A few years ago, we introduced you to the “Superhero in Your Gut” – the trillions of bacteria, viruses, fungi, and other microorganisms living in your digestive tract, collectively known as your gut microbiome. Since then, the research has continued to reinforce just how important that little ecosystem is.

And, perhaps inevitably, an already enormous industry offering to make your superhero even more super has grown significantly during that time.

Walk through the supplement aisle today and you can find probiotics promising billions of “good” bacteria in capsules, powders, and gummies. Next to them are prebiotics designed to feed those bacteria. There are also synbiotics, which combine the two, because apparently your microbiome likes a combo package.

Some of these products can cost $30, $50, or considerably more per month and we’re buying them. Recent research found that the percentage of Americans taking probiotic supplements more than tripled during the past 15 years.

So, are they worth it? For most healthy people, most of the time, probably not.

First, Meet Your Microbiome

Your digestive tract is home to a remarkably complex community of microorganisms. We are still learning exactly what all of them do, but we know they help break down parts of food we can’t digest ourselves, interact with our immune system, and produce compounds that affect metabolism and inflammation.

One particularly important job happens when bacteria in your colon ferment certain carbohydrates and fibers that your own digestive enzymes can’t break down. In the process, they produce compounds called short-chain fatty acids. These help nourish cells lining the colon and are involved in regulating inflammation, blood sugar, metabolism, and appetite.

Your microbiome also interacts with your immune system and communicates with your brain. Researchers continue to investigate connections between the microbiome and everything from cardiovascular and metabolic health to mood and neurological function. The gut-brain connection is a very popular research topic.

Those studies continue to fuel the probiotics craze. But the craze may not be well-founded.

Finding an association between certain gut bacteria and better health doesn’t necessarily mean that swallowing those bacteria will produce better health. And having a healthy microbiome isn’t as simple as accumulating as many supposedly “good” bacteria as possible.

What seems to matter is having a diverse, resilient microbial community. And your community is influenced by your diet, medications, environment, age, genetics, and probably quite a few things scientists haven’t figured out yet.

But there is no solid evidence that simply adding more good bacteria does anything for your health.

What Exactly Is a Probiotic?

A probiotic is a live microorganism that, when consumed in an adequate amount, has been demonstrated to provide a health benefit.

That last part is important.

There are thousands of different species and strains of bacteria, and they aren’t interchangeable. Research showing that one particular strain helps with one particular medical problem does not mean another strain will do the same thing. It certainly doesn’t establish that a bottle containing a grab bag of “good bacteria” will make an otherwise healthy person’s gut healthier.

Yet that’s essentially how many probiotic supplements are marketed.

Probiotic supplements generally contain concentrated amounts of a relatively small number of bacterial strains. Once swallowed, those organisms have to survive stomach acid and the competitive neighborhood already occupying your intestinal tract. Even when they make it through, they don’t necessarily move in permanently.

More importantly, there is surprisingly little evidence that routine probiotic supplements improve overall gut health in healthy people.

Some research has even raised the possibility that indiscriminately adding bacteria isn’t always beneficial. In one Stanford trial involving people with metabolic syndrome, participants taking a multi-strain probiotic had strikingly different responses. Some saw improvements in blood pressure and triglycerides, while others experienced worse blood sugar and insulin responses.

That doesn’t mean probiotics are bad. It means biology is complicated, and “good bacteria” is not a sufficiently precise prescription.

When Probiotics Can Help

There are circumstances in which specific probiotics have evidence behind them.

Certain strains have been studied for particular gastrointestinal conditions and may help some people taking antibiotics by reducing the risk of antibiotic-associated diarrhea or C. difficile infection. Probiotics are also being studied for specific digestive disorders and other medical conditions.

But this is where it makes sense to treat a probiotic more like a targeted intervention than a daily multivitamin. The question isn’t simply, “Should I take a probiotic?” It’s “Is there evidence that this particular strain, at this particular dose, helps with the particular problem I’m trying to solve?”

If you’re considering one because of a medical condition, medication, or persistent digestive symptoms, talk with a medical provider rather than standing in the supplement aisle comparing numbers of billions of bacteria.

More isn’t necessarily better.

And Then There Are Prebiotics

Despite the similar names, prebiotics are something quite different from probiotics.

Probiotics are microorganisms. Prebiotics are substances that certain beneficial microorganisms can use as food. Most familiar prebiotics are types of carbohydrates that we don’t completely digest ourselves, allowing them to travel farther through the digestive tract where bacteria can ferment them.

This is an entirely sensible strategy: instead of trying to introduce a handful of new organisms into an ecosystem containing trillions of them, feed the helpful organisms already living there.

But that doesn’t mean you need a prebiotic supplement either.

Many of the foods we should be eating anyway are loaded with the fibers and other compounds our gut microbes like. Beans, lentils, whole grains, fruits, vegetables, nuts, seeds, onions, garlic, and artichokes all provide material for your microbial residents to work on.

And unlike a prebiotic powder, those foods arrive with vitamins, minerals, plant compounds, and other forms of fiber attached.

There is also an important technical distinction here. “Fiber” and “prebiotic” aren’t synonyms. To scientifically qualify as a prebiotic, a substance must be selectively used by microorganisms and have evidence that this produces a health benefit. But for the person standing in the grocery store, the practical message is considerably simpler: eat a wide variety of fiber-rich plant foods.

Your Microbiome Likes Variety

This may be the least glamorous conclusion ever produced by microbiome science: Eat your vegetables. And your beans. And fruit. And whole grains. And nuts and seeds.

Research consistently suggests that dietary diversity is associated with microbial diversity. Different microbes prefer different foods, so eating a wider variety of plants provides different types of fiber and other compounds for different microbial populations.

Fermented foods can help too. Yogurt, kefir, kimchi, sauerkraut, and other fermented foods can contain a variety of live microorganisms. In studies, diets containing fermented foods have been associated with increased microbiome diversity and changes in markers of inflammation.

One caution: “fermented” and “probiotic” aren’t technically the same thing. A food only qualifies as probiotic when it contains defined live microorganisms that have been shown to produce a health benefit. But you don’t need to worry about the terminology while eating your yogurt.

Why Food Usually Wins

Here’s the interesting disconnect.

While probiotic supplement use among American adults more than tripled between 2009 and 2023, researchers found very little change in how much fiber Americans ate. Average intake remained around 8.5 grams per 1,000 calories, substantially below the recommended 14 grams per 1,000 calories.

We have apparently decided that changing the inhabitants of our gut sounds easier than feeding them.

To be fair, it is. Taking a capsule every morning is much easier than figuring out how to get more beans, vegetables, and whole grains into dinner. But the capsule isn’t a shortcut to the same destination.

Food supplies a huge variety of substrates to a huge variety of organisms. A probiotic supplement generally supplies a large quantity of just a few selected organisms. Those are fundamentally different interventions.

There is also the supplement problem. As we’ve discussed before (Supplements: More Wild West Than Wellness), probiotics and prebiotics sold as dietary supplements are not required to go through the same FDA premarket approval process for safety and effectiveness as medications. Products can differ enormously in the strains they contain, the amount of viable organisms present, and the evidence supporting the claims on the bottle.

That doesn’t mean every supplement is ineffective or poorly made. It means a slick label containing words like “microbiome,” “balance,” and “billions of CFUs” isn’t evidence that the product will do anything useful for you.

The Gut-Healthy Shopping List

If you’re healthy and simply want to support your microbiome, you probably don’t need to add another expensive supplement to your morning routine.

Instead, think diversity. Try rotating the fruits and vegetables you buy rather than eating the same three every week. Add beans or lentils to meals. Choose whole grains more often. Snack on nuts and seeds. Add onions, garlic, herbs, and spices when you cook. If you like fermented foods, work yogurt, kefir, kimchi, or sauerkraut into your regular diet.

And increase fiber gradually. Going from very little fiber to a mountain of lentils and kale overnight may make your gut bacteria delighted, but the people sitting next to you considerably less so. Your microbiome needs time to adjust.

There are situations in which a specific probiotic or prebiotic may be useful. But that’s a medical question worth asking rather than a supplement habit worth assuming.

The best way to take care of the trillions of microorganisms already working for you is surprisingly inexpensive and remarkably unexciting: feed them well.