If you’ve ever experienced butterflies in your stomach before a speech, you knew the sensation didn’t result from a lost monarch. But this common experience—your gut seeming to act out your brain’s anxiety—is an everyday example of fascinating new research into the interconnected worlds inside us.
While your stomach doesn’t contain butterflies, there are tiny organisms in there that are engaged in a conversation with your brain about that stress you’re experiencing. These organisms and their home could be far more powerful than we’ve realized, according to a burst of new studies. Many of the tens of trillions of organisms in your gut, or gastrointestinal tract, can help maintain good digestion and health. But some of them are not so cooperative: When they take over, they wreak havoc. That might mean you get food poisoning or make more bathroom trips than you’d like—but some might have bigger implications. These nasty bugs could be sending the brain signals connected to brain-related disorders including anxiety and Alzheimer’s disease.
So, is your gut the key to a healthy brain? Here’s what you need to know about the gut-brain connection.
With the help of everyday people, University of California San Diego researchers have uncovered new facets of the worlds within us. As part of the American Gut Project, more than 10,000 people from around the world mailed in their poop (yep). Scientists analyzed it to understand how organisms inside us—our microbiomes—interact with diet, lifestyle, and disease.
Learn more about the powerful gut-brain connection in a free webinar on June 9, moderated by Joan Lunden and hosted by Prevention, HealthyWomen, and the Women’s Alzheimer’s Movement at Cleveland Clinic.
You may remember the word “biome” from biology class—a habitat such as desert or grassland, designated based on local climate and plant life. Our bodies contain their own worlds, unique habitats of trillions of wee beasties—viruses, fungi, bacteria, and other microorganisms living on us and inside us. In humans, microbes gather in these worlds on the skin, in the nose, and in the gastrointestinal tract (a.k.a. the gut). Over the past 20 years, experts have refined techniques to “fingerprint” the gut’s cast of microbes through sequencing DNA, says Ami Bhatt, M.D., Ph.D., an associate professor of medicine and genetics at Stanford University.
You’ve had a microbiome since the day you were born, and it’s been evolving and growing with you. On your ride through the birth canal, your gut filled with a wide cast of microorganisms passed along by your mom. Then skin-to-skin contact, first foods, infections (and antibiotics), and all those germy toys changed your microbiome. Each new interaction, from childhood on, brings in guest stars, removes old standbys, and casts long-term recurring roles—your gut’s world is constantly in flux.
Animal and human research has found that the gut microbiome can be influenced by environmental factors such as chronic stress, artificial sweeteners, pesticides, disinfection, and ultrafine particles in polluted air. You can pick up new gut bacteria from your pet or a bad meal, Dr. Bhatt notes. Ultimately, microbial worlds wholly unique to you inhabit your body.
Helpful gut microorganisms have processes for breaking down foods and turning them into ingredients our bodies use. They develop the immune system, block pathogens, synthesize vitamins, and more.
In the past, you’ve probably lost your appetite because of stress or sadness—or falling in love. Maybe you’ve “followed your gut” or made a “gut decision.” These familiar terms and experiences clue us in to why some researchers are now calling the gut our “second brain” and saying bacteria may be the “master puppeteers” of our brains.
Scientists aren’t sure yet how the gut’s microbiome influences the brain—but it seems to be a fascinating two-way relationship. For example, among middle-aged adults, a more diverse microbiome was associated with better performance on cognitive tests. Various theories posit that the gut produces molecules that signal the brain via the bloodstream or the enteric nervous system. For example, specific gut bacteria can detect and increase the production of serotonin, which is associated with feelings of contentment. In fact, 90% of the . Another kind of bacteria commonly found in the human gut, Lactobacillus rhamnosus, actually contains a neurotransmitter that can help calm anxiety. Other bacteria may influence our social behavior and interactions and our responses to stress.
“It’s a two-way street of feedback loops” between the gut and the brain, says researcher Laura Cox, Ph.D., a Harvard assistant professor seeking to understand how the microbiome can affect the brain in aging.
Sometimes unhelpful critters stage a takeover of the gut. This overpopulation can lead to gut dysbiosis, a negative imbalance that seems to cause static in the body’s communication lines and influence the brain’s everyday work. For example, gut dysbiosis is associated with depressive-like behaviors. In an animal study, transferring a mood-disordered animal’s gut bacteria into a healthy animal led to depressive symptoms for the formerly well animal, says Smita Patel, D.O., a neurologist and sleep specialist at iNeuro Institute. Other research is investigating the links between the gut microbiome and ADHD, autism spectrum disorders, anxiety, and stress.
Unhelpful gut microbes may create irritants to the immune system that travel through the bloodstream and influence the brain’s immune cells. For example, the guts of compared with those of similar adults and are often overpopulated with a specific microbe. This microbe may impair immune functions related to clearing a plaque built upon the brain’s structures that is related to Alzheimer’s symptoms. Sex-based differences come into play as well, says Cox. The gut microbiota can regulate levels of hormones, including estrogen. When gut dysbiosis sets in, estrogen levels can change, possibly influencing cognitive decline.
Fascinating research is now being done by the Alzheimer Gut Microbiome Project in collaboration with 10 Alzheimer’s Disease Research Centers and three major diet and lifestyle modification clinical trials. At-home fecal and blood collection kits from more than 3,000 racially diverse participants are being analyzed to help researchers understand gut microbiome changes across the stages of Alzheimer’s disease. The project is also exploring lifestyle and diet impacts on Alzheimer’s disease–related cognitive outcomes and gathering new evidence on the gut-brain axis of communication.
If researchers can home in on the precise mechanisms and environmental factors that make these connections work, they may be able to slow or prevent the Alzheimer’s processes that begin in people’s 50s or even earlier. The gut houses a world of information, and we are learning from it every day.
Your microbiome is potentially modifiable, Dr. Patel says. Tweaking your microbiome could help prevent or treat brain-related diseases or mental health conditions.
“The lowest-hanging fruit for intervention is diet,” Dr. Patel says. “A diet rich in plants, unsaturated fats, and vegetable oils and low in refined sugars and red and processed meat has been shown to increase gut microbe diversity and reduce physiological changes such as chronic inflammation.”
For example, according to the UC–San Diego study, those who ate more than 30 unique plant foods per week had more diverse gut micro biomes than those who consumed 10 or fewer types weekly. While eating 30 different plant foods every week might seem like a gutsy ask, any improvement helps. The average American consumes only 0.9 cups of fruit and 1.4 cups of vegetables per day, far below recommended amounts. A quick refresher: Plant foods are anything but meat and animal products and include fruits, vegetables, whole grains, legumes, nuts, seeds, herbs, and spices. A multigrain sandwich with hummus (fiber-rich garbanzo beans, olive oil, and seed-based tahini), tomatoes, avocado, lettuce, sprouts, and red peppers could supply at least 10 plant foods in just one meal. Chart your plant foods for a week—you may find yourself trying new foods or ones you’ve forgotten about.
The fiber in your lunch’s veggies, grains, and beans can increase bacterial colonies and species diversity. When gut microbes are fed complex carbs, they ferment the fiber-rich food, producing helpful metabolites that promote gut health. In essence, Cox says, fiber can help feed good microbes and promote a healthy microbiome. High amounts of fiber are found in beans, whole-grain cereals, broccoli, cauliflower, and even raspberries. (But switching too quickly to a high- fiber diet can lead to uncomfortable gas, Cox says.) If you add sauerkraut, tempeh, or fermented tofu to your sandwich, you may get extra gut points. Fermented foods can help “seed” good microbes, Cox says.
There’s one wise takeaway experts agree on: “Be thoughtful about your food choices,” Dr. Bhatt says. “You’re eating for trillions.”
Studies suggest that stress, sleep rhythm disturbances, and lack of exercise are linked to an imbalanced gut microbiome. Increasing your exercise, relaxation, and sleep can create a more diverse gut microbiome, Dr. Patel says. Exercise’s blood flow kickstarts the gut’s and nervous system’s activity, contributing to a healthier gut, Cox adds. Aerobic exercise has been shown to increase gut microbiome diversity and abundance.
Reduce stress by trying meditation or yoga, Dr. Patel suggests, and get the recommended seven to nine hours of sleep at night. Focus for a week on getting enough water (which helps move food through the intestines) and taking a 30-minute walk during lunch or after work, she says. “A healthy lifestyle isn’t an overnight accomplishment,” she adds. “It’s an accumulation of daily practices resulting from making conscious decisions.”
Antibiotics can be lifesaving, but it is important to avoid unnecessary exposure to them to minimize “collateral damage” when good bacteria die off alongside bad bacteria, Dr. Bhatt says.
Probiotic supplements can help boost beneficial bacteria after you’ve taken a round of antibiotics or if you’ve endured a bacterial bug. But microbes you consume don’t stick around after you cease your daily dose, Cox says. Some probiotic supplements may help some people but make others feel worse; it depends on a person’s level of immune system inflammation and unique genetic makeup, she says, adding that the FDA doesn’t regulate most probiotics found in yogurt and other over-the-counter products. “Before you pay for a probiotic, see what it does,” she suggests—this may require reading the manufacturer’s studies or other health research. Be skeptical of sweeping claims regarding the gut microbiome, Dr. Bhatt says. “These are early days, and we’re working to understand this very complicated web of interactions, though there’s a ton of promise. As in the rest of life, there aren’t simple answers.”
People struggling with anxiety and depression can experience digestive symptoms such as gas and bloating. “Often these cognitive and digestive symptoms are thought to be independent of one another, ignoring the important link between the gut and the brain,” says Smita Patel, D.O. Watch for symptoms like these, and try dietary and lifestyle solutions. If those don’t help, talk to your doctor.