“Live and reaching the gut”——you’ve probably heard this phrase in lactic acid bacteria advertising countless times.

At the same time, there’s been growing talk in recent years about “heat-treated bacteria (dead bacteria) also being studied for their health-related functions.” Does it have to be alive to matter, or can dead bacteria still do something worthwhile? Questions like these have lingered around lactic acid bacteria for a long time.

In March 2026, a new study came out that sheds light on this question from a fresh angle. It’s collaborative research led by the Graduate School of Agriculture at Tohoku University, with participation from Shimadzu Corporation and Itoen. The paper is titled “Live and heat-treated Lactiplantibacillus plantarum induce distinct metabolic and immune responses in intestinal epithelial cells,” and was published in the peer-reviewed journal iScience (online March 31, 2026, DOI: 10.1016/j.isci.2026.115516).

The research pointed to something simple but genuinely intriguing. The same lactic acid bacteria may trigger different responses in intestinal cell models, depending on whether they are alive (live cultures) or heat-treated (inactivated cultures)——that’s the core finding.

In response to the long-standing debate over “live or dead bacteria,” this research offers a fresh perspective: “Rather than asking which is better, perhaps each type plays a different role.”

About This Article: This article is for informational purposes and does not guarantee the efficacy of any specific food, lactic acid bacteria, or supplement. Today’s research used an intestinal cell model (cultured cells) in experiments and has not been confirmed to produce the same effects in humans consuming these foods.

Research Background——Live or Dead Bacteria?

Let me first clarify a few key terms.

Probiotics are microorganisms that are expected to reach the intestines alive and support health functions. You’ll find them in familiar products like yogurt and lactic acid bacteria drinks.

On the other hand, postbiotics refer to bacteria that have been inactivated through heat treatment or similar processes, as well as compounds produced by bacteria. Even though they’re no longer alive, researchers are studying their potential health benefits——and interest in postbiotics has been growing in recent years.

There have been many discussions asking “Is it better to have live bacteria, or are dead bacteria okay too?” However, there haven’t been many studies directly comparing the same bacteria strain in both living and heat-treated states under identical conditions. This research is significant precisely because it conducted such a comparison using precise experimental methods.

A Precision Instrument: The Microfluidic Co-Culture Device

The research team used a special experimental device called a “microfluidic co-culture device.”

This is an apparatus that can cultivate intestinal epithelial cells (the cells covering the intestinal surface) together with lactic acid bacteria in very tiny channels. It can artificially recreate an environment very close to what exists inside the actual gut.

Normally, it’s difficult to co-culture living bacteria with intestinal cells. The bacteria multiply too quickly and damage the cells. However, this device successfully achieved co-culture of live lactic acid bacteria with intestinal cells while maintaining tight junctions——the close-contact structures between cells that form the intestinal barrier.

The research team continuously measured the electrical resistance of the cells to confirm that the intestinal barrier remained intact throughout the experiment. Precision intestinal modeling with live bacteria——this was the technology that made this research possible.

Live Bacteria Showed Metabolic Changes; Inactivated Bacteria Showed Immune-Related Changes

The bacteria used in this experiment was Lactiplantibacillus plantarum, a lactic acid bacterium commonly found in pickles and fermented foods and known as a plant-derived lactic acid bacterium.

Under the experimental conditions used, the intestinal cell model showed different responses to live versus inactivated bacteria.

Live lactic acid bacteria showed changes related to metabolic processes in the intestinal cells. It appears they may have influenced metabolism-related activities, such as how cells exchange energy and process materials.

Heat-treated lactic acid bacteria (inactivated cultures), on the other hand, showed changes in immune-related responses in the intestinal cells. When analyzed with a focus on immune-related reactions, different patterns were observed compared to the live bacteria.

Even though it was the same bacterium, the intestinal cell model showed different directional responses depending on whether it was alive or heat-treated. Rather than “which is superior, live or dead bacteria,” this result suggests the possibility that “both may play different roles.”

A New Perspective: “Selective Use”

The significance of this finding is quite practical.

Until now, “living and reaching the gut” had been presented as central to the value of lactic acid bacteria. But this research, by comparing the same bacterial strain, suggests that heat-treated bacteria may have their own unique functions.

The research team proposes a new perspective: “Use lactic acid bacteria selectively——as either live or inactivated cultures——depending on which functions we’re focusing on, such as metabolism-related or immune-related responses.”

For example, if you’re seeking metabolism-related benefits, choose live cultures; if you’re seeking immune-related benefits, choose inactivated cultures——different bacterial states chosen based on intended purpose. In the future, such product design might become possible.

This is valuable knowledge that could expand new options in the development of functional foods and supplements. However, keep in mind this is cell-level research using intestinal models, and it hasn’t been confirmed that humans eating these products would experience the same effects. Further research would be needed for real-world application.

What This Means for Those of Us Who Eat Fermented Foods

This research offers an interesting perspective for those of us who regularly consume fermented foods.

Miso, soy sauce, pickles, yogurt——fermented foods contain not just live lactic acid bacteria, but also bacteria that have been inactivated through heat or the passage of time. For example, miso soup is often eaten after heating, and some lactic acid bacteria drinks are heat-pasteurized.

It was easy to think, “Once bacteria are killed by heat, they’re pointless.” But in light of this research, it’s intriguing that heat-treated bacteria showed different responses in intestinal cell models compared to live bacteria. Whether alive or heat-treated, perhaps each form has its own value. That said, this remains an observation in cultured cells, and it hasn’t been shown that the same thing happens when humans eat these foods.

Of course, since this research didn’t use actual fermented foods, we can’t jump to conclusions like “drinking miso soup boosts immunity.” We need to be careful to keep things in proper perspective.

Still, the idea that it’s not an either-or choice between “live or dead bacteria,” but rather that “both have meaning,” seems to broaden our appreciation for fermented foods a little. It’s fine to be conscious of live bacteria, and it’s equally fine to enjoy heat-treated fermented foods. Both are part of our dialogue with our gut.

A Product of Japan’s Fermentation Research Tradition

This research is a fruit of collaboration——led by Tohoku University, a Japanese institution, and involving Shimadzu Corporation, a precision measurement equipment maker, and Itoen, a beverage company. It represents a true industry-academia partnership.

Using precision experimental equipment and successfully achieving something that was previously difficult——the co-culture of live bacteria with intestinal cells——represents an interesting technological advance. Japan is traditionally rich in fermented food culture, and it continues to produce important fermented science research at the scientific level as well.

Lactic acid bacteria——the microorganism most familiar to us. The fact that an intestinal cell model showed different responses to this bacterium depending on whether it was living or heat-treated reminds us anew of the depth of fermentation. There are surely many mechanisms still waiting to be understood in the microscopic world of bacteria.

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Whether alive or heat-treated, the bacteria showed different responses. The question has shifted——not from “live or dead,” but to “what differences exist?”

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From Toshi

Reading this research, I felt that lactic acid bacteria can’t be simply divided into “good because they’re alive” or “pointless if heat-treated.” Fermented foods like miso soup, which we eat after heating, might have aspects worth noting in their own way, different from live bacteria.

However, this research is an experiment using intestinal cell models, and it doesn’t mean that drinking miso soup will boost your immunity. I want to be careful to keep those things separate.

Both live bacteria and heat-treated bacteria likely have functions we still don’t fully understand. While enjoying fermented foods as part of my daily meals, I want to gradually pay attention to research like this as well.

※ This article is based on personal experience and publicly available information. It is not intended to diagnose, treat, or prevent any disease. If you have health concerns, please consult a doctor or registered dietitian. See our Disclaimer.