Your gut can make or break your health. Investing in your body's good bacteria may help you avoid illness, dodge upset stomachs, and have more energy.
Credit: Illustration: Sarah Wilkins

If it seems like every time you walk in to the pharmacy or supermarket, the number of products trumpeting "probiotic" qualities has multiplied, you can blame your microbiome. The microbiome is the collective term for the trillions of microbes that live on your skin, in your nose and mouth, on your genitals, and, most notably, in your gut. All told, the bacteria that live in you and on you account for about five pounds of your body weight. And that's where probiotics come in: These are products that claim to contain healthy bacteria, essentially to add to your own microbiome. There's growing consumer interest in probiotics because researchers are discovering that the bacterial ecosystem exists in a delicate balance with the health of the human that hosts it. In the last decade, studies have shown that the composition of our microbiome is correlated with a wide range of health outcomes—the healthier the bacteria, the healthier the human. Our bacteria, ourselves.

Dr. Maria Marco is a microbiologist and a professor of food science and technology at the University of California, Davis. She studies bacteria, particularly lactic acid bacteria, in food and in our bodies. Lactic acid bacteria are what ferment milk into yogurt, cabbage into sauerkraut, and what give sourdough that lovely tang. They also live in our intestine.

"Having a larger number of lactic acid bacteria in our intestine has been associated with good health for many years," she says. "When you look at microbes in the intestines, there are patterns. You see different species depending on the health status of the individual. There are correlations. We can say: These are the different species of bacteria that are there. And we have been able to associate these different bacteria with problems like obesity, autism, dermatitis. What we need to do now is establish causation."

In other words, scientists have established that people who have a thriving colony of good bacteria in their gut are often healthier in lots of ways than people who don't. When you look at the colony of bacteria in someone's intestine, you can associate certain kinds of bacteria with certain health factors in that individual, both good and bad. But scientists don't really know why and how the bacteria are affecting us this way.

"Understanding how the bacteria work is at the nexis right now," Dr. Marco says. "We have to study how the bacteria are working at a molecular level, to really start to understand how this is happening."

Although the science is still evolving, researchers hypothesize that disruptions to our microbiome could account for the rise in obesity, diabetes, and allergies, and a whole host of other problems, like colitis, heart disease, eczema and even some cancers.

Dr. Daniel M. Neides, Vice Chair of the Wellness Institute at the Cleveland Clinic, says that the role bacteria play in our health appears to be linked to the immune system and the inflammatory response that happens when the immune system is activated.

"The bacteria act as defense. If you disrupt the microbiome on your skin, you're at risk for infection. In the gut, you can have digestive problems," he explains. "But it's not only defense. The bacteria work in concert with the immune system itself, keeping the inflammation at low levels. When the immune system is quiet, we are healthy. When there's systemic inflammation, problems occur."

Dr. Marco envisions a future in which scientists have established that certain species of bacteria are good for certain ailments. So if you have high blood pressure or colitis, or even depression, you may need an infusion of a particular strain of bacteria. We're certainly not there yet, but Dr. Marco says that as researchers establish causality between the presence or absence of certain bacteria and specific health outcomes, mapping an individual's gut microbiome could become a crucial piece of information used to treat disease.

In the last 100 to 150 years, there have been myriad medical and food system advances, but some of those advances have come with a cost to our bacteria. Most people in developed countries are simply not exposed to the wide range of bacteria that we would have been a century ago. Factors that have limited our exposure to microbes include the advent of refrigeration, pasteurization of milk, highly processed, sugary foods, antibiotics, c-sections, antibacterial soap and gels, and less gardening or farming. Nobody is suggesting that you shouldn't take an antibiotic when you need it—but you should perhaps also recognize the antibiotic's cost to your microbiome and take steps to mitigate that cost.

Exactly how to do that is little more complicated than snapping up every product that claims to be probiotic, or choosing sourdough for your peanut butter and jelly. Click here to get science-based pointers on the care and feeding of your microbiome.