Your brain’s health is dictated by what goes on in your gut. That’s right: What’s taking place in your intestines affects not only your brain’s daily functions, but also determines your risk for a number of neurological conditions in the future.
Your intestinal organisms, or microbiome, participate in a wide variety of bodily systems, including immunity, detoxification, inflammation, neurotransmitter and vitamin production, nutrient absorption, whether you feel hungry or full, and how you utilize carbohydrates and fat. All of these processes factor into whether you experience chronic health problems like allergies, asthma, ADHD, cancer, type 2 diabetes, or dementia.
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 (see “How Diet Can Make — or Break — Your Mental Health“).
Put simply, nearly everything about our health — how we feel both physically and emotionally — 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.
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.
5 Ways to Boost Your Brain Through Your Gut
I am frequently asked how long it takes to rehabilitate a dysfunctional or underperforming microbiome.
Research shows that significant changes in the array of gut bacteria can take place in as little as six days after instituting a new dietary protocol, like the one I present in my book (the highlights of which I’m sharing here). But everyone is different; your Brain Maker rehab will depend on the current state of your gut and how quickly you commit to making changes.
1. Eat Foods Rich in Probiotics
Probiotics are live bacteria and yeast that support good digestive health. Long before probiotics became available in supplement form, the health benefits of fermented, probiotic-rich foods like kimchi, sauerkraut, and yogurt were well recognized. The Chinese were fermenting cabbage 6,000 years ago.
The type of fermentation that makes most foods rich in beneficial bacteria is called lactic-acid fermentation. In this process, good bacteria convert sugar molecules in food into lactic acid, and, in doing so, the good bacteria multiply. This lactic acid, in turn, protects the fermented food from being invaded by pathogenic-bacteria because it creates an environment with a low pH. This kills off harmful bacteria, which has a higher pH.
While supplements are helpful, there’s still no better way to consume bifidobacteria and lactobacilli (some of the most important healthy bacteria in the gut) than to get them from food sources, which are easiest for the body to use.
These probiotic bacteria help maintain the integrity of the gut lining; serve as natural antibiotics, antivirals, and antifungals; regulate immunity; and control inflammation. They even improve nutrient absorption.
These are some of the best food sources for probiotics (for more ideas, visit “Probiotics at Work“):
- Live-Culture Yogurt: Check the label to make sure your yogurt contains live cultures, and avoid products that are heavily sweetened. Coconut yogurt is an excellent alternative for people who are sensitive to dairy.
- Kefir: A fermented-milk product that has a more liquid texture than yogurt.
- Kombucha Tea: A tart, fizzy, fermented black tea. (Enjoy this DIY kombucha recipe.)
- Kimchi: Spicy, fermented vegetables that are Korean in origin. Kimchi is one of the best probiotic foods you can add to your diet.
- Sauerkraut: Real, fermented sauerkraut (instead of cabbage soaked in vinegar) fuels healthy gut bacteria and contains choline, a chemical needed for proper transmission of nerve impulses from the brain through the nervous system. You can make your own real sauerkraut at home or find it in the refrigerated section of grocery stores.
- Pickles: The most basic and beloved probiotic. As with sauerkraut, choose real, brined pickles that have been refrigerated.
2. Go Lower-Carb; Embrace High-Quality Fats
A diet that keeps your blood sugar balanced keeps your gut bacteria balanced. A diet high in rich sources of fiber from whole vegetables and fruits feeds good gut bacteria and produces the right balance of short-chain fatty acids to keep the intestinal lining in check. A diet that’s intrinsically anti-inflammatory is good for the brain.
Diets high in sugar and low in fiber fuel unwanted bacteria and increase the chances of intestinal permeability, mitochondrial damage, a compromised immune system, and widespread inflammation that can reach the brain. It’s a vicious cycle; all of these further disrupt our protective microbial balance.
We’ve been taught to demonize saturated fat. But coronary artery disease — a leading cause of heart attacks — may have more to do with inflammation than high cholesterol. And a great deal of research shows that when cholesterol levels are low, the brain simply doesn’t work well.
Studies of deceased patients with Alzheimer’s found significantly reduced amounts of fats in their cerebrospinal fluid compared with controls. People with low cholesterol are at much greater risk for neurological problems, including depression and dementia.
I have a host of recipes in my book, but here’s the cheat sheet: Make your main entrée mostly fibrous vegetables and fruits that grow above ground, with protein as a side dish. Far too often people think that a low-carb diet is all about eating copious amounts of meat. Much to the contrary, an ideal plate in the Brain Maker protocol is a sizeable portion of vegetables (two-thirds of your plate) and about 3 to 4 ounces of protein. You’ll get your fats from those naturally found in the protein, from butter and olive oil used to prepare the dish, and from nuts and seeds.
3. Enjoy Chocolate, Coffee, Wine, and Tea
You can rejoice in the fact that, as far as your brain’s health is concerned, you can embrace chocolate, coffee, and wine in moderation, and tea to your heart’s desire.
Research abounds concerning dark chocolate’s benefits. In one study, Italian researchers demonstrated that in elderly individuals suffering mild cognitive impairment, those who consumed the highest level of flavonols (one category of polyphenols) from cocoa and chocolate showed heightened cognitive function.
Other studies have shown that consuming flavonols leads to improved blood flow to the brain, which is typically diminished in dementia patients.
Like chocolate, coffee supports a healthy balance of gut flora and exhibits anti-inflammatory and antioxidant properties. Coffee and chocolate also stimulate a specific gene pathway called the Nrf2 pathway. When triggered, it causes the body to make higher levels of protective antioxidants, while reducing inflammation and enhancing detoxification. Other Nrf2 activators are green tea, turmeric, and resveratrol, a compound in red wine.
On that note, Spanish researchers have found that LPS levels, a marker for both inflammation and intestinal permeability, were dramatically reduced in individuals who consumed red wine in moderation (one to two glasses per day).
Polyphenols found in black tea are now being explored for their ability to positively influence gut microbial diversity. They’ve been shown to increase bifidobacteria, which help stabilize gut permeability. Green tea has also been shown to increase bifidobacteria and to lower levels of potentially harmful bacteria species.
4. Consume Foods Rich in Prebiotics
Prebiotics are food-borne fuel for the beneficial bacteria that live in the gut, and they occur naturally in raw garlic, cooked and raw onions, leeks, chicory, Jerusalem artichokes, and jicama. Estimates suggest that for every 100 grams of prebiotic carbohydrates we consume, a full 30 grams of good gut bacteria are produced.
Prebiotics have many additional benefits, including the ability to reduce inflammation in inflammatory-bowel disorders, enhance mineral absorption, and promote a sense of satiety. Animals given prebiotics produce less ghrelin, the hormone that signals the brain that it’s time to eat.
5. Drink Filtered Water
Consuming plenty of water is important to intestinal health, but it’s critical that the water doesn’t contain gut-busting chemicals like chlorine. Environmental toxins can disrupt the microbiome and disturb brain physiology.
I recommend using a household water filter. There are a variety of home water-treatment technologies available, from simple filtration pitchers to under-sink units with a separate spigot. Make sure the filter you buy removes chlorine as well as other contaminants, and be sure to maintain and change it regularly.
Finally, ditch plastic water bottles and choose reusable bottles made from stainless steel or glass instead.
From Brain Maker by David Perlmutter, MD. Copyright © 2015 by David Perlmutter, MD. Reprinted by permission of Little, Brown and Company, New York, NY. All rights reserved.