Aromatic amino acids that are produced by gut bacteria are necessary for proper brain and nervous system function. You’ve likely heard of the aromatic amino acids tyrosine, phenylalanine, and tryptophan. These are important protein precursors of dopamine, adrenaline, noradrenaline, serotonin, and melatonin neurotransmitters. These chemical messengers regulate sleep, attention, thinking, and multitudes of other critical processes. Too many or too few of these amino acids can have a large impact on our brain and our methylation cycle. You can be certain that individuals who are dealing with depression, fatigue, insomnia, anxiety, worry, panic, and pain have an imbalance in their neurotransmitters. For without optimum levels of neurotransmitters, we cannot experience optimum health, neurological or otherwise.
Although we can get these aromatic amino acids in our diet when we eat protein, the gut microbes also produce these key biomolecules. Yes, bacteria in the gut produce the amino acids we use to make our neurotransmitters, and this is one reason why the gut is often called the “second brain.” This idea is supported by research that shows our gut bacteria produce significant quantities of aromatic amino acids. In a 2010 study, researchers highlighted the fact that bacteria, like plants, have a chemical pathway, called the Shikimate pathway, which allows them to produce tyrosine, phenylalanine, and tryptophan.8 By producing the precursors to the neurotransmitters serotonin, melatonin, dopamine, and adrenaline, our gut contributes a great deal to how we think, feel, and act each day. If the gut bacteria can produce amino acids that turn into neurotransmitters, it is easy to see how our microbiome can impact our brain function.
Giving credence to this idea, researchers have now shown that diverse types of gut bacteria are capable of producing tryptophan, an essential amino acid we simply cannot live without. In a study published in 2014, researchers pointed out that gut bacteria such as Firmicutes, Proteobacteria, and E. coli can produce tryptophan, but this production is altered by use of antibiotics.9 Let that last statement sink in for a moment: research proves antibiotics change how tryptophan is produced in our gut. Tryptophan is an essential amino acid. It is required to produce serotonin and vitamin B3. Our bodies cannot produce tryptophan, so it must come from our diet or our microbiome. Low tryptophan levels lead to a disease called pellagra, which causes diarrhea, dermatitis, dementia, and even death. Without this key amino acid, we will become deficient in vitamin B3 and be unable to produce serotonin.10, 11 Lack of tryptophan will also lead to a loss of NAD, a powerful mitochondrial nutrient linked to muscle wasting, accelerated aging, and even cancer.12, 13 We must keep our tryptophan, B3, and NAD levels optimized, not just for the benefit today, but for the dividends it will pay down the road (you will hear more about this important subject in chapter 10).
Given that nearly everyone reading this book has had at least one round of antibiotics in their lifetime, it would be nice to think that even a single round of antibiotics would cause no harm. And I sincerely wish I could tell you that antibiotics don’t harm brain function, except that the research would disagree. Because depression is associated with low brain serotonin, and antibiotics kill bacteria that produce tryptophan, the logical question to ask would be Do antibiotics actually cause depression?
To solve the riddle of chronic disease and optimum health, we must listen to what the science is trying to tell us. The latest research confirms that antibiotic use will increase the risk of depression. In a massive study published in 2015, which included more than 1 million people, researchers showed that exposure to a single round of antibiotics increases risk of depression by 25 percent, while exposure to more than five rounds increases depression risk by more than 50 percent.14 Now just think about all the hundreds of millions of antibiotic prescriptions used each year in the United States. What are those drugs doing to the long-term mental health of our children, our parents, and our loved ones?
If the latest research on antidepressant use is any indication, the destruction of our gut health is leading to an epidemic of depression. Due in large part to the overuse of antibiotics and destruction of our gut bugs, antidepressant use is skyrocketing! The latest research shows that 10 percent of the US population is currently taking an antidepressant, while roughly 25 percent of middle-aged women in the United States take these drugs every day.15 In other words, a large percentage of American women who should be enjoying the prime of their lives are riddled with anxiety, depression, and other symptoms that make their daily lives a struggle. It seems like we are just trying to put a bandage on a gut-based problem by taking drugs designed to change brain chemistry. Maybe the brain isn’t the problem. Maybe the gut is where we should start!