“You are not a drop in the ocean. You are an entire ocean in a single drop.” - Rumi
Prior to air conditioning, trees were planted around buildings in public housing units to provide shade and a place to cool off from the summer heat. Over the years, shifting policy decisions led to the removal of many of these trees as green spaces were paved over to save money on ground maintenance. There was also a belief that crimes were more likely to occur in areas where trees and bushes provided cover for drug dealing, break-ins, assaults, and robberies. With budget cuts and soaring crime rates, by the 1990’s, green spaces in public housing projects were paved over, transforming the area into a bleak landscape of unattractive buildings surrounded by concrete and small patches of grass.
Since 2001, University of Illinois researchers Frances Kuo and William Sullivan have helped to turn the tide on decades of public policy with their research related to green spaces, crime rates, and people’s well-being. They have amassed years of research showing that trees do more than just provide shade to a densely populated area. In some of Chicago’s public housing projects, they show that trees are correlated with lower crime rates and improved mental health of the residents. They found that residents who lived in buildings with trees around them were less likely to be victims of crime than those who lived in buildings without them. Kuo and Sullivan found that the lush environments provided by trees and other vegetation act as inviting communal space; 83% more residents socialized in these spaces than did those living in barren developments. Neighbors who gathered in these green spaces developed stronger bonds, resulting in more vibrant communities, which not only reduced crime rates but improved residents’ overall sense of connectedness and well-being.
As Kuo and Sullivan’s research into Chicago’s public housing shows, being in and around nature helps us develop a greater sense of cohesion and unity with others. Other studies have confirmed their findings, showing that even short periods of being in nature can foster a stronger sense of connection with others. Since natural surroundings have been shown to reduce stress after even short periods of exposure, some of the enhanced sociability is attributed to nature’s ability to shift our moods, resulting in less depression, anxiety, and rumination. In essence, nature can elevate our outlook, making us more likely to interact and be social with others. Living in green environments is good for our communities as well as our own individual mental health.
Whereas being outdoors in nature is an attractive and simple way to elevate our mood, there is a good deal of research that points to an underappreciated and frequently overlooked part of nature that is just as effective, and perhaps even more important, for our mental health. This aspect of nature is one with which we are so closely aligned that we may fail to even understand how strongly it impacts our health. Unlike trees, mountains, and rivers, these natural organisms are microscopic, and they can be found everywhere. These are nature’s microbes, the microorganisms that are responsible for half the weight of living matter on Earth, existing in all kinds of conditions, and eating anything. The human body is host to millions of these microbes which include bacteria, fungi, viruses, and yeasts, just to name a few. They are so pervasive that scientists estimate that for every human cell there is a microbe; they are found in so many places on the human body and their populations are so dense that collectively they weigh a few pounds.
Most of us are familiar with how microbes can keep us healthy as well as make us sick. We may have taken a probiotic to help restore balance in the gut after a round of antibiotics. But we may not be as familiar with how these microbes can affect our mental health, changing our mood, as well as our ability to learn, process our memories, and prevent serious psychiatric disorders. There is also a growing body of evidence that microbes play an important role in Parkinson’s disease, Alzheimer's disease, and other forms of cognitive decline.
The microbes that have the greatest impact on our moods take up residence in the gut. What we know about gut microbes is limited, but what we do know is overwhelming and not yet fully understood. We’ve known for a long time that the brain influences the functioning of the gut; Pavlov’s dogs showed us that ringing a bell can make us salivate even without the presence of food. The idea that our gut can influence our brain is a new concept, but one that is supported with continued research into what these critters do and how they impact our health. Scientists recognize that there is a gut-brain axis through which the gut microbiota affects almost all our bodily functions, including immunity, hormonal balance, cravings, sleep, the inflammatory response, and digestion. They are involved in a wide scope of our body’s functions. Not only do they produce vitamins and minerals, but they also produce neurotransmitters that impact our moods, such as serotonin and dopamine. New research is expanding our understanding of the important role they play in our mental health; that a microbe can influence how we feel may seem hard to believe, but the evidence seems to suggest that this may be closer to the truth than we’d like to believe. You might keep this in mind the next time you ask a cranky family member “What’s bugging you?”
Gut microbes work hard to earn their keep as residents and are dependent on the foods we eat to keep our systems running properly. Fiber is their preferred food source; when we don’t eat enough vegetables, fruits, whole grains, and beans they are forced to turn to other sources of sustenance. Without sufficient fiber, gut microbes start to digest mucin, a substance that forms the protective mucus layer lining the large intestine. Chronic shortages of fiber will force the gut microbes to eat this mucin layer, which eventually changes the permeability of the cell junctions in the walls of the intestine. When this happens, bacteria and food molecules from the gut enter the bloodstream, triggering an immune response which can reach the brain, creating a state of neuroinflammation. This sets the stage for increased feelings of anxiety, psychological distress, and rumination; several studies have correlated chronic inflammation due to gut permeability with the development of both major depressive disorder and schizophrenia.
A healthy gut has a good deal of diversity. The more our food choices come from natural sources and the wider the selection of whole foods we eat, the more our gut flora will flourish. Studies have found that people who eat a wide variety of vegetables, fruits, whole grains, and nuts tend to report more days experiencing elevated moods and fewer days of psychological distress. They also tend to be more sociable, connected, and generally report greater satisfaction in life. Of course, these are correlations and do not suggest that serious mental health concerns can be erased simply by eating a healthy diet. Rather, it shows that a diverse and flourishing gut can serve as a protective factor for our mental health, helping to maintain proper brain functioning, and providing support when we are faced with emotional upsets. In addition to producing the neurotransmitters serotonin and dopamine, gut microbes make short-chain fatty acids, substances that are produced when gut microbes break down the indigestible dietary fiber in our diet. Short chain fatty acids play an important role in brain functioning as they spur the growth of dendrites and synapses in the brain, both of which are essential to our ability to learn and access long term memory. Age related cognitive decline, Alzheimer’s disease, depression, and other mental disorders are associated with lower levels of short chain fatty acids, as well as less diversity in the composition of gut bacteria.
Since 2014, a growing number of studies are emphasizing the role diet plays in our mental health, consistently linking gut health, a whole food diet, and mood regulation. Yet Americans still get about 60% of their daily calories from highly processed foods. Recent studies have shown that the more ultra processed foods a person eats, the more likely they will feel depressed and anxious. Although all foods are to some degree processed—cooking a food is a form of processing--ultra processed foods contain very few natural ingredients; they are made up primarily of chemicals that are manufactured in factories. Unlike whole foods, they are designed to be transportable, affordable, easy to eat, and have a long shelf life. Because they are human made, they are formulated to be so palatable and satisfying that they are frequently addictive, making it more likely that we’ll eat more, leaving very little room for the fiber that our microbiome needs. Because they are easily digested, frequently melting in our mouths, they spend very little time in our digestive tract, rarely reaching the large intestine where most of the important microbes reside.
People who eat diets high in so-called “junk” foods tend to experience more depressive episodes, anxiety, rumination, and tend to self-isolate. Of course, it is hard to determine which comes first—the junk food or the mood—as we are more likely to eat unhealthy foods when we are in psychological distress. The very nature of ultra processed foods is that they are designed to give us an instant hit of pleasure, just what we crave when we are feeling down, mentally exhausted, or lonely. But eating these foods when we are under stress or struggling emotionally can start a cycle that is hard to break: less fiber results in lower levels of important neurotransmitters that support us while also changing the composition of the gut flora, favoring hostile bacteria, and making it less diverse. This leads to higher levels of inflammation, which further degrades our mental health and keeps us locked in a downward spiral that can be hard to turn around.
Since the start of the pandemic, Americans are reporting more episodes of depression, loneliness, and anxiety as well as higher levels of stress. As we struggle to find the root causes of our collective distress, could it be that one of the culprits lies in what we are feeding our gut? Sometimes the most powerful solutions to chronic problems are hidden in plain sight; few would have thought that planting trees in a chronically crime ridden housing project in Chicago would lead to a stronger community, improved mental health, and safer living conditions. How we care for the creatures that live within us may be a small but important step in taking charge of our emotional well-being. Our microbiome is a reminder that, not only do we seek the lush greenery of nature for restoration and connection, but, as owners of a body that hosts a multitude of species, we also must nurture the organisms that depend on that very same care from us.
I offer you this simple exploration this week: notice what happens to your food choices when you pause to consider how your gut microbes will be impacted by what you eat. Do you eat differently knowing that these critters need fiber to produce important neurotransmitters, fatty acids, vitamins, and minerals that will support enhanced emotional well-being? And if you find yourself eating more ultra processed foods, do you notice a difference in your mood? For those who struggle with gut issues, this may be, unfortunately, a familiar exercise. It is best for all of us to make this an observation, not an exercise in judgment, approached with a broadened awareness with the intention to see what unfolds.