There’s a whole lot of bacteria in your body. To break it all down into specifics, there are 10 times as many bacteria in your body as there are human cells. Beyond that, if you dig even deeper, there’s 100 times the amount of bacterial DNA in your body than human DNA. “You can argue that we’re more bacterial than we are human,” says Ari Grinspan, M.D., an assistant professor of medicine and the director of GI microbial therapeutics at the Icahn School of Medicine at Mount Sinai.
Before you get too grossed out, a lot of this bacteria is super-beneficial. In fact, a good majority of this bacteria that accumulates in your gut—a.k.a. the gut microbiome—is doing work for you. “They are vitally important in digesting some of the food we eat, developing our immune system, and protecting us from harmful bacteria,” says Grinspan. All the more reason to care about the ecosystem of organisms hanging out in your GI tract, so let’s talk specifics.
Bacteria can send signals to our intestines, and vice versa. According to Grinspan, this “crosstalk” can cause your body to make adjustments based on what’s happenin’ in that biome. “Specifically, our immune system may up-regulate or down-regulate certain factors in response to changes in the gut bacteria,” he says. “We are just beginning to understand what this ‘conversation’ is all about, but likely plays a role in promoting health.”
According to Kirsten Tillisch, M.D., chief of integrative medicine at the Ronald Reagan UCLA Medical Center, the microbes in the gut affect whether we develop gut diseases like inflammatory bowel disease or infectious colitis—but also may determine whether or not we will develop other conditions that extend outside the gut. “Obesity, cancer, anxiety, and depression all may be influenced by the type of bacteria living in the gut,” she says. For instance, a Washington University study of twins in which one was lean and the other obese was conducted in 2013. Scientists took gut bacteria from each twin, and introduced it to mice. The mice who received microbes from the lean twin stayed lean, while the mice that received microbes from the obese twin packed on weight.
Since we are constantly ingesting the outside world—food, bacteria, viruses, fungi, parasites—the gathering in your gut is basically an accumulation of your recent experiences. Like an intestinal scrapbook of your daily adventures. “These products interact with the lining of our intestines, which is packed full with immune cells,” says Grinspan. “The immune cells are constantly sampling the contents of our intestine, and they frequently encounter the bacteria that have made a home in our guts.” When the bacteria in your gut changes and you get some new neighbors, your body has to separate friend from foe. “Will we get along with them or will we try to fight them?” says Grinspan.
Every single person has a gut microbiome that is unique to them alone, “sort of like a fingerprint,” says Grinspan. Since we all have general routines—you eat Thai once a week and greens the rest, you’re vegan except on a few special days—scientists are especially interested in changes to the gut bacteria caused by deviations from your personal normal. “Certain exposures can change your microbiome more dramatically than others,” Grinspan says. “Did you eat a salad, or did you eat at that shady restaurant around the corner? Did you just finish a course of antibiotics or travel to India and immerse yourself in a totally different environment?” The vast majority of people will recover back to their “normal” gut microbiome after they return to their “normal” diet and lifestyle, but sometimes they don’t. For instance, a 2015 University of Iowa study linked drug-induced changes to the microbiome to lower metabolism. “This is the new big thing [in research] and absolutely worth exploring,” Grinspan says.
Although the gut microbiome is still a pretty mysterious place, there are some ways you can bolster its health. Focus on probiotics (like in yogurt) and prebiotics—specifically foods that are high in FODMAPS (Fermentable Oligo-, Di-, Monosaccharides and Polyols). “This includes wheat, rye, garlic, artichokes, legumes, milk, honey, apples, pears, watermelon, mango, stone fruits, mushrooms, cauliflower,” says Grinspan. “These foods contain the bacteria our gut loves and thrives on.” Just don’t OD on these, or else you might experiencing gas and bloating—for some people the symptoms can be very uncomfortable. Beyond that, monitor your stress. A study published in the journal Brain, Behavior and Immunity showed that increased stress seems to change the balance of bacteria in your gut, which can throw that microbiome out of whack and compromise your immune function. So it can help to exercise, rest and generally give you body some extra TLC; your gut will thank you!
