When you think of bacteria in your gut, you probably get the heebie jeebies. But unlike illness-causing microorganisms, some types of gut bacteria are actually good for you. You’ve probably heard of probiotics — the “good bacteria” in your gut that assists in digestion and is found naturally in many foods, including yogurt, kimchi, kefir, tempeh, and miso, to name just a few.

When it comes to health issues, many people seek out natural solutions — and what’s more natural than the organisms that are already living in your digestive tract? Harnessing the power of probiotics has gotten hugely popular in the last 10 years, with many pills, bars, and yogurts now available. But what exactly do these supplements do?

According to the Mayo Clinic, studies are underway which may prove that probiotics help treat digestive system complications, diarrhea, IBS, yeast infections (both vaginal and UTIs), and even prevent or alleviate symptoms of colds or the flu (however, more research needs to be conducted for conclusive evidence).

Great, so you’re sold on probiotics. But if you’ve ever gone to your local health food store and stood in front of the myriad of supplement options, you know how difficult deciphering those labels and picking the right probiotic can be. To demystify shopping for probiotics, we spoke to Dr. Amy Shapiro of Real Nutrition NYC to figure out what we should be looking for.

Why supplements over probiotic-rich food?

“Probiotics are the healthy and good bacteria that live in our gut [that] help to prevent illness, disease, and assist in digestion and wellness,” Dr. Shapiro says. “Just like everything else, it is best to get nutrients from food, [so that] they are not altered or processed in any way, and you can see what you are eating.”

Like vitamins, probiotic supplements aren’t regulated by the FDA, so you might not know exactly what’s in there. You also might not know how your supplement has been transported — and since probiotics are actually alive, long transit times or years sitting in a warehouse could render your probiotic supplement ineffective. But despite these risks, there’s a reason many people still swear by supplements:

“Probiotic-rich foods aren’t usually part of most people’s daily diet,” says Dr. Shapiro. “So if you leave it just to food you may not get what you need.”

What should I look for at the store?

Any preexisting health issues — ones that you are probably trying to solve by taking probiotics — should guide which supplements you purchase. “If you are on antibiotics, if you have been sick, if you are suffering from chronic illnesses, or if you have candida (yeast overgrowth) will determine what you need,” Dr. Shapiro says. “These days some probiotic supplements are created for certain populations such as men or women over 50, so that may help you select what is right for you.”

Dr. Shapiro has a few recommendations on which strains of probiotics (there are at least 20 strains that are commonly ingested for health reasons) to look for to help with common problems:

1. Bifidobacterium infantis releases an acid that fights harmful gut bacteria, which helps with constipation and IBS.

2. Lactobacillus plantarum helps absorb calcium, produce hormones, and boost the immune system by producing L. lysine. It’s also beneficial for patients with IBS.

3. Bifidobacterium bifidum is a common probiotic and a jack-of-all-trades. It helps with digestive issues, but also plays a role in immune and allergy responses. This probiotic is also great for your skin.

4. Dr. Shapiro recommends Lactobaciliius bulgaricus for the lactose intolerant, as it neutralizes toxins and creates antibiotics.

There are many more strains, and deciding which one will depend on your body — here’s a helpful resource that breaks down 18 of the most popular probiotic strains.

Your dosage will depend on your body, but generally, look for at least 7 different bacteria strains and 5 billion CFU (a colony-forming unit, the biological unit of measurement for probiotics).

And since probiotics are living things, you should check the label to make sure it says “viable through end of shelf life.” Additionally, look for encapsulated supplements or delayed rupture technology. This will ensure that the bacteria survive the long journey through your body — you want to make sure they get to your intestines and aren’t broken down by stomach acid!

Dr. Shapiro’s favorite brand is Garden of Life. “They have many different strains available and they are kept in the refrigerated section of health food stores,” she says.

One last thing: Dr. Shapiro warns that taking two types of probiotics at once might effectively cancel each other out. And if you’re on an IV medication, undergoing chemo, or have had organ transplants or any portion of intestine removed, skip them completely.

Once you discover the right probiotics, you could be on the right path to the healthiest digestive tract you’ve ever had!

Christina Pellegrini is a writer and editor based in Brooklyn, NY. Her favorite things include Drake, athleisure, Beyoncé, lipstick, and succulents (in no particular order). According to Buzzfeed, her period is very metal. You can follow her on Twitter @theempireedit or read more of her writing on her website.

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