Does Heat Kill Probiotics? Yes. Does It Matter? Maybe Not

Keeping Probiotics Chilled at All Times Probably Isn’t Super Critical

• Heat-Killed Probiotics Can Be Just as Effective!|
• Why Would You Deliberately Inactivate Probiotics?|
• The Reason Dead Probiotics Can Still Work|
• Forgetting to Refrigerate Your Probiotics May Not Hurt|
• Shelf Stable Probiotics|
• Does Heat Kill Probiotics? A Recap|

If probiotics are part of your health and wellness regimen, you may have wondered if you’re going to wipe out the benefits of those live bacteria if you accidentally leave them somewhere too warm.

As a general rule, when probiotic cultures are subjected to temperatures of 120 degrees F and above they start to die off [1]. It’s the reason fermented foods such as kimchi, sauerkraut, and miso, marketed as containing “live” beneficial bacteria, can’t be exposed to high heat during the cooking process.

Similarly, many probiotic supplements are sensitive to heat, and have storage instructions that recommend refrigeration.

This can lead to anxiety if you’re traveling with probiotics, if they sit on your porch on a hot day, or if you just forget to put them back in the refrigerator for a few hours.

However, I’m going to bring you some good news here, because the question of whether heat kills probiotic bacteria is actually much more nuanced than just heat = dead bacteria = no probiotic benefits. 

For a start, we now know from research that good bacteria can still have benefits even when deliberately inactivated by heat (heat-killed). Secondly, technology means many live probiotics are now actually fairly robust outside of a refrigerator.

Let’s dig into this intriguing subject some more.

Heat-Killed Probiotics Can Be Just as Effective!

We’re all used to hearing that probiotics must be alive to be effective, which sounds completely logical. But, strange as it might seem, there’s actually a lot of evidence that shows deliberately killing probiotics with heat doesn’t change their efficacy most of the time.

In fact, a systematic review of 40 randomized clinical trials (RCTs) that compared heat-killed probiotics to placebo, the same living probiotic strain, or other therapies, found that dead probiotics were about as good as living probiotics for preventing and treating disease [2]. 

You can hear me talk more about this fascinating systematic review in this video, but the key points are below:

• Killed probiotics were similarly effective to living probiotics in 86% of disease prevention trials and 69% of disease treatment trials.

• Killed probiotic strains were significantly more effective than living probiotics in 15% of disease treatment trials. 
• In another 15% of disease treatment trials it was the other way around (live probiotics were more effective than killed ones)

• Killed probiotics were effective in conditions including irritable bowel syndrome, diarrhea, eczema, allergies, infections, and obesity).
• 4 RCTs that were part of the systematic review suggested that killed L. acidophilus can effectively treat acute diarrhea in children.

Beyond this systematic review, several other studies (RCTs) support the consensus that deactivated or therapeutically heat-killed probiotics can have benefit [3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13].

A selection of these is shown in this summary table:

Why Would You Deliberately Inactivate Probiotics?

Let’s back up a little bit and ask, why would researchers be heat-treating living bacteria to kill them when it’s always been thought that to be active a probiotic product must contain viable live cultures?

The short answer is that historically, in some, very rare cases, live probiotics proved problematic for people who were very sick or very weak — in particular premature infants or critically-ill people who were immuno-compromised.

In these patient groups, there’s a small chance that live microbes may cross from the intestine to the tissues and blood, where they could cause an infection (outside of the digestive tract is not a good place for probiotics, or any part of the gut flora, to be) [14, 15].

Sterilized heat-killed probiotics were originally created to see if the benefits of probiotics could be replicated in very vulnerable populations without any worry about such side effects. Heat-killed bacteria are made by heating the bacteria to 158–250°F for at least 20 minutes in a lab before further sterilizing and processing [3, 4, 6, 13, 16]. 

Surprisingly, as we have seen, they proved remarkably effective in several clinical studies, not only in vulnerable people but also in the vast majority of people who can tolerate standard live probiotics perfectly well.

The Reason Dead Probiotics Can Still Work

After probiotics have been inactivated by heat, the dead bacterial cells release components such as lipoteichoic acids, peptidoglycans, and exopolysaccharide, which can still exert beneficial effects, in particular [17]:

• Modulation of the immune system
• Neutralization of pathogens

“Postbiotics” is a name you might hear used to describe heat-killed probiotics and their breakdown products and metabolites.

Killed Probiotics Can’t Grow (But It Might Not Matter)

Effective live probiotics, while not necessarily persisting long-term in the gut, can hang around long enough (a few days or so) to be metabolically active (beneficially altering the gut microbiome environment around them). They may even grow and divide to temporarily boost good bug numbers in the gastrointestinal tract. 

However, there is zero chance that heat-killed bacteria will be able to colonize the gut (i.e. grow and replicate there) even transiently. With a rapidly developing body of research that continues to tighten the link between our overall health and the gut microbiome, the inability of heat-treated probiotics to colonize the gut is enough to make us pause. 

Remarkably, similar to live bacteria, heat-killed probiotic strains can positively shift the composition of the gut microbiome [11, 12, 13]. This suggests that being alive is not a necessary requirement for a probiotic to trigger therapeutic changes in the gut flora. However, the degree to which these microbial shifts actually affect human health — and if they are comparable to live probiotics — is still up for debate.

For now,  heat-killed probiotics are not widely available commercially anyway and I don’t think there would be much benefit for the vast majority of consumers to intentionally seek them out over live probiotics if they were. Remember, the vast majority of studies showing benefits of probiotics on digestive health conditions like irritable bowel syndrome, bloating, inflammatory bowel disease (IBD), and small intestine bacterial overgrowth (SIBO) have all been done using traditional live probiotics.

Forgetting to Refrigerate Your Probiotics May Not Hurt

Now I’ve shown you the evidence that heat-inactivated probiotics can still have health benefits, it may shed a different light on the concerns that most of us have when we don’t keep our traditional probiotics cold all the time.

While I’m not recommending that you deliberately keep your probiotics outside of the fridge, there is likely to be a lot more leeway for short-term storage at high temperatures. 

For example, If you are traveling without access to refrigeration, or if your probiotics arrive through the mail on a hot day, I think we have enough information to say that this should not be a concern. The bottom line is that if some of the bacteria do die, they will probably still be effective anyway.

Similarly, if you are using a probiotic powder and pouring it into a hot tea or coffee or over a hot meal there should be no reason for concern [18, 19]. 

This is particularly the case for well-formulated probiotics with multiple strains of live microorganisms, some of which will often be more heat stable than others. High-quality probiotic products will tend to be manufactured with an overage of bacteria (more than stated on the label) to account for some loss.

However, to stay on the safe side and get the most out of your probiotics, taking them in a cool and neutral pH beverage like water is probably the best course of action.

Obviously, it should give you pause if a probiotic that was formerly working well does not appear to do so anymore. But simply leaving your probiotics out of the fridge overnight should not be enough for you to consider throwing out a valuable product that is almost certainly still going to be safe and effective.

Be Sensible

That said, bacteria that are deliberately heat-killed and sterilized are going to be different from those that get wiped out by spending hours in your parked car, or in a black mailbox in the height of summer (estimates suggest these could mean your probiotics getting to 147°F [20] and 136°F [21] respectively).

In these extreme situations, any type of probiotics can’t be guaranteed safe or effective and you need to use common sense [16, 22].

The bottom line? We don’t have a huge body of research to show what happens to heat-sensitive probiotics when they get too warm, so it’s best to follow recommendations on things like expedited shipping, chilling as soon as possible, and taking with a cooler temperature drink. 

If your probiotics happen to arrive warm or with a melted icepack, it’s likely not an issue, but it is always OK  to reach out for a replacement if you are genuinely worried about the viability of your probiotics.

Shelf Stable Probiotics

If you travel a lot or generally worry about the viability of their probiotics, choosing a shelf-stable product (such as Triple Therapy sticks) can offer extra reassurance.

Some ways probiotics can be made to be more shelf-stable (safe to keep at room temperature) include:

• Being packaged in single-serve packets that keep out moisture, light, and air.
• Containing naturally more heat-resistant strains (or strains that have been made more shelf-stable by physiological stressors) [23].
• Being freeze-dried while being protected by a cryoprotective agent (such as trehalose), in a way that ensures that the freezing process keeps the bacteria in stasis but doesn’t permanently destroy them [24, 25].

That said, “shelf stable” probiotics are likely to be just as sensitive to very high summer day temperatures as probiotics that are recommended to be kept refrigerated.

Does Heat Kill Probiotics? A Recap

Hopefully all the above information will leave you feeling more reassured about taking probiotics when you’re traveling, or consuming probiotics that haven’t been kept in the fridge permanently. Of course, you should strive to store your probiotics as recommended and use them within the given shelf-life but, if the worst were to happen and your probiotics became non-viable due to getting too warm, all the evidence points to them still having gut and immune system benefits.

My book Healthy Gut, Healthy You details an eight-stage plan to overhaul your gut health that includes probiotics supported by dietary changes and other relevant supplements. Should you be looking for more personalized support on repairing your gut and using probiotics you can also reach out to us at the Ruscio Institute for Functional Health.

The Ruscio Institute has developed a range of high-quality formulations to help our patients and audience. If you’re interested in learning more about these products, please click here. Note that there are many other options available, and we encourage you to research which products may be right for you.