Probiotics are live bacteria that are considered “good,” or beneficial for your body’s functioning and your health. Many probiotics are similar to bacteria that are naturally living in your body. You may already be consuming some of these good bacteria if you eat fermented products, such as:

  • yogurt
  • some cheeses
  • some pickled vegetables

The concept of consuming more good microbes to aid health has been discussed since the early 1900s. The term “probiotics” is relatively new. It’s a combination of the Latin word for “for” and the Greek word for “life.”

Research has yielded promising results about the health benefits of probiotics. However, the science is not yet conclusiveon all the benefits of probiotics for healthy people or for treatment of particular diseases.

Today, many kinds of probiotics are commercially available in foods and supplements. As the National Center for Complementary and Integrative Health reports, some experts have warned that the rapid growth in probiotics marketing and use may have outpaced scientific research on the benefits.

Your bowels host an estimated 100 trillion microorganisms from more than 500 different species, according to Harvard Medical School. Your mix of bacteria is unique, like your fingerprint. Sometimes, illness or stress can change the bacterial balance and create digestive and other problems.

Probiotics work by changing the composition of your gut bacteria or the metabolic activity of existing bacteria. The good bacteria crowd out the bad in your intestine. This prevents the bad bacteria from multiplying and causing infection or inflammation.

For example, too much yeast in the body can lead to a yeast infection, but the well-balanced gut biome will keep yeast at lower levels.

Probiotics may help your digestion and enable your body to extract nutrients from your food. Good bacteria may also produce enzymes or proteins that inhibit, or even kill, harmful bacteria. Specific species of probiotics also stimulate your immune system.

Some bacteria are necessary for hormone production or vitamin (e.g., vitamin K) and nutrient absorption. Development of childhood type 1 diabetes may be associated with inflammation related to inadequate gut bacteria biome.

Research published by the American College of Gastroenterology indicates that particular species of probiotics may:

  • aid digestion
  • prevent diarrhea
  • ease vaginal infections
  • prevent autoimmune diseases
  • ease skin ailments
  • fend off urinary infections

But remember, not everyone responds in the same way to the same probiotic.

Some doctors advise you to use probiotics when taking antibiotics to combat a specific infection. This is because antibiotics kill off some useful bacteria along with the bad, which may cause diarrhea. The probiotics help maintain or restore a healthy balance in your gut.

Common genera of probiotics

The most commonly consumed probiotics are species of two main genera. These genera are also the most studied of probiotics:

Bifidobacteria: This genus of bacteria is commonly used in foods and supplements. They’re thought to:

  • support the immune system
  • limit the growth of harmful bacteria in the intestine
  • help break down lactose into nutrients the body can use

Lactobacillus: This genus of bacteria produces lactase, the enzyme that breaks down lactose, or milk sugar. These bacteria also produce lactic acid. Lactic acid helps control the population of bad bacteria. It also serves as muscle fuel and increases the body’s absorption of minerals. Lactobacillus bacteria are found naturally in the:

  • mouth
  • small intestine
  • vagina

Common species of probiotics

Probiotic species are genetic subtypes of genera. Each probiotic species has a different effect in the body. You will see the probiotic species names on food or supplement labels, combined with the genus name.

For example, the Bifidobacteria or Lactobacillus genus are often abbreviated as B. or L. and combined with the individual species name, such as acidophilus. This gives you the probiotic L. acidophilus. This is how the name will appear on food or supplement labels.

Here are six common species of probiotics that you’ll find on food and supplement labels.

B. animalis: This species is an ingredient in Dannon yogurt’s Activia product. It’s helpful in aiding digestion and fighting food-borne bacteria. It’s also thought to boost your immune system.

B. breve: This species lives in your digestive tract and in the vagina. In both places, it fights off infection-causing bacteria, or yeast. It helps your body absorb nutrients by fermenting sugars. It also breaks down plant fiber to make it digestible.

B. lactis: This is derived from raw milk. It’s an ingredient in Nestle’s probiotic infant formula, called Good Start Natural Cultures. It also serves as a starter for:

  • buttermilk
  • cottage cheese
  • other cheeses

B. longum: This species lives in your gastrointestinal tract. It helps break down carbohydrates and can also be an antioxidant.

L. acidophilus: This species is found in the small intestine and in the vagina. It helps digestion and may help fight off vaginal bacteria. You can find it in yogurt and fermented soy products, such as miso.

L. reuteri: This species is found in the intestine and mouth. One study showed that it decreased the oral bacteria that cause tooth decay. It’s also thought to help the digestive system.

How do you decide whether to add probiotics to your diet? A first step is to talk with a doctor to make sure they’re right for you. Probiotics are generally considered safe to consume, unless you have a compromised immune system or you’re seriously ill. Also, ask a doctor or pharmacist about dosage.

You may want to begin taking probiotics simply by adding some items with natural probiotics to your diet. You may want to keep a diary of what probiotics you introduce, and record over time whether you see any changes in your digestion or overall health. Some easily available food choices are:

  • yogurt
  • fermented cheeses, such as:
    • gouda
    • cheddar
    • Swiss
    • Parmesan
  • fermented vegetable products, such as:
    • miso
    • sauerkraut
    • pickles

If you want to take a probiotic dietary supplement, there are plenty of commercial products to choose from. Look for supplements that have:

  • Live cultures: Check the expiration date on the label. To be effective, the probiotic should be “live” when you take it.
  • Multiple bacteria species: A combination of probiotics is usually more effective than a single one.
  • Large enough quantities of bacteria to form colonies: This is measured in colony-forming units called CFUs.

It’s important to remember that probiotics are considered to be dietary supplements, which are not regulated by the Food and Drug Administration (FDA). Also, probiotic manufacturers do not have to prove claims of effectiveness, nor does the FDA monitor these claims.

The FDA is currently developing a method for discovering potentially harmful contaminants in probiotics.