What are Probiotics Benefits, Dangers, and Best Sources?

Depending on the species of probiotic microorganism, they can help protect us from just about everything -- from digestive disorders and infections to infertility and cancer -- with a minimal risk of side effects.

What are Probiotics Benefits, Dangers, and Best Sources

Probiotics benefits are getting lots of attention these days and probiotic products are taking the health and medical communities by storm.  In fact, 3.9 million US adults have reported using probiotics.  It’s only fitting we explore the science behind it and sort fact from fiction.

Last Updated: July 31, 2019

It sounds like the premise of a sci-fi story: “benevolent microscopic creatures living in and on human bodies are responsible for keeping people healthy.”  (Wait, come to think of it, that is a sci-fi plot!  A Wind in the Door by Madeleine L’Engle!  I haven’t thought about that book in years…)  

But we live in an amazing world where this concept is actually our reality.

Over the past couple of decades, researchers have discovered that the trillions of bacteria, viruses, and fungi covering every inch of the human body (collectively referred to as your “microbiota”) aren’t harmless little stowaways catching a free-ride like we thought they were.  Actually, they seriously affect how your body works.  As in, your body cannot work properly without their help.

You genuinely cannot be healthy unless these microscopic creatures living in and on you!  

As strange as it is to wrap your brain around, this discovery is also really exciting.  Suddenly, there are literally trillions (play the joke sound effect please!) of new ways to help improve your health.   

One of the most straightforward of these new ways is the use of probiotics.

What are Probiotics?

Probiotics are lotions, creams, pills, powders, capsules, or foods that contain microorganisms you find naturally in the human microbiota.  Most contain just a single species of bacteria but a few contain multiple bacteria or types of fungi.

These products bring healthy bacteria or fungi right to the places in your body where they should naturally live (be it skin, gut, or genital tract).  Once there, these little creatures act as if they had been born there.  They get to work doing what they do best: keeping your body healthy.

How Do Probiotics Help Your Body Stay Healthy?

Unfortunately, it doesn’t appear there is a single, overarching answer for how probiotics help you stay healthy.

Probiotics protect against many types of conditions. And each of them seems to involve a slightly different mechanism (or mechanisms).  

So, to really understand the health benefits of probiotics, we’ll have to look at their effects one at a time.  So, top off your coffee and squish around to find a comfy spot and let’s get going.  



Here we go!

Gut Disorders

loose stools

Taking oral probiotics has been shown to reduce symptoms of multiple gut disorders, including:

  • inflammatory bowel disease
  • irritable bowel syndrome
  • constipation
  • diarrhea

Researchers believe there are two main ways probiotics improve gut health:

  • probiotics introduce extra healthy probiotic microorganisms — extra healthy bacteria in your digestive tract takes room and food away from nasty bacteria, like E. coli or H. pylori, that could try to make a home in your gut.  Since gut infections can cause unpleasant GI symptoms and promote conditions like inflammatory bowel disease (IBD) or irritable bowel syndrome (IBS), taking probiotics to kick dangerous bacteria out of your gut can help keep those conditions at bay.
  • probiotic bacteria in probiotics make a group of compounds called short-chain fatty acidsshort-chain fatty acids (SCFAs) help keep the walls of your intestines from becoming “leaky”. Having a leaky gut is believed to be important in the development of IBD, IBS, constipation, and diarrhea.

Related Reading: Digestive Enzymes vs. Probiotics: What’s Better for Digestion?


Another well-studied effect of probiotics is their ability to prevent infections.  I already mentioned the ability of oral probiotics to prevent infections directly in the gut but this protective effect is not restricted to the GI tract. 

Probiotics boost immunity throughout your body.  For example, the use of probiotic lotions can help prevent skin infections.  And vaginal probiotics can prevent bacterial vaginosis, yeast infections, and urinary tract infections.  

All of these effects are thought to be the result of competition between healthy probiotic microorganisms and the infectious little buggers trying to attack your body.

Interestingly, though, there is a second way probiotics can help protect against infections, as well.

Remember the SCFAs I mentioned above?  Researchers now know that SCFAs also help the cells of your immune system function normally.  

SCFAs trigger immature immune cells living in your gut wall to mature. This gives your immune system more infection-fighting cells to work with. These extra immune cells then help your immune system fight infections everywhere in your body, even places as far away as your lungs.

Immune Disorders

Oral probiotics’ effects on immune function extend beyond helping you fight infections.  They are also able to prevent immune disorders, such as allergies and autoimmune diseases.

These effects are thought to come from the effects of SCFAs and another molecule, called histamine, on immune cell function.

SCFAs have been shown to help a specific group of immune cells, called “T-regulatory cells”, mature.  Like their name implies, T-regulatory cells regulate your immune system.  They are responsible for keeping your immune system from attacking anything except an actual infection.

And histamine has been shown to help keep a group of immune cells, called Th17 cells, from attacking your own body’s tissues. This nips autoimmune diseases in the bud.


probiotics can prevent obesity

A solid dozen studies have shown that taking an oral probiotic helps adults lose weight, an effect that can aid in the prevention or reversal of obesity.  Like most other conditions on my list here, it appears that there are a couple of mechanisms at play:  

  • probiotics can displace “obesity-promoting” bacteria — “bad” bacteria actually make extra calories out of your food. They break down bits of food you would otherwise have flushed away.  This can result in you getting thousands, even tens of thousands, of extra calories each week. Of course, that makes it really hard not to gain weight!
  • probiotics help regulate your immune system — some of the chemicals made by an unhealthy immune system (particularly those Th17 cells) mess with your metabolism. They make it more difficult for your cells to burn fat, so you end up storing it instead.  By keeping Th17 cells in check, probiotics can make it easier for your metabolism to burn calories.

Metabolic Diseases

Since probiotics help protect against obesity, it’s probably not a huge surprise to you that they can also protect against metabolic disorders, such as:

  • diabetes
  • high cholesterol
  • high blood pressure
  • heart disease

Much of this may be attributed to the improved metabolic function and decreased weight mentioned above. But researchers have also found dozens of other possible interactions! (See the studies here, here, here, and here.)  

Dental Cavities

Though there is less direct evidence here than for some of the other conditions, probiotics are suspected to be able to help protect your oral health.  Bacteria in probiotic products are naturally found in the mouth, including on the surface of your teeth.  They produce chemicals believed to stop the bacteria that eat tooth enamel from setting up camp, protecting you from cavities.


probiotics can prevent osteoporosis

While the evidence supporting a role for probiotics in protecting your teeth is still kind of hole-y (see what I did there!), the evidence that they support the health of other bones in your body is pretty strong.  There are solid studies showing that taking an oral probiotic can help prevent osteoporosis.

Improvements in bone health are believed to be mediated by probiotic bacteria’s ability to:

  • make important vitamins — probiotic bacteria can produce vitamins involved in protecting bone health, such as vitamin D, vitamin K, vitamin C, and folate 
  • break down the fiber in your food — breaking up fiber in your food helps free up the calcium in your diet so you can absorb it better 
  • calm overactive Th17 cells — overactive Th17 cells produce chemicals that cause your bones to be actively broken down

Colon Cancer

Oral probiotics may protect against certain types of colon cancer.  In fact, probiotics do an amazing number of things that may be able to keep cancer from developing in your gut.  Research indicates that bacteria in probiotics can:

  • deactivate mutagens — mutagens are chemicals that damage DNA in your cells, causing them to turn into cancer cells.  Probiotic bacteria in your gut can bind to these chemicals (that you, usually, swallowed with your food) and break them down before they can come into contact with your intestinal cells.
  • lower the pH of your colon — when the bacteria in probiotics break down food for energy, they produce organic acids (those SCFAs). These acids make the fluid inside the colon more acidic.  This is helpful for preventing colon cancer because conjugated bile acids, a powerful type of mutagen, cannot form in acidic environments.
  • keep your colon cells fed and healthy — colon cells can actually use SCFAs for energy, just like they use sugar.  By making SCFAs, probiotic bacteria help ensure your colon cells are well-fueled and healthy. This lets them repair themselves if they do come into contact with a mutagen.
  • slow down how quickly your colon cells divide — finally, research indicates SCFAs can actually slow down how fast cancer cells grow (i.e. how quickly you get an actual tumor from a single cancer cell and how fast it spreads).  This is thought to be because SCFAs turn on enzymes in colon cells that control which of their genes are turned on and off.  These enzymes can turn off genes that can make cells grow and divide too quickly.

Poor Muscle Function/Mobility

A few studies have shown that taking an oral probiotic boosts muscle function. Researchers believe this is because of those cool genetic effects of SCFAs I mentioned above in the context of colon cancer.

SCFAs made in your gut are actually absorbed by your body and flow through your bloodstream.  If they make it into a muscle cell, they can activate those important gene-regulating enzymes.  In muscle cells, these enzymes turn on the genes that let the cell:

  • burn fat faster
  • burn sugar faster
  • use oxygen more efficiently

All the things muscle cells need to work perfectly!  

Related Content: How to Improve Muscle Health [An Expert’s Guide]

Mental and Neural Disorders

probiotics can improve mental and neural disorders

Oral probiotics can positively influence brain and nerve function, reducing the symptoms of anxiety, depression, and migraines.  They are also strongly suspected to be helpful for managing autism symptoms.

Researchers think the effects of probiotics on your mental health is likely the result of probiotics’ ability to change the balance of chemical messengers in your brain.  

Probiotic bacteria increase levels of two specific chemical messengers, dopamine and serotonin, helping your nerves communicate with one another properly, preventing neural and mood disorders.

Male Reproductive Disorders

Men who consume probiotics may be protected from infertility and prostate cancer.  This is because probiotic bacteria help lower estrogen levels in the body. Keeping levels low prevents a condition called “estrogen dominance”, which drives both infertility and prostate cancer in men.

How do probiotic bacteria prevent estrogen dominance?

It’s a little complicated but, basically, probiotic bacteria keep estrogens in your intestine (which got there either from food you ate or from your body trying to dump them out into the toilet).  They don’t let your body absorb them.

By preventing your body from absorbing estrogens, probiotics keep estrogen levels in your body at a low, healthy level.  

Female Reproductive Disorders

Last, but most definitely not least, probiotics can also help protect female reproductive health.  Probiotics have been shown to be able to improve the symptoms of and/or risk for:

Don’t forget that probiotics may also be useful for your baby’s health after birth! Learn more about the Best Probiotics For Toddlers’ Immune Systems and the Best Probiotics for Kids.

Breast Cancer

probiotics can prevent breast cancer

Researchers also suspect probiotics may be able to help protect against breast cancer. There are a couple of reasons for this.  

  • probiotics reduce estrogen levels — just like prostate cancer, many breast tumors are driven by excess estrogen in the body.  Since probiotics can lower estrogen levels, they may be able to help keep breast cancer under control.  
  • probiotics prevent the creation of conjugated-bile acids — many breast cancers appear to be triggered, in part, by a buildup of conjugated-bile acids, those powerful mutagens I mentioned above that promote colon cancer, in breast tissue.  It turns out that these cancer-promoting compounds can be absorbed into your body from the gut and, for whatever reason, like to concentrate in breast tissue.  By reducing the levels of conjugated-bile acids made in the gut, probiotics should be able to protect breast tissue from these mutagens.

Unfortunately, there haven’t been enough studies done yet to tell for sure if this theoretical protection against breast cancer pans out in real life.

Are Probiotics Safe?

Man, is that a lot of health benefits!  You’ve got to be asking yourself right about now: “Alright, but what’s the catch?”

“Do probiotics come with all kinds of weird side effects?  Are they addicting?  Are they really easy to overdose on?  Do they make all of your hair fall out?”

Nope, nope, nope and nope!

In fact, in general, there is no catch.  Researchers and doctors agree that, for most healthy people, there is minimal risk of any side effects whatsoever.  They aren’t even usually associated with a risk of short-term constipation or diarrhea when people first start taking them, which one really might have expected.

There are a couple of groups of people, though, for whom probiotics might be a bit risky. These are:

  • if you have an extremely weakened immune system (active AIDs symptoms, recent chemotherapy treatment, recent surgery), there is a risk that probiotics can cause an infection.  Even though probiotic microorganisms are good for you, they could still harm your health if they grow out of control, which they could theoretically do if your immune system is very weak.
  • if you have an active autoimmune attack going on in your gut wall, you may also be at risk of developing an infection with probiotic microorganisms.  This could occur if your gut wall is so inflamed and damaged from your immune system’s attack that large holes leading straight into your bloodstream have opened up.  (This is more likely to be the case if you’re experiencing blood in your stool.)  Such large holes could let probiotic microorganisms into your blood, which is very unsafe.
  • if you have kidney disease, there is a theoretical that risk probiotic products could damage your kidneys further.  Some studies have shown that probiotics cause changes in the ability of your kidney to filter urine and increased levels of kidney-damaging chemicals (like uric acid) in your blood.  Researchers aren’t sure why this might be, nor are they sure the increases are significant enough to be dangerous, even for those with severe kidney disease.  If you have kidney disease, though, you should be cautious until researchers know for sure.

If you have one of these conditions but think you would benefit from probiotics, talk to your doctor about it!  Your doctor can help you decide if the rewards outweigh the risks for you.

Does It Matter Which Probiotic You Take?

several types of probiotics on a white table

All those health benefits and (for most people) essentially no risk of side-effects?!  It’s amazing!  And if you’re all jazzed up now, raring to hit the store and find a probiotic, any probiotic, I totally understand!  

But hang in there with me for just a little bit longer because not all probiotics are created equal.  There are only a few species of probiotics that have been proven to actually be helpful in humans.  And among the microorganisms researchers know are probiotics, not all of them offer all of the health benefits we just covered.  

In fact, there is typically just a handful of probiotic species that provide any given health benefit.  Check out Table 1 to see which probiotics really work for the health benefits you’re most keen on reaping!

Table 1: The Best Probiotic Species for Addressing Individual Conditions


Proven Beneficial Probiotic Species

Gut Disorders

Lactobacillus casei, Lactobacillus plantarum, Lactobacillus acidophilus, Lactobacillus delbrueckii bulgaricus, Bifidobacterium longum, Bifidobacterium breve, Bifidobacterium infantis, Streptococcus salivarius


Lactobacillus acidophilus, Lactobacillus plantarum, Lactobacillus reuteri, Lactobacillus rhamnosus, Lactobacillus salivarius, Enterococcus faecium, Saccharomyces boulardii, Lactobacillus casei rhamnosus

Immune Disorders

Lactobacillus acidophilus,* Lactobacillus casei, Lactobacillus fermentum Lactobacillus rhamnosus,* Lactobacillus reuteri, Bifidobacterium bifidum, Lactobacillus paracasei, Bifidobacterium longum, Bifidobacterium animalis


Enterococcus faecium, Streptococcus termophilus, Lactobacillus JBD301, Lactobacillus planetarum*, Lactobacillus gasseri*, Lactobacillus reuteri*, Lactobacillus acidophilus, Lactobacillus casei, Pediococcus pentosaceu, Bifidobacterium lactis*

Metabolic Disorders

Lactobacillus acidophilus*, Lactobacillus rhamnosus, L. plantarum WCFS1, Bifidobacterium bifidum, Lactobacillus bulgaricus, Bifidobacterium lactis Bb12, Bifidobacterium longum*, Enterococcus faecium

Dental Cavities

Lactobacillus rhamnosus, Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus paracasei, Lactobacillus reuteri, Lactobacillus johnsonii, Weissella cibaria, Streptococcus salivarius  


Lactobacillus helveticus

Colon Cancer

Lactobacillus casei

Neural and Mood Disorders

Lactobacillus helveticus R0052, Lactobacillus casei, Bifidobacterium longum R0175

Poor Muscle Health

Lactobacillus acidophilus, Lactobacillus rhamnosus, Lactobacillus casei, Lactobacillus plantarum, Lactobacillus fermentum, Bifidobacterium lactis, Bifidobacterium bifidum, Streptococcus thermophilus

Male Reproductive Disorders

Lactobacillus paracasei

Female Reproductive Disorders

Lactobacillus delbrueckii, Lactobacillus fermentum, Lactobacillus rhamnosus GR-1*, Lactobacillus fermentum RC-14, Lactobacillus acidophilus, Bifidobacterium lactis Bb12

* Species appears frequently in studies that show an effect

Found what you’re looking for?  (You probably landed on something containing at least Lactobacillus acidophilus, Lactobacillus rhamnosus or Lactobacillus casei, huh?  They are everywhere on that list!)

Now, if you were to hit the store, what do you need to buy to actually get that probiotic.  Well, you could either buy naturally probiotic-rich foods or find yourself a probiotic supplement!

Learn More: The Best Probiotic Supplements for Leaky Gut

What are the Best Natural Sources of Probiotics?

If you’re looking for probiotic-rich foods, you’re going to want to hit the “fermented foods” section.

Fermented foods are whole foods (fruits, vegetables, beans, seeds, dairy products, etc.) that have had microorganisms added to them.  These microorganisms aren’t added to the food as a probiotic (like they are in probiotic-supplemented foods), rather they are added to keep the food from spoiling, or to change the flavor or texture.

Fermented foods that you can add to your diet to help increase your intake of probiotics include:

  • sauerkraut
  • vinegar
  • kimchi
  • tempeh
  • pickled vegetables
  • miso

One of the great upsides of fermented foods is that they are whole foods. They come packaged with vitamins, minerals, fiber, and phytonutrients — all kinds of things that are good for your health, in general.  Plus, they are really tasty!

Unfortunately, fermented foods are rarely labeled with the exact concentrations of probiotic microorganisms in them.  Often, they may not even list the species of microorganisms that were added.  That can make things tricky if you’re looking for therapeutic doses of very specific species.

If you’re keen on knowing the exact dose and species (or if you really not of fan of any of those fermented foods), probiotic supplements may be a better choice for you.


What are the Best Probiotic Supplements for Men and Women?

Probiotic supplements come as pills, capsules or powders that contain one or more very specific strain of probiotic microorganisms.  

There are a ton of different probiotic supplements, though.  How do you know which one to pick?

Well, ultimately, you will have to determine which supplement is best for you, based on your goals and personal preferences.  But, if you’re looking for some inspiration, we used our handy little table above and some serious sleuthing to dig up some solid options to help get you started!

Best Probiotic Supplements for Men

Men, especially men who are considering having children, would do well to opt for probiotic supplements that contain Lactobacillus paracasei in order to reap fertility-protective effects from their probiotic.  Some solidly-rated supplements brands that fit the bill include Solgar Advanced, Naturelo, and Flora Revive.

Solgar Advanced 40+ AcidophilusNaturelo Probiotic SupplementOmniBiotics Flora Revive 100 Probiotic Supplement

Best Probiotic Supplement for Premenopausal and/or Pregnant Women

Premenopausal and/or pregnant women will likely want to ensure their probiotic supplement contains Lactobacillus delbrueckii and Lactobacillus fermentum.  The only brand we could find that contains both of these strains is Solaray’s Mycrobiome Probiotic Urgent Care.  Actually, this supplement contains every single one of the probiotic species shown to boost female reproductive health!

Mycrobiome Probiotic Urgent Care Solaray

Best Probiotic Supplements for Postmenopausal Women

Postmenopausal women, who are at high risk of developing osteoporosis, should keep an eye out for supplements containing Lactobacillus helveticus.  A couple brands we found that contain this strain include Garden of Life Mood +, Essential Probiotics, Jarrow Formulas Jarro-Dophilus EPS, and Probonix-Liquid Probiotic.

Garden of Life Probiotic and Mood SupplementEssential ProbioticsJarrow Formulas Jarro-Dophilus EPSAdult Grape Probonix

How and When Should You Take Probiotics?

Finally, you’ve got the probiotic you want to add to your routine!  Now, how do you take it?

Well, just like with picking the probiotic to begin with, this will depend.  When, how and how often you take your probiotic will be determined by:

  • your daily schedule
  • type of probiotic you are adding
  • whether you are trying to treat or prevent a medical condition
  • other medications and supplements you are taking

Since all of these factors are specific to you, we can’t tell you exactly when or how to take your probiotic.  There are a few general guidelines, though, that apply to most fermented foods and probiotic supplements that might be handy for you to keep in mind while deciding how to incorporate probiotics into your routine:

  • probiotics generally have to be taken every day to see serious health benefits — it can also take a long time to notice real differences in your health (weeks to months for the complete elimination of some symptoms), so be patient and know that you are doing something good for your health, even if it’s not immediately obvious.  (If after 3-4 weeks you are still not seeing signs your probiotic supplements are working, it may indicate that your probiotic isn’t working for you and you may need to adjust your routine.)
  • probiotics are thought to work better if they are taken on an empty stomach, but right before a meal — before breakfast is a practical option for a lot of people
  • probiotics can go bad — if the bacteria in your probiotic die, they can’t do their jobs in your body anymore!  Munching on fermented food or taking a probiotic supplement past their expiration date (or if there are visible signs they’ve gone bad) likely isn’t going to do anything for you.
  • it is always best to follow the recommended serving size — be sure to talk to a doctor or nutritionist before deviating from the instructions on probiotic supplement packaging

Take Home Message

Probiotics are one of the oddest, most unexpected health interventions.  Even 20 years ago, no one would have thought we would be using other organisms to make ourselves healthier!  

But healthier they do make us. 

Depending on the species of probiotic microorganism, they can help protect you from just about everything — from digestive disorders and infections to infertility and cancer — with minimal risk of side effects.  


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