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What Are Probiotics?

By Mary Jo DiLonardo
WebMD Feature
Reviewed by David Kiefer, MD

Probiotics are live bacteria and yeasts that are good for your health, especially your digestive system. We usually think of bacteria as something that causes diseases. But your body is full of bacteria, both good and bad. Probiotics are often called "good" or "helpful" bacteria because they help keep your gut healthy.

Probiotics are naturally found in your body. You can also find them in some foods and supplements.

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It's only been since about the mid-1990s that people have wanted to know more about probiotics and their health benefits. Doctors often suggest them to help with digestive problems. And because of their newfound fame, you can find them in everything from yogurt to chocolate.

How Do They Work?

Researchers are trying to figure out exactly how probiotics work. Here are some of the ways they may keep you healthy:

  • When you lose "good" bacteria in your body (like after you take antibiotics, for example), probiotics can help replace them.
  • They can lower the amount of "bad" bacteria in your system that can cause infections or other problems.
  • They can help balance your "good" and "bad" bacteria to keep your body working like it should.

Types of Probiotics

Many types of bacteria are classified as probiotics. They all have different benefits, but most come from two groups. Ask your doctor about which might best benefit you.

Lactobacillus. This may be the most common probiotic. It’s the one you’ll find in yogurt and other fermented foods. Different strains can help with diarrhea and may help with people who can’t digest lactose, the sugar in milk.

Bifidobacterium. You can also find it in some dairy products. It may help ease the symptoms of irritable bowel syndrome (IBS).

What Do They Do?

Probiotics help move food through your gut. Researchers are still trying to figure out which are best for certain health problems. Some common conditions they treat are:

There is also some research to show they ease the symptoms of non-stomach-related problems. For example, some people say they have helped with:

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