When you think of bacteria, your mind probably jumps right to germs and infections—but there’s more to these microorganisms than their bad reputation.

We have billions of bacteria living in our guts, and they don’t all lead to illness or disease. In fact, some of them are straight up good for us. “The bugs that colonize us are not just waste; they’re hugely important to our health,” says Neil Stollman, M.D., chairman of the Division of Gastroenterology at Alta Bates Summit Medical Center in Oakland, CA.

The good microorganisms in our digestive systems are called probiotics. Research suggests these bacteria may bolster our immune systems, keep us regular on the toilet, and even support our blood pressure and cholesterol, says Amy Gorin, M.S., R.D.N. The good bacteria hype is so real that about four million adults in the U.S. reported using probiotics in the past 30 days, according to the 2012 National Health Interview Survey.

Though many people take probiotic supplements, the bacteria are also found in a number of fermented foods and drinks, like yogurt and kombucha. But when it comes to these bacteria-packing eats, there are still a lot of questions out there: Which probiotic foods should you eat? Are all probiotic foods alike?

Read on to clear up some of your probiotic food confusion and get the most bacteria benefits from your diet.

When you’re looking to get a rich dose of probiotics from your grub, you’ll turn to fermented foods like sauerkraut, miso soup, tempeh, kimchi, kombucha, and yogurt. But not all of these foods are created equally.

“Not every single yogurt and sauerkraut contains probiotics,” says Gorin. Make sure a brand packs the good stuff by checking the label or visiting the company’s website for more information, she says. For instance, a yogurt containing probiotics will generally list “live active cultures” on the label. Some probiotic foods may even list the specific bacteria in them, the two most common being Lactobacillus and Bifidobacterium, according to the National Center for Complementary and Integrative Health. And when shopping for sauerkraut, specifically, look for an unpasteurized variety, since the pasteurization process can actually kill off probiotics, Gorin says.

From there, just how much good bacteria your yogurt or kombucha packs may vary quite a bit. “It’s hard to say for sure how many probiotics a specific food contains,” says Ryan D. Andrews, M.S., M.A., R.D., coach at Precision Nutrition and author of A Guide to Plant-Based Eating. That’s because a number of variables—like the strains of bacteria used in the food, how long it’s been fermenting for, and the temperature it’s been stored at—can determine a food’s total probiotic count, he says.

The good news: “In the naturally fermented food world, stuff like sauerkraut, kimchi, yogurt, kefir, tempeh, miso, and so forth all seem to be beneficial for health on some level, no matter the specific level of probiotics they contain,” he says. So, though there’s no one probiotic-packed food to rule them all, that sauerkraut or yogurt provides some benefit. (Just check that label!)

Though probiotics sure seem to be great for our gut, there is no ideal, universal recommendation for probiotic intake that has been backed by science yet, says Satish Rao, M.D., Ph.D., founding director of Augusta University’s Digestive Health Center. Researchers are still pinning down the specific benefits of individual types of bacteria.

Related: I Drank Kombucha Every Day For 2 Weeks—Here’s What My Gut Had To Say

Still, doctors take a number of factors—like whether you have ongoing stomach issues, are taking antibiotics, or are just an average person looking to maintain a healthy gut—into consideration when recommending probiotic foods or dosages of probiotic supplements, Rao says.

That said, if you’re healthy and want to supplement your diet with good bacteria, eating one or two servings of fermented foods daily is great for your overall digestion and colon health, he says. If you’re turning to probiotics because you’re having stomach issues, though, consult with your doctor first, since probiotics may not be the solution for whatever underlying issue you’re dealing with.

Given probiotics’ supreme popularity these days, companies are adding them to anything from frozen burritos to protein powder to breakfast cereal in order to increase their value. But the fact that a food contains probiotics doesn’t necessarily make it worth eating.

“Always look at the nutritional make-up of the food containing probiotics,” says Gorin. At the end of the day, brownies and ice cream that contain probiotics are still brownies and ice cream, and likely loaded with excess calories and sugar, both of which can lead to weight gain and other health problems when you eat too much, too often. Ask yourself: Would you consider this food healthy if there weren’t probiotics in it?

If you’re truly looking for a boost in good bacteria, stick with naturally-fermented foods, which are loaded with other nutritional perks like vitamins, minerals, fiber, and protein, says Andrews.

Sure, naturally probiotic-packed foods offer health benefits—but you won’t fully reap them if you’re eating a food that doesn’t agree with your system. Yep, we’re talking about dairy here.

Take kefir, for instance. This drinkable, yogurt-like food is loaded with probiotics, calcium, and magnesium, but if you’re lactose intolerant it’s probably going to cause discomfort like bloating, gas, or diarrhea, says Stollman. It’s not worth it to suffer through a slew of tummy symptoms in the name of probiotics!

If you find that your stomach is sensitive to dairy, just stick with dairy-free probiotic foods. Sip on kombucha, sauté some tempeh, or top the night’s protein with a spoonful of kraut. (If you’re really hung up on the kefir thing, there are brands out there made from coconut milk, says Stollman.)

While eating probiotic-rich foods has shown promise, a diet rich in a wide variety of nutrients is just as important for maintaining the countless types of healthy bacteria in your gut, says Stollman.

“Eating a diversity of fiber-rich foods, plant-based foods, and fermented foods, is probably the best way to fortify your biome,” he says. Perhaps the most important factor here is fiber, which acts as food for the probiotics in your gut. According to a review published in Microbial Ecology in Health and Disease, eating fiber can actually boost the number of probiotics in your body. So for optimal gut health, probiotic-containing foods should be just a part of an overall healthy diet rich in fruits, vegetables, and whole grains.

On the flip side, an unhealthy diet loaded with sugars and processed foods may actually negatively impact your gut health and microbiome, Stollman adds. Case in point: A study published in Nature suggests that drinking diet soda may actually mess with your gut bacteria so much that it could raise your risk for metabolic diseases like type 2 diabetes. So when it comes to making your gut microbiome happy, stick to that whole ‘let food be thy medicine’ thing.