Do Probiotics Work? Here’s What Science Really Says

Do probiotics work? If you’ve been reading the headlines lately, the media clearly thinks they don’t:

  • Probiotics Are Mostly Useless and Can Actually Hurt You
  • Do You Buy Probiotics? New Study Says They May Not Work For You And May Even Be Harmful
  • Unexpected Findings Cause Scientists to Rethink Probiotics
  • Probiotics Found To Be Ineffective For Easing Symptoms Of Kids’ Stomach Bugs

In light of all these news stories, I’ve received many emails asking if you should avoid probiotics altogether.

That’s why in this article, I’m going to explain what these studies really mean (based on the latest and greatest research) and clear up some confusion around probiotics in general. After reading this, I’m confident you’ll feel a little more confident about your knowledge of probiotics.

Probiotics: What They Are and How They Work

Probiotics are microorganisms that may provide certain health benefits when ingested.

How probiotics work inside your body is still a bit of a mystery to scientists. Evidence suggest that probiotics communicate with your body through “toll-like” pattern recognition receptors … but more research is needed to understand their specific mechanism of action in humans.

Why Should You Care About Probiotics?

You have around 40 trillion bacterial cells in your body at any given moment (compared to around 30 trillion human cells).

Many of these bacterial organisms live in your gut, or “microbiome”. Your microbiome is now considered an organ that serves many important functions:

  • Stimulating the immune system
  • Breaking down potentially toxic food compounds
  • Synthesizing certain vitamins and amino acids
  • Providing protection from pathogenic organisms that enter the body
  • Controlling and/or producing neurotransmitters like serotonin (your body’s chemical messengers that contribute to feelings of well-being and happiness)

The exciting part is, we’re in the very early stages of research about the microbiome and its potential impact on your health. The evidence as a whole is promising but of course there are exceptions …

Which Probiotics May Not Work, According to Research Studies

It goes without saying, but you should avoid probiotics that have not been approved by the FDA. The majority of these don’t have any efficacy and safety data to support them. Unfortunately, this applies to most commercially available probiotic supplement products on the market.

With that in mind, let’s look at some published studies that show which probiotics don’t appear to work for specific conditions:

Strain

A commercially available formulation containing 11 strains.*

Conclusion

Many people’s digestive tracts prevent certain probiotics from successfully colonizing them.

Discussion

Gregor Reid, a microbiologist at the University of Western Ontario who did not participate in the studies, questions the results and urges caution in interpreting data from just 15 people.

A commercially available formulation containing 11 strains.*
Many people can’t successfully colonize standard probiotics in their gut. The probiotic strains tested may not be helpful and actually may harm the gut microbiome following a course of antibiotics.

Lactobacillus strains, in particular, appeared to inhibit the “normal” commensal microbiota. However, several studies suggest that using certain strains of probiotics during antibiotic treatment does confer some benefit.

Lactobacillus and/or bifidobacterium species

The use of probiotics could lead to a build-up of bacteria in the gut causing brain fogginess. 

“Brain fogginess is very subjective, and different criteria are used to assess this. I don’t believe that SIBO has any relationship to what they are calling brain fogginess.” –Dr. Emeran Mayer, a professor of medicine at UCLA. 
Lactobacillus rhammosus
There was no meaningful difference in how long parents said their kids’ vomiting and diarrhea lasted.
This was a well-designed study that seems to show the probiotic strain Lactobacillus rhammosus (commercially sold as Culturelle) does not help with acute gastroenteritis (specifically, symptoms of stomach flu) in children.

My Interpretation of These Study Results

What you see above is just a small sampling of studies done recently. “Probiotics” are mentioned nearly 20,000 times on PubMed. There’s been a lot of research done showing the benefits (or lack thereof) of many probiotic strains.

If you’re considering a probiotic supplement, it’s up to you to do your own research and talk to your doctor about the effectiveness and safety of the strain you’re considering for your condition.

While probiotics are largely unregulated and definitely controversial, there are now hundreds of peer-reviewed, randomized, placebo-controlled trials that have demonstrated the safety and efficacy of a variety of probiotic strains.

You can find a decent list of peer-reviewed studies done on probiotics in this article or this one.

Probiotics are not, in the words of the BBC, “useless.” This is the age of sensationalist journalism, folks. Don’t believe every headline you read!

Let’s clear up a few more misconceptions while we’re at it …

Just Because One Study Found One or More Strains Don’t Work Doesn’t Mean ALL Probiotics Don’t Work

Remember, hundreds of human clinical trials have shown that probiotics can help you if you suffer from conditions like IBS, skin disorders, anxiety, rheumatoid arthritis, depression, and more.

Probiotics May Not Always Colonize In Your Gut, But That Doesn’t Mean They Don’t Work

Some studies suggest that probiotic strains that are able to survive the harsh conditions in your stomach and make it into your intestinal tract are the ones that convey the most benefit.

However, even when probiotics do not colonize in your gut, they still may have an impact on your gut and immune health.

Are Fermented Foods the Same as Probiotics?

No. I personally love fermented foods. I use sauerkraut, drink kombucha, and make my own pickles. And those foods are definitely good for you. But they’re not the same as probiotics. Here’s how the International Scientific Association for Probiotics and Prebiotics explains it:

do probiotics really work

More Strains Is Not Always Better

What’s more important is the type of strains, and making sure you’re choosing products with the correct amount of probiotic strains. Unfortunately, “50 billion CFUs” doesn’t mean anything if the strains haven’t been studied for safety and efficacy at that dose (most supplements have not).

This 2017 study found that the amount of probiotic bacteria contained in foods is often much lower than the effective dose shown in studies.

Probiotics Can Be Dangerous

Probiotics are mostly unregulated, which is a problem. Certain studies have reported probiotic-related deaths and others have shown adverse events may be underreported in clinical trials.

That’s why’s it’s so important to choose make sure the strain(s) you’re taking has been studied for safety and efficacy in peer-reviewed, placebo-controlled clinical trials.

There is likely a huge difference between the probiotic strains tested and validated in human clinical trials and the ones found on the average grocery store shelf.

Lucy Mailing, an MD/PhD student at the University of Illinois and a staff research associate for Kresser Institute.

Probiotics Are NOT a Replacement for a Nutrient-dense Diet

What we eat is still the primary determinant of a diverse microbiota composition, which has been shown to be a key factor in people with “healthy” microbiomes.

Exercise may also promote healthy gut flora.

Key Takeaways

To recap:

  1. Many foods claiming probiotic content don’t contain enough for health benefit.
  2. Eating fermented foods is good … but not the same as taking probiotics.
  3. More strains doesn’t always means better.
    • What’s more important is finding a product/strain that has been studied to treat the health condition you’re looking to improve (IBS, IBD, skin conditions, anxiety, depression, to name a few.
    • Taking probiotics that haven’t been studied for safety can do more harm than good.
  4. Talk to your doctor (preferably a gastroenterologist) about which probiotics you should be taking for specific health conditions.
    • Do your homework: make sure the strains have been studied for safety and efficacy too.
  5. Diet and lifestyle are still the most important determining factors of gut microbial composition.

And if you’re going to use a probiotic supplement, here’s another resource that may help you:

The Best Probiotics, According to Science

 

*The 11 strains listed in studies #1 and 2 above were Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus casei subsp. paracasei, Lactobacillus plantarum, Lactobacillus rhamnosus, Bifidobacterium longum, Bifidobacterium bifidum, Bifidobacterium breve, Bifidobacterium longum subsp. infantis, Lactococcus lactis, Streptococcus thermophilus

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