According to Gram Research analysis, a two-strain probiotic combination of Lactobacillus acidophilus LA15 and Bifidobacterium animalis subsp. lactis Bi66 helped relieve constipation in mice over 21 days. The mice passed their first black stool sooner, moved food faster through the small intestine, and showed healthier gut bacteria and calmer inflammation. Human studies are still needed.
A new study published in 2026 in World Journal of Microbiology & Biotechnology tested whether a pairing of two probiotic bacteria could relieve constipation. According to research reviewed by Gram, the combination helped constipated mice pass their first black stool sooner, move food faster through the small intestine, and gain weight. The probiotic mix appeared to calm gut inflammation, strengthen the lining of the intestines, and encourage the growth of helpful gut bacteria. It also seemed to increase short-chain fatty acids, substances that gut bacteria produce and that help keep the colon healthy. Because the work was done in mice, it does not yet prove the same effects in people. Still, the findings add to growing interest in probiotics as a possible food-based way to support regular bowel movements.
Key Statistics
A 2026 study published in World Journal of Microbiology & Biotechnology found that constipated mice given a 1:1 mix of two probiotic strains passed their first black stool sooner than untreated constipated mice over 21 days.
The same 2026 mouse study reported that the probiotic mix increased several short-chain fatty acids, including acetic, propionic, butyric, and valeric acids, in the animals’ guts.
The Quick Take
- What they studied: Researchers asked whether a specific mix of two probiotic bacteria, Lactobacillus acidophilus LA15 and Bifidobacterium animalis subsp. lactis Bi66, could ease constipation and how it might work inside the gut.
- Who participated: The study used male laboratory mice of the KM strain. Constipation was caused in the mice with a drug called loperamide. The exact number of mice was not stated in the summary provided.
- Key finding: Mice given the probiotic pair had a shorter time to their first black stool, faster movement of food through the small intestine, and better weight gain. Their gut bacteria and inflammation markers also moved closer to healthy levels over 21 days.
- What it means for you: This is an early animal study, so it cannot tell you whether this probiotic will help you. If you deal with constipation, talk with a doctor before starting a probiotic, and treat it as a possible support rather than a cure.
The Research Details
The researchers split the mice into five groups. One group was healthy and received no drug. Another group was made constipated with loperamide and received no treatment. A third group received a standard constipation medicine for comparison. The last two groups were constipated and given low or high doses of the probiotic pair, mixed in equal amounts.
The treatment lasted 21 days. During this time, the team tracked how quickly food moved through the digestive tract, how often and how easily the mice had bowel movements, and their body weight. At the end, they examined the colon under a microscope and measured chemicals linked to inflammation, digestion, and nerve signaling.
The team also analyzed the mice’s gut bacteria by reading their genetic material and measured short-chain fatty acids, which are compounds made when gut bacteria break down fiber. Together, these measurements let them connect the probiotic’s effects on bacteria to changes in the gut lining and water handling.
Using a controlled setup with a healthy group, a constipated group, and a standard-medicine group makes it easier to see whether the probiotic itself caused the changes. Measuring many steps, from bacteria to inflammation to water movement, helps explain how the effect may happen rather than only whether it happens.
The study used multiple comparison groups and tracked outcomes over several weeks, which are strengths for an early-stage experiment. However, it was done in mice, and the summary provided does not list the number of animals per group, so the strength of the results is hard to judge. Results from mice often do not translate directly to people, so the findings should be treated as promising rather than conclusive.
What the Results Show
The clearest result was that the probiotic pair shortened the time it took constipated mice to produce their first black stool. Black stool in this type of mouse study is used as a marker that food has passed through the digestive tract, so a shorter time suggests faster movement through the gut. The mice also moved food farther along the small intestine, a sign that their digestive system was working more normally.
The probiotic also appeared to calm inflammation in the colon. Constipated mice had higher levels of inflammatory signals such as IL-6, TNF-alpha, and IL-1beta, while the probiotic lowered these and raised IL-10, a signal that helps quiet inflammation. The researchers also reported that the colon lining looked healthier under the microscope.
The probiotic pair seemed to repair the gut barrier, the thin protective layer that controls what passes from the intestines into the body. Treated mice had higher levels of proteins that help hold this barrier together, such as ZO-1 and Claudin-3, and more Mucin-2, a protein that helps build protective mucus. Water channels called aquaporins, which move water in and out of the colon, returned closer to normal levels in treated mice.
Finally, the treatment shifted the gut bacteria toward a more balanced mix. The mice showed more types of bacteria, more helpful bacteria, and fewer harmful ones. They also produced more short-chain fatty acids such as butyric acid, which feed the cells lining the colon and support healthy digestion.
The researchers measured several hormones and nerve chemicals that control digestion, including gastrin, motilin, vasoactive intestinal peptide, and acetylcholinesterase. The probiotic brought these levels closer to the healthy range, which may help explain how the gut muscles regained a normal rhythm. Weight gain was also improved in the treated mice, which matters because constipation can reduce appetite and overall well-being in animals.
The team’s correlation analysis linked specific helpful bacteria to higher fatty acid production, lower inflammation, stronger gut lining, and better water handling. This suggests that the bacteria are not just present but may be actively driving the changes. These links are based on patterns in the data, so they point to likely connections rather than proven cause and effect.
Previous research has increasingly connected constipation to the balance of gut bacteria, inflammation, and the health of the intestinal lining. This study fits that picture by showing that a probiotic pair could affect all of these areas together. Earlier probiotic research has often looked at one strain or one outcome, so the combined approach here adds to the case that a multi-part effect is possible. Still, many probiotic studies in mice have not been repeated successfully in people, so the results here should be read in that context.
The most important limitation is that this was an animal study. Mice have digestive systems that differ from ours, and constipation in mice caused by a drug is not the same as long-term constipation in people. The summary also does not state the number of mice in each group, which makes it harder to judge how reliable the results are.
The study also ran for only 21 days, so it does not show whether the benefits last or whether they are safe over many months. It is also unclear whether the same doses or effects would apply to people, and the study did not test human digestion, comfort, or quality of life directly.
The Bottom Line
Based on this early mouse study, the probiotic pair shows promise for constipation, but confidence in its use for people is low at this stage. Those with occasional constipation may wish to discuss probiotics with a healthcare provider, while focusing on proven basics such as fiber, fluids, and physical activity. Confidence should rise only if human trials confirm the effect.
People with ongoing constipation, researchers studying gut health, and companies developing functional foods may find this research relevant. People with serious digestive symptoms such as blood in the stool, sudden changes in bowel habits, severe pain, or unexplained weight loss should see a doctor rather than relying on probiotics. Infants, pregnant people, and those with weakened immune systems should get medical advice before taking any probiotic.
Because the mice were treated for 21 days, the study suggests that changes may appear within a few weeks in an animal model. In people, the timing could be different, and any benefit would likely need several weeks of consistent use to judge. Human research would be needed before anyone can say how long it takes to notice results.
Frequently Asked Questions
Can probiotics help with constipation?
A 2026 mouse study found that a two-strain probiotic mix helped constipated mice pass their first black stool sooner over 21 days. Results in people are not yet known, so anyone with ongoing constipation should talk with a doctor before starting a probiotic.
Which probiotic strains were studied for constipation?
The study tested Lactobacillus acidophilus LA15 and Bifidobacterium animalis subsp. lactis Bi66, combined in equal amounts. The 2026 research was done in male KM mice, so these strains have not yet been proven to work the same way in human digestive systems.
How does a probiotic possibly relieve constipation?
In the mouse study, the probiotic appeared to reduce gut inflammation, strengthen the protective intestinal lining, and increase short-chain fatty acids. It also seemed to help balance gut bacteria and water movement in the colon, though these effects were seen only in animals.
Is a probiotic a safe fix for constipation?
The 2026 study did not report the safety of long-term use in people, and it only lasted 21 days in mice. Probiotic products also vary widely in quality. Anyone with bleeding, severe pain, or sudden bowel changes should see a doctor before trying a supplement.
Want to Apply This Research?
- Log the number of bowel movements per week, the time it takes to pass a stool after taking a probiotic, and a simple stool consistency rating on a 1 to 7 scale such as the Bristol Stool Scale. Record these daily for at least 4 weeks to see a clear pattern.
- Use the app to set a daily reminder to take any probiotic at the same time, and pair it with a daily fiber and water goal. Encourage a short walk after meals, since regular movement supports digestion. Users should check with a doctor before adding a new supplement.
- Track bowel habits, fiber and fluid intake, and any digestive symptoms over several months rather than only a few weeks. Review trends every month and share the logs with a healthcare provider during visits. If symptoms persist, worsen, or include warning signs such as bleeding or severe pain, the app should prompt users to seek medical care.
This article summarizes an early-stage study conducted in mice and does not establish that the probiotic combination is safe or effective for people. It is not medical advice. Anyone with constipation, especially if it is persistent or accompanied by bleeding, severe pain, weight loss, or other concerning symptoms, should consult a qualified healthcare provider before starting any probiotic or making changes to their treatment.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.