A simple guide to probiotics — what they are, where to find them, and whether or not you should take them

• Probiotics are live bacteria that are intended to have health benefits.
• They may help with diarrhea and IBS, but the evidence for other benefits is still lacking. 
• Experts told INSIDER you shouldn't take a probiotic supplement just because. If you're happy with your gut health, skip them.
• The jury's still out on the health benefits of different fermented foods, too. But you should eat them if you like the taste and tolerate them well.

Stumble into any drugstore or supermarket and you'll find shelves full of supplements and food products touting their probiotic content as a way to "boost" your gut health. 

But a deeper look at the research on probiotics — the collective name for a whole swath of purportedly beneficial bacteria — shows that they don't always live up to the hype.

INSIDER consulted two digestive health experts to learn more about probiotics. Here's what you need to know if you're considering adding them to your routine. 

Probiotics are friendly bacteria that are intended to have health benefits.

By now you've probably received the message that not all bacteria are bad. In fact, the trillions of bacteria currently living in your digestive tract — a group of bugs known as the gut microbiome — are important to your health. They help you digest food, produce vitamins, and kill off bad bacteria, according to the US National Center for Complementary and Integrative Health (NCCIH).

"Probiotics" is the catchall name for any live microorganisms that are intended to have health benefits, according to the NCCIH. You can get them in supplement pills, yogurt with live and active cultures, and in fermented foods that are made using live bacteria, like kombucha, kimchi, miso, tempeh, and sauerkraut. Whatever the source, the idea is that consuming probiotics will support the growth of good bacteria in your gut — and therefore improve your health. 

But probiotics might not live up to lofty expectations. 

First, the good news: There's evidence that probiotics can help treat infectious diarrhea (the kind caused by bad bacteria) and antibiotic-associated bacteria (the kind that happens as a side effect of antibiotic medicines), the NCCIH notes. They also may help with irritable bowel syndrome.

But there's also no strong evidence to show that probiotics can help with other conditions, the NCCIH adds.

Scientists have reviewed studies on using probiotics for eczema, preterm labor, gestational diabetes, bacterial vaginosis, Crohn's disease,  allergies in babies, ulcerative colitis, UTIs, vulvovaginal yeast infections, a certain type of pneumonia, and the common cold.

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In just about every instance, researchers conclude that there's not enough evidence to recommend probiotics as a treatment. So it's not surprising that the US Food and Drug Administration (FDA) hasn't approved probiotics as a way to treat or prevent any health issue.

This is all complicated by the fact that it's tough to make broad claims about probiotics. It's an umbrella term applied to many different types of bacteria that aren't all alike, the NCCIH explains. If one strain of bacteria happened to show a health benefit, a different strain might not. Some scientists have also noted that not all of the live organisms in probiotic pills may survive the trip from your mouth and actually colonize in the gut. 

That brings us to the first important takeaway:

If your digestive system is happy, you don't need to take probiotic pills.

"I tell people if they're happy with their gut and they're not having any complaints, they don't need to supplement because their own flora is taking care of business," gastroenterologist Lisa Ganjhu, a clinical associate professor of medicine at NYU Langone Health, told INSIDER. "Sometimes they will be told by their roommate or their girlfriend or their boyfriend at they have to take probiotics, they wind up taking them, and they wind up getting an angry belly because there's a disruption in their normal flora. I tell people, if you're happy, don't muck with everything."

Danielle Capalino, a registered dietitian who specializes in gut health, agreed.

"I don't think there's a reason that everyone should be taking a general probiotic just because," she told INSIDER.

And remember: Even if a supplement is available over the counter and seems innocuous, in certain situations it may cause side effects or interact with prescription medications.

The NCCIH says that, for healthy people, probiotics have a good safety record. If they do cause side effects, it's generally just a mild digestive issue like gas. But for people with existing medical conditions, they can have more severe side effects. So it's good practice to talk with your doctor before you start taking any new supplement.

Eat fermented foods if you (and your gut) like them.

There's also a lot of hype about benefits of fermented foods made with live bacteria, like kimchi. But we still don't really know if they'll reliably improve your health, as gastroenterologist Dr. John DiBaise explained in a 2016 issue of the Mayo Clinic Health Letter. Part of the problem, he wrote, is that it's difficult to know how much and what types of bacteria are in a fermented food — so it's difficult to know what benefits you might get. 

But that doesn't mean you can't or shouldn't eat them. Fermented foods can still have other good-for-you nutrients, Capalino said, so they can still be a good addition to a healthy, varied diet.

But it's also possible that your gut won't tolerate fermented foods very well, and that's fine, too. 

"There's no harm in taking yogurt or eating kimchi or sauerkraut if you like it," Ganjhu said. "But if you don't tolerate [fermented foods], that's your body rejecting it."

In other words: Don't feel like you need to eat fermented foods, especially if they make your gut unhappy. Eat them if you like them and they make you feel good. 

For more on probiotics, check out the NCCIH's in-depth guide.

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