What Are Probiotics?

Last Update: September 28, 2022

The Greeks gave us culture, language, and apparently probiotics. From the ancient root words “pro” (as in promoting) and “biotic” (meaning life), probiotics are literally life affirming.

And in fact, Greek yogurt is naturally full of these beneficial microorganisms, which perhaps explains why it’s become more popular than conventional yogurt in recent years. Apparently it’s not just about the John Stamos cameos in the commercials. More likely, it has to do with the fact that the medical community is starting to pay attention to probiotics and tout their many healing benefits—which range from soothing digestive disorders to boosting brain function.

Understanding bacteria in the human body

The International Scientific Association for Probiotics and Prebiotics (ISAPP) defines probiotics as “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.” So, even though it might seem counterintuitive to put bacteria in your body on purpose, it’s clear to see how probiotics play a significant role in maintaining good health. In fact, many have made themselves at home with you since the day you were born. More than 500 known probiotics are native to the human body and are mostly concentrated to the gut where they live alongside neighboring “bad” types of bacteria. In general, you always want to have a higher concentration of good to bad bacteria (most doctors tout an 80/20 balance). When properly aligned, the healthy probiotics in your gut aid in digesting food and moving it through the intestines, keeping them healthy and also boosting the immune system. But, because there’s no real way to test the levels yourself, probiotic supplements and probiotic-rich foods are a convenient and reliable way to ensure a proper balance.

Probiotics vs. antibiotics

Probiotics are sensitive, and their colonies can be vulnerable to intruders, the most common of which are antibiotics. As you might have guessed, antibiotics are the opposite of probiotics. They’re introduced into the body for the necessary purpose of killing harmful bacteria when you have an infection (like when your doctor prescribes amoxicillin, a common antibiotic, to treat bronchitis). But antibiotics also take a toll on the good probiotic populations. This is why many people experience antibiotic-related diarrhea and yeast infections following a round of antibiotics, and why many practitioners suggest supplements like acidophilus and yogurt afterward in order to replenish the good bacteria.

On his blog, renowned physician Dr. Mark Hyman lists the potential problems that could happen if ratios of good to bad bacteria continue to be out of whack, including:

  • Heartburn
  • Bloating
  • Constipation
  • Chronic diarrhea
  • Excess gas
  • Inflamed joints
  • Eye problems
  • Allergies and asthma
  • Acne
  • Arthritis
  • Headaches
  • Autoimmune diseases
  • Candida infections
  • Depression
  • Attention deficit

Making the connection between some of these symptoms and bacterial inequities can be a stretch for many people—and even traditional doctors. Yet, the symptoms will persist until balance is restored and the body can begin healing on its own.

What’s wrong with our guts?

One of the bigger problems that comes from unbalanced bacterial environments is something called “leaky gut.” While it sounds gross, this medical mystery is something medical experts are just beginning to understand and connect to chronic conditions that are becoming more prevalent. Mostly studied by functional doctors and alternative medicine practitioners, the theory behind leaky gut syndrome is that a poor diet high in sugar, chemicals, and processed foods—combined with frequent use of medications and some parasites—can slowly damage the lining of the digestive tract and kill off good bacteria that need to thrive there.

The resulting permeability of the tract creates gaps that allow toxins, bacteria, and even undigested food to seep into the body, which triggers an immune response that can lead to a host of conditions, from irritable bowel syndrome (IBS) to diabetes to multiple sclerosis.

While there’s no official research to back up these claims yet, even the mainstream medical community acknowledges the importance of maintaining healthy gut bacteria for overall wellness.

Probiotic benefits

This is why taking daily doses of probiotics is important to continually help restore good bacteria counts. Research reveals that the most helpful probiotics come from one of two main groups: lactobacillus and bifidobacterium bifidum.


Lactobacillus acidophilus is the most common probiotic you’ll see on store shelves and is often added to food products. Acidophilus has been extensively studied and has been shown to affect many functions in the body, including aiding in digestion, treating IBS, reducing the symptoms of lactose intolerance, and preventing and curing vaginitis and yeast infections.

Lactobacillus casei, on the other hand, can help reduce the symptoms of lactose intolerance because it can live in environments that range widely on the pH scale. This makes it better enabled to do its job of breaking down sugar in the digestive tract to form lactic acid, even if a person has overly low (or acidic) pH due to lactose intolerance.

If you’re a frequent traveler, you’ll also want to be sure to pack Lactobacillus rhamnosus GG (often abbreviated L. rhamnosus GG) supplements, which have shown to be the most effective at shortening the duration of “traveler’s diarrhea.” Some studies even show that taking it regularly can prevent an episode completely.

Bifidobacterium bifidum

This common strain of probiotics is vital because it provides barrier protection throughout the digestive tract, and is therefore most recommended by practitioners who study leaky gut syndrome. Like lactobacillus, bifidobacterium support a healthy digestive system, and certain strains may boost the immune system and therefore aid in treating specific conditions.

Bifidobacterium longum can survive in high levels of gastric acid and are an important probiotic for immune support. Because bifidobacterium levels naturally decrease as you age, supplementation may be more important as you get older.

Bifidobacterium breve is similar to casei in its abilities to break down foods into lactic and acetic acids, and is a common addition to dairy foods. Meanwhile, bifidobacterium infantis is great for babies as it supports stomach health, digestion, metabolism, and overall well-being—but it’s great for older children and adults as well.

Choosing probiotic supplements

Finding the right probiotic supplement is a bit of a shot in the dark. While there are countless online resources for which probiotics are best for your particular ailment, the effectiveness will depend on your individual body and symptoms.

There are many catch-all probiotic products on the market. They contain a proprietary blend of several popular strains and may be a good starting place if you’ve never taken a supplement before. If you’re trying to alleviate a very specific symptom, like chronic diarrhea, talk to your doctor as he or she may recommend a higher dose of a single strain.

However, there are a couple of important things to always keep in mind:

Probiotics are active microorganisms, and it’s important that they remain so until they’ve passed through your stomach acid and reach your digestive tract. You’ll want to research the manufacturer to determine if their products meet these guidelines. Also, strains that are better equipped to live in gastric acid and a low pH environment are generally healthier for you and more likely to be active when they reach the final destination.

There are recommended dosages for supplemental probiotics. They are measured in colony forming units, or CFUs, which, according to the Power of Probiotics website, is described as “a bacteria or yeast that is capable of living and reproducing to form a group of the same bacteria or yeasts.” Based on general dosage guidelines, a healthy adult should choose a strain or blend that contains 10 to 20 billion CFUs, and children should take 5 to 10 billion CFUs. After a course of antibiotics, or if you are trying to cure a specific digestive-related issue, 25 billion CFUs or more may be taken.

Some manufacturers make even higher doses, but the general consensus is that more is not necessarily better when it comes to probiotics. A high-quality probiotic supplement that remains viable will reach its destination and recolonize even at lower doses. As always, you will want to consult with your doctor before starting any new regimen.

Over time, symptoms should begin improving, though the exact amount of time depends on each individual. Some of the things you may notice are improved digestion, regular bowel movements, and decreased bloating and flatulence. Women in particular may have fewer yeast infections after prolonged use. Eventually you may notice you get sick less often, too—all signs that your immune system is functioning optimally.

The best probiotic foods

Probiotics can also be found in many foods. While some manufacturers have been adding synthetic probiotics to foods in an effort to increase their healthfulness, there are plenty of tasty options that contain naturally occurring probiotics as well.

Fermented foods

With some fermented foods, such as yogurt, a healthy bacteria starter or culture is added to the mix to begin the fermentation process. With other foods, like sauerkraut and pickles, a natural fermentation process occurs and encourages the growth of healthful probiotic bacteria.

Some probiotic-rich foods include:

  • Yogurt (but read the label and avoid sugar- and preservative-filled brands)
  • Sauerkraut
  • Kefir
  • Lassi
  • Natto
  • Kombucha tea
  • Kimchi
  • Miso
  • Tempeh
  • Pickles
  • Olives

Try these quick and easy recipes for making your own fermented foods:

  • Sauerkraut: All you need is some cabbage, salt, and cheesecloth, and in a few days you’ll have a hearty bounty you can eat solo, pile on top of sausages, or add to salads.
  • Miso soup: It’s a staple at Japanese restaurants, but also easy to make at home, too, from just two ingredients—miso paste and water. (Add dried seaweed and tofu if you want the works).
  • Kefir: The latest fro-yo craze has put a new spotlight on this fermented milk, which some consider a cousin of yogurt, which is great for smoothies and on top of granola. With just four ingredients, you can make it yourself.

Other sources of probiotics

Probiotic boosts can be found in a couple of other foods, too:

  • Microalgae: Blue-green algae, spirulina, chorella all fall into this category.
  • Milk: Often L. casei is added to milk to aid in digestion for lactose-intolerant individuals.

Probiotics are also good for kids

Probiotics are generally suitable for both adults and children; some probiotic drops for newborns may even help reduce colic, acid reflux, and constipation in developing bodies (though it’s always best to check with your family doctor for an official opinion). While only small trials have been done, the findings are encouraging for pediatricians and parents struggling with these digestive issues common among babies, and will set them on a path of wellness from the very beginning.

Illustration by Karley Koenig

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