us with information that we can use to make educated guesses and generate hypothesis.
In today’s article, I’m not going to repeat the things I talked about in my last article on this topic (If you haven’t already read it, I suggest that you go back and do so now, before you continue reading this one). What I thought I’d do instead is to briefly look into some facets of the microbiome-host dreaming connection that I didn’t get around to exploring the last time around.
Over the years, I’ve not just been paying attention to what other people have reported with respects to how they feel their gut bacteria affect their dreams, but I’ve also paid attention to the impact that the microbes that colonize my own body have on my brain – both when I’m awake and when I’m asleep. This process, in conjunction with the process of looking into the biological mechanisms that play a role in dreaming, has left little doubt in my mind that gut bacteria exert a profound control over what goes on in the human brain during sleep. It’s well established that the bacteria that colonize our bodies affect what goes on in our heads at day – our thoughts, mood, and behaviors (1, 2, 3). I see no reason to think that this doesn’t also happen at night. The human gut may be a dream factory; a factory that employs trillions of tiny workers.
Having nightmares? Your microbiota may be to blame
One of the things that has become clear to me is that gut dysbiosis can cause nightmares. Dysbiosis is obviously not the only thing that can bring monsters into our heads at night; scary movies, traumatic life experiences, and many other things can as well. With that said, dysbiosis is probably a very common cause of nightmares.
I’m quite certain that it’s not just severe, chronic dysbiosis that can cause a person to have bad dreams; transient disturbances (both mild and severe) of the gut microbiota can as well. If you’ve ever eaten food that has gone bad and as a result ended up spending the next day chained to the toilet, then you’ve probably experienced this for yourself. Many different types of microorganisms and parasites are known to have evolved a capability to affect the behavior of larger organisms such as ourselves (4, 5, 6, 7). They do so via their metabolic activities and their production of various fatty acids, neurotransmitters, and other compounds that can enter the systemic circulation of potential hosts.
Besides believing that many types of unfriendly gut bugs can cause us to have bad dreams, I’m convinced that our gut microbes exert a lot of control over the intensity, vividness, and duration of our dreams. As I pointed out in my earlier article on the gut microbiome-host dreaming phenomenon, there’s a wealth of anecdotal reports that support this idea. I’m willing to guess that it’s also supported by your own experiences.
If there’s ever been a day where you’ve eaten a lot more fiber-rich foods than you usually do, you may have noticed that your dreams the following night differed from those you have a typical night. Resistant starch, inulin-type fructans, and other fermentable compounds are well known to have dream-inducing properties. Not only do they seem to promote dreaming, but they seem to make our dreams more intense and vivid.
You don’t have to take my word for it. You can easily determine if it’s true for yourself; just head down to the grocery store; buy a couple of onions and some slightly green bananas and potatoes; head on home and cook the potatoes; leave the potatoes in the fridge for a day so that their content of resistant starch increases; cook the onions; and then sit down and eat it all. If you do so, I’m willing to bet that you’re going to have some pretty crazy dreams the following night.
Keep in mind: This is an experiment; it’s not something I recommend doing on a daily basis. While it’s certainly good to consume fiber, it’s not wise to overwhelm the gut with massive amounts of resistant starches and fructans, at least not on a regular basis.
I’ve been trying to wrap my head around the question of whether there is any evolutionary significance to all of this. There undoubtedly is; however, I haven’t been able to clearly pinpoint it. One idea that’s been circulating in my head is that some of the actors in this dream theater attain some sort of fitness benefit.
The primary reason why some types of microorganisms, as well as parasites, have evolved an ability to manipulate the behavior of potential hosts is likely that it gives them an edge in the evolutionary arms race. You don’t have to have a PhD in biology to understand why this would be the case; all you need is a basic understanding of how evolution works.
Let’s say that one of the microbes that colonize your body is capable of producing substances that can enter your body, travel to your brain, and impact your thoughts and behavior in such a way that you feel a desire to eat foods that contain compounds that the microbe in question is capable of breaking down and deriving energy from. Such a microbe would obviously have an advantage when put against a microbe that hasn’t evolved a similar ability.
Is it just pure speculation that something like this can happen? No! As pointed out earlier, there is solid scientific data supporting the idea that many types of microorganisms and parasites can manipulate the behavior of larger organisms.
The question becomes: Do the organisms that colonize our bodies attain any fitness benefits from manipulating our dreams? It’s possible. Interesting and vivid dreams may act as a signal that reinforces certain types of behaviors. For example, if an animal always gets vivid and fascinating dreams after it consumes significant quantities of foods that contain specific types of fermentable compounds, it may be compelled to continue consuming the foods in question; as long as it’s able to make the connection – whether unconsciously or consciously – between the food its eating and its dreams, of course. If the dreams indeed trigger the animal to continue with the same eating behavior, that would obviously benefit the microbes that derive energy from the fiber-rich foods the animal is eating.
It could also be that the host benefits. In the case of fiber consumption, the interests of fiber-loving microbes and animal hosts are often aligned. For example, when we humans consume fiber-rich foods, it’s not just the fiber-loving varieties of bacteria in our guts that benefit, but also us. As they break down fiber, gut microbes produce Short-Chain Fatty Acids (SCFAs) and various other substances that we – the human hosts – can derive energy from.
Not only do we derive energy from SCFAs, but these compounds are also known to play important roles in many of the processes that take place inside of our bodies, some of which are related to immune functions (5, 6). They probably also affect our dreams, as I pointed out in my previous article on gut bacteria and dreaming.
The fact that these compounds play such an important role in many bodily processes could lead one to speculate that various apparatus that regulate our intake of SCFAs have evolved. Dreaming could play a role in all of this in the sense that dreams may, as previously pointed out, act as signals that reinforce specific types of behaviors. If the vivid dreams that follow the consumption of fiber-rich foods reinforce the consumption of fiber-rich foods, that may benefit the host in question in the sense that he continues to get a lot of immune-stimulating, energy-containing SCFAs into his system on a regular basis.
If our dreams do indeed impact our behavior or actions in such a way that our fitness is affected, then that would mean that mechanisms that regulate dreaming has probably been subjected to the forces of natural selection. Evolution may have acted in such a way that “good dreams” are produced by behaviors that benefit our survival and reproduction, seeing as this could trigger us to re-engage in those behaviors, whereas “bad dreams” are produced by behaviors that undermine our survival and reproduction (e.g., the consumption of pathogen-containing foods).
These mechanisms (if they exist) can probably be overridden by certain types of environmental stimuli though. In the above scenario, it’s not just the human host that benefits, but also the gut microbes. The fiber-loving microbes in the host’s gut benefit in the sense that they get dinner every day. In other words, in this scenario, both microbes and host benefit.
This is not always the case though. Sometimes, the interests of the host conflict with that of the microbes. For example, to a human host, it may not be advantageous to eat a lot of sugary foodstuffs on a regular basis, as that behavior may make him fat, sick, and tired, all of which may compromise his Darwinian fitness. However, from the perspective of let’s say sugar-loving oral bacteria, it’s obviously good to have a regular influx of sugar.
This comes back to something I’ve been talking a lot about here on the site (e.g., here, here): The link between diet, microbiota composition, and food cravings. The consumption of unhealthy foods can trigger the development of a vicious cycle in which “bad” gut bacteria flourish and undesirable food cravings appear (And bad dreams as well?). The consumption of healthy foods, on the other hand, sets the stage for the development of a virtuous cycle in which friendly gut bacteria thrive and healthy appetites – and perhaps also good dreams – prevail.
There is no doubt in my mind that the microbes that dwell in our guts affect our dreams. What I’m not certain of, however, is where dreaming fits into the microbiome-host eating behavior/body fat regulation puzzle. The thoughts I’ve shared in this article with respects to the evolutionary significance of the microbiome-host dreaming connection is just that: thoughts. Some of the hypotheses I’ve presented undoubtedly need some fine-tuning. Also, there are probably other evolutionary mechanisms involved up in all of this besides the ones I’ve talked about. In a future article, I may look into those.
For now, I’ll leave you with the following practical takeaway: If you consistently sleep well and have good dreams, then your microbiota is probably in good shape. However, if you don’t sleep so well and frequently have nightmares, your microbiota may be in a sorry state and you should strongly consider taking steps to repair and diversity it. Also, perhaps needless to say, it’s always a good idea to limit one’s exposure to artificial light at night, stress down before bed, and sleep in a cool, dark room.