body’s activities, which in turn impact the expression of our genes. I’ll be going into greater depth about the human microbiome in Chapter 3, but I’ll give you a short primer here because this discussion is important and will be carried throughout the book.
Although we’ve learned to think of bacteria as agents of death for the most part because certain strains can cause lethal infections in compromised hosts, new science is compelling us to consider how some of these microscopic bugs are fundamental to life—and mental health. As you read this, some 100 trillion microbes are colonized in your intestines alone.26 They outnumber your own cells by a factor of about ten, covering your insides and outsides. And they contain estimates of more than 8 million genes of their own, which means that fully 99 percent of the genetic material in your body is not your own. It belongs to your microbial comrades. These microbes not only influence the expression of our DNA, but research reveals that throughout our evolution microbial DNA has become part of our own DNA. In other words, genes from microbes have inserted themselves into our genetic code (mitochondrial DNA being the prime example) to help us evolve and flourish.
A great many of these invisible creatures live within your digestive tract, and while they include fungi, parasites, and viruses, it’s the bacteria that appear to hold the proverbial keys to the kingdom of your biology, as they support every conceivable feature of your health. In the future we’ll likely see how the other microbes contribute at least as much to our health as bacteria do. The microbiome is so crucial to human health that it could be considered an organ in and of itself. In fact, it has been suggested that since without it we could not live, we should consider ourselves a “meta-organism,” inseparable from it. This inner ecology helps you digest food and absorb nutrients, supports the immune system and the body’s detoxification pathways, produces and releases important enzymes and substances that collaborate with your biology (including chemicals for the brain, such as vitamins and neurotransmitters), helps you handle stress through its effects on your endocrine—hormonal—system, and even ensures you get a good night’s sleep. Put simply, your microbiome influences practically everything about your health, including how you feel both emotionally, physically, and mentally.
What compromises a healthy microbiome? Not surprisingly, your microbiome is vulnerable to three antagonizing forces: exposure to substances that kill or otherwise negatively change the composition of the bacterial colonies (these substances include everything from environmental chemicals and drugs like antibiotics to ingredients such as artificial sugars and processed gluten-containing foods); a lack of nutrients that support healthy, diverse tribes of good microbes; and unrelenting stress.
I’ve devoted an entire section to the amazing features of the microbiome, so you’ll gain plenty of knowledge about how it plays a role in your physical and mental well-being and how you can maintain an optimal colony of tribes. We have coevolved with these microorganisms throughout our journey on this planet, and we must respect them for what they are: the body’s—and brain’s—best friend. And they are as much a part of our survival and mental well-being as our own cells are.
DESIGNED FOR DEPRESSION
Have you ever stopped to wonder if depression has benefits? I know, it sounds a little outlandish to even suggest such an idea. But it’s an excellent question to ask and an even better one to answer. This conversation, however, is best couched within the topic of stress in general. So let’s go there next.
Most of us can recognize the symptoms of stress. We feel it inside and out. We become irritable, our heart races, our face may feel hot, we get a familiar headache or upset stomach, our mind is incessantly chattering, there’s a sense of impending doom, and we’re annoyed by the smallest things. For some people, stress has little outward effect. For these individuals, what they feel at the surface is internalized and sometimes expressed as disease. In fact, many of these people don’t believe they experience stress—but they do; they just don’t consciously recognize it until it builds up to a certain point and seeps out in other ways.
The term stress as it is used today was coined by one of the founding fathers of stress research, Hans Selye, who in 1936 defined it as “the non-specific response of the body to any demand for change.”27 Selye proposed that when subjected to persistent stress, both humans and animals could develop certain life-threatening afflictions such as heart attack or stroke that previously were thought to be caused by specific pathogens only. This is a crucial point, because it demonstrates the impact that everyday life and experiences have not only on our emotional well-being but also on our physical health.
The word stress as it relates to emotions became part of our vocabulary in the 1950s. Its use became common with the onset of the Cold War, which was an era when fear ruled. We were frightened of atomic war, so we built bomb shelters. As a society, we could not say we were afraid; instead, we used the word stress. Today we continue to use the word to describe anything that disrupts us emotionally—we’re stressed, stressed out, under stress, and so on. Stress can also be described as the thoughts, feelings, behaviors, and physiological changes that happen when we respond to demands and perceptions. And if those demands placed on us overwhelm our perceived ability to cope, we experience “stress.” In our frenzied minds, we begin to pant silently like an animal and look for an escape.
Since Selye, researchers have broken stress down into several subcategories. Stress physiology has come a long way in the last fifty years in particular, and so have the stressors. A key concept to enter the medical vernacular more recently is what is known as allostatic load. Your allostatic load refers to environmental challenges—the “wear and tear” on the body—that cause it to begin efforts to maintain stability (allostasis, also known as homeostasis). It also represents the physiological consequences of adapting to chronic stress that entails repeated activation of the body’s stress response machinery involving many systems—immune, endocrine, and neuronal. Researchers Bruce McEwen and Eliot Stellar coined this term in 1993 as a more precise alternative to the term stress.28 The key players of the stress response, cortisol and epinephrine (adrenaline), have both protective and adverse effects on the body depending on when and how much they are used. On one hand, these hormones are essential for the body’s ability to adapt and maintain balance (homeostasis), but if they are flowing for a prolonged period or needed relatively frequently, they can accelerate disease processes. The allostatic load, as it’s called, becomes more harmful than helpful. This load can be measured in physiological systems as chemical imbalances in the activities of the nervous, hormonal, and immune systems. It can also be measured by disturbances in the body’s day-night cycle (what’s called the circadian rhythm, another concept we’ll explore later), and in some cases, changes to the brain’s physical structure.
Stress is actually a good thing, at least from an evolutionary and survivalist perspective. It serves an important function: to protect us from real danger by equipping us with a better means to escape a life-threatening situation or face it head on. But our physical reaction doesn’t change according to the type or magnitude of a perceived threat. Whether it’s a truly perilous stressor, or just the to-do list and an argument with a colleague, the body’s stress response is the same. Let me give you a quick lesson on what goes on when your body senses stress so we can come full circle back to, dare I say, the secret value of depression.
First, the brain sends a message to the adrenal glands that results in the release of adrenaline, also called epinephrine. This triggers your heart rate to increase as blood is directed to your muscles in the event you need to flee. When the threat is gone, your body normalizes again. But if the threat doesn’t go away and your stress response intensifies, then a series of events take place along what’s called the HPA axis, short for hypothalamic-pituitary-adrenal axis, and which involves multiple stress hormones. The hypothalamus is a small but key governing region of the brain that has a vital role in controlling many bodily functions, including the release of hormones from the pituitary gland housed inside. It’s often referred to as the seat of our emotions
