What you might not know is that your microbiome also affects your mood, your libido, and even your perceptions of the world and the clarity of your thoughts. A dysfunctional microbiome could be at the root of your headaches, anxiety, inability to concentrate, or even negative outlook on life.
Put simply, nearly everything about our health — how we feel both physically andemotionally — can hinge on the state of our microbiome. In fact, the connection between gut flora and the brain is so important that in 2014 the National Institute of Mental Health spent more than $1 million on a research program to study this relationship.
In my work as a neurologist, I’ve discovered that no other system in the body is more sensitive to changes in gut bacteria than the central nervous system. What’s more — and this is the good news — I have seen dramatic turnarounds in brain-related conditions with simple dietary modifications and, on occasion, with more-aggressive techniques to reestablish a healthy microbiome.
If you’re wondering how to care for your own microbiome in a way that can change your brain for the better, check out my new book, Brain Maker. Here are some of the details of that program.
Meet Your Second Brain
Understanding just how closely the gut and the brain are related is essential.
Think of the last time you felt sick to your stomach because you were anxious, scared, or over-the-moon elated. Scientists are learning that this intimate relationship between the gut and the brain is bidirectional: Just as your brain can send butterflies to your stomach, your gut can relay its state of calm or alarm to the brain.
The vagus nerve, the longest of 12 cranial nerves, is the primary channel between millions of nerve cells in our intestinal nervous system (sometimes called the enteric nervous system) and our central nervous system, which comprises the brain and spinal cord. “Vagus” is Latin for “wanderer,” an apt name for this nerve that runs outside the brain and through the digestive system. The vagus extends from the brain stem to the abdomen, directing many bodily processes that don’t require thought, like heart rate and digestion.
At the same time, the bacteria in the gut directly affect the function of the cells along the vagus nerve. And some of the gut’s nerve cells and microbes release neurotransmitters that speak to the brain in its own language.
The neurons in the gut are so innumerable that many scientists are now calling them the “second brain.” This second brain not only regulates muscle function, immune cells, and hormones, but also manufactures an estimated 80 to 90 percent of serotonin (the “feel-good” neurotransmitter).
This means the gut’s brain makes more serotonin — the master happiness molecule — than the brain in your head. Many neurologists and psychiatrists are now realizing that this may be one reason antidepressants are often less effective in treating depression than proper dietary changes.
There are other chemicals manufactured in the gut that are also critical for the nervous system. GABA is an amino acid produced by gut bacteria that calms nerve activity by inhibiting transmissions and normalizing brain waves, helping return the nervous system to a steadier state after it’s been excited by stress.
Glutamate, a neurotransmitter also produced by gut bacteria, is involved in cognition, learning, and memory. It is abundant in a healthy brain. A slew of neurological challenges — including anxiety, behavioral issues, depression, and Alzheimer’s — have been attributed to a lack of GABA and glutamate.
Leaky Gut, Leaky Brain
You may have heard about the perils of a leaky gut, where the protective junctions in the intestinal lining become compromised. This is a response to a variety of factors, including pathogenic bacteria, some medications, stress, environmental toxins, elevated blood sugar, and potentially gut-irritating food ingredients like gluten.
Once the intestinal barrier is compromised, undigested food particles leak into the bloodstream, where they elicit an immune response. This can create systemwide inflammation.
When your intestinal barrier is compromised, you become susceptible — due to that increased inflammation — to a spectrum of health challenges, including arthritis, eczema, allergies, and even autism, Alzheimer’s, and Parkinson’s. (For more on leaky gut syndrome, see “How to Heal a Leaky Gut“.)
Still, the problems of a leaky gut become even more monumental in light of new science that shows how loss of gut integrity can lead to a “leaky” brain.
We’ve long assumed that somehow the brain was insulated from what goes on in the rest of the body. You’ve heard about the highly protective, fortified portal keeping bad things out of the brain — the blood-brain barrier. We used to think of this barrier as an impenetrable wall.
It has now become clear that many substances threaten its integrity. And once the brain’s barrier is compromised, various molecules that may spell trouble — including proteins, viruses, and bacteria — can get inside it.
For an example of how dangerous this can be, look at how the lipopolysaccharide (LPS) molecule behaves once it gets outside the gut.
LPS makes up the protective outer membrane of a class of bacteria that typically represents 50 to 70 percent of our intestinal flora. We’ve long known that LPS induces a violent inflammatory response in animals if it finds its way into the bloodstream. It’s so violent that it’s also termed an endotoxin, a toxin that comes from within the bacterial cell.
In one critically important study on LPS, researchers at Texas Christian University showed that injections of LPS into lab animals’ bodies (not brains) led to overwhelming learning deficits, demonstrating that LPS was able to cross the blood-brain barrier.
In addition, the animals developed elevated levels of the protein beta-amyloid in their hippocampi, the brain’s memory center. (Beta-amyloid is strongly implicated in Alzheimer’s.)
Other studies have implicated LPS in memory problems and decreased production of BDNF (brain-derived neurotrophic factor), a protein that is critical for the growth of new brain cells.
This is powerful information that once again speaks to the gut-brain connection and the impact of inflammation, gut permeability, and the critical importance of a healthy gut to a healthy brain.
Food Matters
Perhaps the most significant factor related to the health of the microbiome — and thus, the brain — is the food we eat. It is also the greatest challenge to the microbiome and brain. Food matters enormously, trumping other factors in our lives that we may not be entirely able to control.
As I described in my previous book, Grain Brain, the two key mechanisms that lead to brain degeneration are chronic inflammation and the action of free radicals, which are byproducts of inflammation that cause the body to “rust.” (For an excerpt from Grain Brain, see “Overcoming Grain Brain“.)
Brain Maker takes a new look at these mechanisms to understand how they are influenced by gut bacteria and overall gut health. My recommendations are designed to treat and prevent brain disorders; alleviate moodiness, anxiety, and depression; bolster the immune system and reduce autoimmunity; and improve metabolic disorders, including type 2 diabetes and obesity, which factor into long-term brain health.
The idea that food is the most important variable in human health is not news. But our new understanding of the connection between what you eat and how it affects your microbiome, and your brain, is exciting.
You can change the state of your microbiome — and the fate of your health — through dietary changes, opening the door for better health in general, and improved brain function in particular. My plan, outlined on the following pages, can help you get started.