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The Gut, Microbiome, and Brain: A Powerful Triangle
Some of the most exciting research from the past few years shows remarkable connections between the gut, microbiome, and brain. The microscopic creatures living in our intestinal lining produce a number of biochemical reactions that have a profound effect on both our brain chemistry and on the brain cells themselves.
An imbalanced microbiome activates the immune system, which is adjacent to the microbiome in the gut wall. Microbial imbalance also frequently erodes the gut wall and leads to poor gut function. The whole process results in intestinal permeability—aka leaky gut—a process by which partially digested food leaks through the gut wall and into the bloodstream. The immune system doesn't recognize food in this form, so it goes on alert, which creates a constant, low-grade immune response. This is known as chronic inflammation, and it can lead to a number of chronic diseases, including obesity, diabetes, heart disease, autoimmune conditions, and cancer.
Meanwhile, the excessive immune reaction also affects the brain via the microglia—specialized immune cells found in the brain. In a healthy condition, the microglia seek out damaged neurons and infections and clear them from the brain.
But when the microbiome is imbalanced, the microglia produce cytokines, inflammatory messengers that can seriously damage the brain. As a result, brain function is altered. Anxiety, depression, and brain fog are the result.
You can significantly turn this situation around with the use of probiotics—pills, powders, or capsules that contain billions of healthy bacteria. Probiotics help restore balance in your microbiome, while reducing inflammation throughout your body and brain; they are a significant part of my treatment of depressed, anxious, or “foggy” patients. New research shows that probiotics raise your brain's level of IL-10, an anti-inflammatory cytokine that helps fight off the inflammatory type in order to protect and support your brain.
Another supplement that fights depression is butyrate, a type of acid produced in the gut. A 2013 article in Behavioral Pharmacology found that butyrate can be very helpful in medicating depression—I've prescribed butyrate for many of my patients, while simultaneously working to rebalance their microbiome so that, eventually, the healthy and restored microbiome could produce its own butyrate.
In a 2013 placebo-controlled, double-blind study published in the journal Gastroenterology, researchers observed the effect of probiotics on brain function. They gave the female participants a fermented milk drink three times a day; some women were given the drink plain, whereas others had drinks supplemented with extra probiotics. When the women's brains were examined via MRI, the probiotic group showed changes in the midbrain region—the area involved in emotional processing.
Similar research was published in 2007 in the European Journal of Clinical Nutrition. In that study—also placebocontrolled and double-blind—subjects who were given fermented milk with extra probiotics reported significantly improved mood compared with the people who had just been given the milk. I've seen these results in my own patients, who indicate that probiotics and other microbiome supports make them feel better with surprising speed.
Bacteria and Brain Chemistry
The microbiome does affect the brain—but our biochemistry is so complex that we are only just beginning to discover some of the many types of gut-brain interaction. The microbiome can alleviate depression and anxiety in four key ways: Healthy bacteria produce key neurotransmitters, the biochemicals that express mood. Serotonin, which creates a sense of optimism, confidence, and well-being, is produced by gut bacteria. So is gammaaminobutyric acid (GABA), which creates a soothing sense of calm.
Bacteria produce a number of biochemicals that improve brain function, mood, and mental vitality.
Microbes send messages to the endocrine system, supporting the HPA axis (hypothalamus, pituitary, and adrenals). This, in turn, modulates the body’s production of cortisol and stress hormones, which prevents anxiety and depression.
A healthy microbiome triggers the immune system to send messages to the brain, instructing it to decrease anxiety and depression.
Individual studies reveal the powerful connection between mood and microbiome. In 2007, for example, Nature published an article about Lactobacillus acidophilus, a type of bacteria found in yogurt, kefir (fermented milk), and many other fermented foods. This common microbe stimulates the brain's opioid and cannabinoid receptors—the very same receptors that are stimulated by opiates (painkillers, heroin, and other drugs) and cannabis. So the next time you want a natural high, reach for the yogurt—or better yet, the sauerkraut!