Deep in your digestive system, 39 trillion “bugs” are hard at work 'round the clock keeping you healthy. “You have a rainforest inside you,” says Jack Gilbert, a University of California San Diego professor and microbiome researcher. “It’s incredibly complicated and incredibly connected.”
It’s true. Your gut microbiome has important body-wide effects. The complex community of bacteria and other critters in your intestines break down food and churn out chemicals that keep your bowels regular, tune up immunity, help regulate body weight, blood sugar and blood fats, tamp down inflammation, influence your moods and may even play roles in thinking and memory, according to recent research. A diverse gut microbiome has been linked with a longer, healthier life in a headline-grabbing 2021 study of 4,560 adults ages 18 to 98 from the Institute for Systems Biology in Seattle.
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No wonder taking care of gut health has become a national obsession. Sales of probiotic supplements that promise to deliver good bacteria to your gut topped $800 million in 2020, while sales of “prebiotics” — indigestible fibers that gut bugs thrive on — have doubled every year since 2016. Probiotics and prebiotics are turning up in gut-friendly fortified chocolate, snack bars, soda, oatmeal, peanut butter, dried fruit and breakfast cereal. Intestinal “cleanses,” special diets and at-home microbiome stool tests promise to bolster gut wellness, too.
But most of the time, you don’t need these pricey products to promote gut health, says microbiome researcher Joseph Murray, M.D., a gastroenterologist at the Mayo Clinic in Rochester, Minnesota. “Eat real food,” he says. “Probiotics are probably pretty safe, but very few studies show robust benefits.” What new science does show is that your inner zoo loves the simple life — healthy foods and smart habits proven in recent studies to support a diverse gut microbiome and the real-world benefits of a healthy gut.
Happy microbiome, healthy you
Your microbiome can’t be seen, but sometimes it can be heard. You’ve likely had to stifle the excess gas they burp out when chomping on fiber from that bean burrito you had for lunch, for instance. But beneficial gut bacteria churn out other compounds with big benefits including:
- Short chain fatty acids (SCFAs), which can slip into the bloodstream and travel to the liver and to tissues throughout the body, playing roles in appetite, feelings of satisfaction after eating, blood sugar absorption and how the body uses cholesterol. Other SCFAs stay in your intestines, where they can help kill off colon-cancer cells and help lower inflammation in the gut.
- Indolepropionic acid, which mops up cell-damaging compounds called free radicals and may lower risk for type 2 diabetes.
- Neurotransmitters like serotonin and GABA (gamma aminobutyric acid), which may explain links between the microbiome and depression. It’s not just your brain that produces these feel-good chemicals, Gilbert says. “A healthy gut microbiome will have a lot of bacteria that produce GABA, which in the intestines helps the gut nervous system regulate gut peristalsis, where the gut contracts and pushes food down the intestines. That helps keep you regular,” he says. But GABA also controls the way brain cells communicate. It may not be a coincidence that gut-health problems like constipation and diarrhea often come along with depression, he says.
Overall, a diverse microbiome is a good thing, says Hannah Wastyk, a former Stanford University gut-bug researcher now studying the microbiome’s potential to treat inflammatory disease. “A healthy microbiome has 250 to 300 different species of bacteria,” she says. “Low would be 70 to 80 species.” In people, low diversity has been associated with inflammatory bowel disease, psoriatic arthritis, type 1 and 2 diabetes, obesity and arterial stiffness. Diversity means a wider variety of beneficial bugs — including backups if something happens to one type, Murray says. “Each of us has a unique microbiome,” he says. “Some is from what we eat, some of it is from our mother, some is genetics, some is the result of bad things we do to it, such as antibiotics that may kill bacteria that are our friends in that community.”
Gut health hacks that work
You can nurture a diverse gut microbiome for good gut health without supplements, fortified foods or microbiome tests. Experts say these six everyday strategies work:
1. Eat fermented foods regularly
People who had fermented foods — like yogurt, sauerkraut, kimchi, the yogurt-like drink kefir or kombucha (a fermented beverage) — daily for 10 weeks increased the diversity of their gut microbiome in an August 2021 Stanford University study. But study participants who ate more high-fiber foods saw no increase in diversity, a finding that shocked the researchers, according to Wastyk, colead author of the study. “No one expected the fermented foods group to have that response,” she says. “Everyone was like, 'What the heck?'”
Even more surprising: Just 10 percent of the good bacteria found in the fermented foods actually took up residence in participants’ gut. Wastyk thinks fermented foods may increase diversity by knocking the microbiome a little off-balance, giving small colonies of existing bacteria a chance to grow. Wastyk suggests finding several fermented foods you enjoy and having some daily. Look for yogurt with live, active cultures and for foods that haven’t been heat-processed, which would kill off the bacteria, she adds.
2. Eat a wider variety of produce
When over 10,000 people mailed stool samples and diet data to the American Gut Project started by Gilbert at the University of California San Diego, researchers found that those who munched 30 or more types of produce in a week had a more diverse gut microbiome than those who had fewer than 10 types. Doing this was more important for gut-bug diversity than whether participants were vegetarians or meat eaters. Having an assortment of fruit and veggies delivers a wider variety of types of fiber, starches and other nutrients that feed a wider variety of bacteria, Gilbert explains. “Don’t just eat peas for dinner,” Gilbert says. “Eat the rainbow. The colors [of fruit and vegetables] are chemicals that feed different types of bacteria.”
Include broccoli, cabbage and cauliflower. Brassica-family veggies like these (and also collard greens, bok choy, arugula and Brussels sprouts) feed beneficial bacteria that suppress gut bugs linked to ulcerative colitis and irritable bowel syndrome. Bacteria that eat brassicas also teach the gut immune system to produce the cushy, protective mucus that lines the inner wall of the intestines, Murray explains. But that’s not all. Microbes in the gut convert glucosinolates in brassica veggies into active isothiocyanates that help prevent cancer.
3. Toast your good bugs with a mug of tea or coffee
Plant compounds called polyphenols found in coffee and black or green tea can increase the number of beneficial bacteria that protect the inner lining of the intestines and that pump out short-chain fatty acids. Gut bugs also convert polyphenols into forms that have protective effects in the body, including preventing inflammation, protecting cells from damage and even guarding against cancer. Your microbiome will also love polyphenol-rich berries, asparagus, artichokes and olives.
4. Go fish
People who ate five salmon or cod dinners per week for eight weeks saw levels of a group of undesirable gut bugs called Bacteroidetes drop, compared to people who skipped fish and had their usual dinners in a 2021 study from Norway. Bacteroidetes are associated with type 2 diabetes, the researchers note. In other studies, people with higher blood levels of good fats had greater microbiome diversity and more beneficial bacteria even if they weren’t eating a high-fiber diet.
5. Cut back on artificial sweeteners and emulsifiers
Sucralose, aspartame and saccharin can mess with microbiome diversity in ways that may interfere with the body’s ability to absorb blood sugar, Canadian researchers say. “And strong emulsifiers in processed foods can break up the protective layer of mucus in the intestines where there are lots of good bugs cavorting around,” Murray says. In a 2021 study, French researchers found that the emulsifiers carboxymethylcellulose and polysorbate 80 “profoundly impact intestinal microbiota in a manner that promotes gut inflammation and associated disease states.”
6. Skip probiotics most of the time
The certainty of scientific evidence is low that probiotic supplements can help adults avoid diarrhea while taking antibiotics, treat ulcerative colitis or Crohn’s disease, or ease pain and other symptoms of irritable bowel syndrome, according to a 2020 review of well-designed studies by the American Gastroenterological Association. “The best thing you can do is eat fermented foods and, ideally, lots of fiber,” Gilbert says. If you’re new to high-fiber foods, start small and build up as you feel comfortable to avoid gas and bloating, Wastyk adds.
Probiotics may not even be helpful at restoring gut bacteria wiped out by antibiotics. In a 2018 Israeli study, people who took probiotics after a course of antibiotics still had a disrupted microbiome five months later, while people who didn’t take probiotics saw a healthy bacterial balance return after three weeks. Eating fermented and fiber-rich foods is a better idea, Gilbert notes.
Are Personal Microbiome Tests Worth It?
Direct-to-consumer tests promise to analyze your personal microbiome, identifying the bugs in your inner zoo via a stool sample sent in, and explaining what they mean for your health. Experts say that while the results might be useful, the field of home microbiome testing may not be ready for prime time.
The price tag: Tests costs $99 to $450, with some companies also charging monthly fees ranging from $29 to $99.
What you get: Services vary wildly. Several use consumers’ basic microbiome data to upsell expensive “personalized” supplements. Other tests are sold by health care practitioners, who may offer their own pricey health consultations to explain test results and make recommendations. Still others are based on published research and use blood tests, blood-sugar tests, health questionnaires and food diaries in addition to microbiome testing to suggest diet and lifestyle changes.
Is it worth it? “You have to be a little cautious,” says Mayo Clinic gastroenterologist Joseph Murray, M.D. “While our science is moving along about what’s there [in the microbiome] and what it’s doing, we don’t know much about what’s good.” A recent editorial in the journal The Lancet voiced similar concerns. “Perhaps the most substantial problem is that there is no consensus regarding what comprises a healthy microbiome. The microbiomes of healthy people vary as much as their fingerprints,” write researchers from Australia’s Deakin University. “The known unknowns of the microbiome are staggering: approximately 20 percent of bacterial gene sequences have not been identified and 40 percent of the 10 million genes remain unknown with respect to their function.”
Still want to try it? “The thing to look for is if the company can give you actionable advice,” says University of California San Diego microbiome researcher Jack Gilbert, who has worked as a consultant for a microbiome testing company. “If they claim they can, see if their advice is backed by scientific evidence.”