Lactobacillus reuteri is a live bacterium found in some fermented foods and supplements that may support digestive and immune function

Lactobacillus reuteri (often shortened to L. reuteri) is a type of lactic acid bacterium that naturally lives in the human gut. Unlike many probiotics that are transient—meaning they pass through your system—L. reuteri appears to colonize, or establish itself, in your digestive tract for longer periods. It produces compounds like reuterin, which may help maintain the balance of your gut microbiome and support the barrier function of your intestinal lining.

You'll find L. reuteri in certain fermented foods, particularly some traditional cheeses, sourdough breads, and fermented vegetables, though the amounts vary widely depending on how the food was made and stored. It's also sold as a standalone supplement in capsule or powder form. The reason people seek it out is that emerging research suggests it may influence digestion, immune response, and even mood—though most of this research is still early and conducted in small groups.

Key Takeaways

  • L. reuteri is a bacterium that may stay in your gut longer than other probiotics and produce compounds that support digestive health.
  • You can obtain L. reuteri through certain fermented foods like some cheeses and sourdough, or through supplements sold in capsule or powder form.
  • Research suggests potential benefits for digestion, immune function, and gut barrier health, but most studies are small and ongoing.
  • The amount of L. reuteri in fermented foods is unpredictable, so supplements offer a more consistent dose if you want a specific amount.

What research suggests L. reuteri may do

Studies on L. reuteri have looked at several areas of health. In digestive function, some research indicates it may reduce bloating and improve bowel regularity, though the effect size varies between individuals. Other work has examined its role in supporting the intestinal barrier—the lining that controls what passes from your gut into your bloodstream—by promoting the production of mucus and tight junction proteins.

Immune function is another focus. Because a large portion of your immune system lives in and around your gut, researchers have studied whether L. reuteri influences immune response. Some animal and small human studies suggest it may support the production of certain immune cells, though translating this to real-world benefit in healthy people remains unclear. A few studies have also looked at mood and stress, with mixed early results, but this area is still very preliminary.

Most L. reuteri research has been conducted in laboratory settings, in animals, or in small groups of people. Larger, longer human studies are needed before strong claims can be made about what it does in everyday life. Individual response also varies—what helps one person's digestion may have little effect on another's.

How L. reuteri differs from other probiotics

Many probiotics are transient, meaning they survive your digestive system and exit your body within days or weeks. L. reuteri appears to be different: it can adhere to your intestinal cells and persist for weeks or months after you stop consuming it, which is why it's sometimes called a "colonizing" probiotic. This persistence may allow it to have a longer-lasting influence on your gut environment.

Another distinction is the specific compounds L. reuteri produces. While many probiotics produce lactic acid (which lowers pH and creates an environment hostile to harmful bacteria), L. reuteri also produces reuterin, a broad-spectrum antimicrobial compound. This may give it a different mechanism of action than, say, Lactobacillus acidophilus or Bifidobacterium species, though all are considered beneficial.

That said, L. reuteri is not necessarily "better" than other probiotics—it's straightforward different. Your individual microbiome, diet, and health status all influence which strains may be most useful for you. Some people may benefit more from L. reuteri, while others may respond better to a different strain or a mixed-strain product.

Where to find L. reuteri in food

L. reuteri occurs naturally in some fermented foods, though the presence and amount depend on the fermentation method, ingredients, and storage conditions. Traditional sourdough breads made with long, slow fermentation often contain it, as do some aged cheeses and fermented vegetables like sauerkraut and kimchi—especially if they were fermented at cooler temperatures for extended periods.

The challenge with food sources is predictability. A jar of store-bought sauerkraut may contain L. reuteri, or it may not, depending on whether it was fermented or straightforward pickled in vinegar, and how it was processed and stored. Raw, unpasteurized fermented foods are more likely to retain live bacteria, but they also carry a small risk of contamination if not handled properly. If you're interested in fermented foods for their general probiotic content, they're worth including in your diet—but if you want a specific dose of L. reuteri, a supplement is more reliable.

L. reuteri supplements: what to know before buying

L. reuteri supplements are sold as capsules, powders, and sometimes as chewable tablets. They're available over the counter at health food stores, online retailers, and some pharmacies without a prescription. The dose varies by product—some contain 1 billion colony-forming units (CFUs), while others contain 10 billion or more. There is no official recommended dose, so manufacturers set their own amounts based on the research they've reviewed.

When choosing a supplement, look for products that list the specific strain of L. reuteri (for example, ATCC PTA 6475 or DSM 17938), because different strains may have different effects. Check the label for a third-party testing seal from organizations like NSF International or USP, which verify that the product contains what it claims and is free of contaminants. Also note the storage instructions—many probiotics require refrigeration to maintain viability, though some shelf-stable formulations exist.

Cost varies widely, from a few dollars to $20 or more per month depending on the dose and brand. Since L. reuteri supplements are not regulated as strictly as medications, the quality and potency can differ between manufacturers. Starting with a lower dose and observing how you feel over a few weeks is a reasonable approach, since some people experience mild digestive changes when first taking probiotics.

Potential side effects and who should be cautious

For most people, L. reuteri is well tolerated. Some individuals report mild digestive symptoms when they first start taking it—bloating, gas, or a temporary change in bowel habits—as their microbiome adjusts. These effects usually resolve within a few days to a week. Drinking plenty of water and starting with a lower dose can help minimize this transition period.

People with severely compromised immune systems (such as those undergoing chemotherapy or with advanced HIV) should check with their healthcare provider before taking any probiotic supplement, including L. reuteri, because there is a theoretical risk of infection. Similarly, if you have a central line or other invasive medical device, your provider may recommend avoiding probiotics. Pregnant and breastfeeding people should also consult their provider, though L. reuteri is generally considered safe in these populations.

If you're taking antibiotics, probiotics are most effective when taken at a different time of day—ideally a few hours apart—since antibiotics can kill the live bacteria in the supplement. Once you finish your antibiotic course, resuming a probiotic may help restore your microbiome balance.

How to tell if L. reuteri is working for you

Because L. reuteri's effects are subtle and individual, there's no single marker that tells you it's working. If you're taking it for digestive reasons, you might notice changes in bloating, regularity, or how you feel after meals over the course of a few weeks. If you're interested in immune or mood effects, those changes are even harder to measure on your own and would require longer observation or formal testing.

A practical approach is to take the supplement consistently for 4 to 8 weeks and keep a straightforward note of any changes in how you feel—energy, digestion, mood, or other factors that matter to you. If you notice improvement, continuing it makes sense. If you see no change after a month or two, it may not be the right fit for your system, and you can try a different strain or approach. Remember that probiotics work best alongside a diet rich in fiber and whole foods, adequate sleep, and stress management—they're one piece of the puzzle, not a standalone solution.

Frequently Asked Questions

Is L. reuteri the same as the L. reuteri in baby probiotics?

Some infant probiotic products contain L. reuteri, often the strain DSM 17938, which has been studied for colic and digestive comfort in babies. The strain and dose are different from adult supplements, and infant products are formulated specifically for newborns and young children. Do not give an adult supplement to a baby; use only products labeled for infants.

Can I get enough L. reuteri from fermented foods alone?

It's possible, but uncertain. If you eat fermented foods regularly—sourdough bread, aged cheese, or fermented vegetables—you may be consuming L. reuteri, but you won't know the amount or whether the specific strain is present. If you want a consistent, measurable dose, a supplement is more reliable than relying on food sources.

How long does L. reuteri stay in your system after you stop taking it?

Because L. reuteri can colonize your gut, it may persist for weeks or even months after you stop consuming it, though the amount gradually decreases. This is one reason it's considered different from transient probiotics. However, individual variation is significant, and factors like diet and antibiotic use influence how long it remains.

Can I take L. reuteri with other probiotics?

Yes, many people take multiple probiotic strains together without issue. Some products are formulated with L. reuteri plus other strains. If you're combining separate supplements, start with one at a time to see how you respond, then add another if desired. This approach helps you identify which strain, if any, makes a difference for you.

Does L. reuteri need to be refrigerated?

Most L. reuteri supplements require refrigeration to keep the bacteria viable, though some newer shelf-stable formulations exist. Always check the label for storage instructions. If a product has been left unrefrigerated for an extended time, the potency may be reduced, even if the supplement still looks fine.