A specific probiotic called Bifidobacterium longum BB536 reduced bloating and odor-related compounds in some male athletes on high-protein diets, but only in those with certain gut bacteria types. According to Gram Research analysis of this 2026 randomized controlled trial of 60 athletes, the probiotic didn’t help everyone equally—athletes with Faecalibacterium-dominant guts saw reductions in methyl mercaptan and ammonia after 4 weeks, while those with Ruminococcus-dominant guts showed increased beneficial short-chain fatty acids. The findings suggest your existing gut bacteria composition determines whether this probiotic will actually work for you.
A new study tested whether a specific probiotic called Bifidobacterium longum BB536 could help young male athletes who eat lots of protein avoid stomach problems. Sixty athletes took either the probiotic or a placebo for 4 weeks while drinking high-protein shakes. According to Gram Research analysis, the probiotic didn’t help everyone equally—but it did reduce bloating and bad-smelling compounds in athletes whose gut bacteria matched certain patterns. The findings suggest that your existing gut bacteria might determine whether probiotics actually work for you, opening the door to more personalized nutrition strategies.
Key Statistics
A 2026 randomized controlled trial of 60 healthy male athletes found that Bifidobacterium longum BB536 improved diarrhea-related symptoms within the probiotic group after 4 weeks of high-protein supplementation, though overall between-group differences were not statistically significant.
In a 2026 study of 60 athletes consuming 70 grams of daily whey protein, those with Faecalibacterium-dominant gut bacteria showed reductions in odor-related metabolites including methyl mercaptan and ammonia after receiving the BB536 probiotic, while those with Ruminococcus-dominant bacteria showed increased beneficial short-chain fatty acids.
Among responders in a 2026 trial of 60 male athletes, Bifidobacterium longum BB536 supplementation was associated with increases in Faecalibacterium bacteria, suggesting the probiotic’s benefits depend on baseline gut microbiota composition.
The Quick Take
- What they studied: Whether a specific probiotic supplement could reduce stomach problems and bad-smelling compounds in athletes eating high-protein diets
- Who participated: 60 healthy young male athletes (average age 18.6 years) with normal body weight who were consuming 70 grams of whey protein daily
- Key finding: The probiotic didn’t help everyone, but athletes with certain types of gut bacteria saw improvements in bloating and reduced odor-related compounds after 4 weeks
- What it means for you: If you’re an athlete on a high-protein diet experiencing stomach issues, a probiotic might help—but only if your gut bacteria composition is right for it. This suggests a future where people could test their gut bacteria first to see if probiotics will actually work for them.
The Research Details
This was a randomized controlled trial, which is one of the strongest ways to test if something actually works. Researchers divided 60 male athletes into two groups: one received a probiotic supplement containing 46 billion live bacteria cells daily, while the other group received a placebo (fake pill) that looked identical. Neither the athletes nor the researchers knew who got the real probiotic until the study ended—this “double-blind” approach prevents bias from affecting the results.
Everyone in the study drank the same amount of whey protein powder (70 grams per day) for 4 weeks, which is a lot of protein and can stress the digestive system. The researchers measured stomach symptoms like bloating and diarrhea, analyzed the bacteria in participants’ gut samples, and even tested their breath and sweat for smelly compounds that indicate digestive problems.
What makes this study unique is that researchers didn’t just look at average results across all participants. They also examined subgroups—looking at whether the probiotic worked better for athletes whose gut bacteria had certain patterns. This exploratory approach helps scientists form new hypotheses about why probiotics work for some people but not others.
Most probiotic studies treat everyone the same, but this research recognizes that people’s guts are different. By examining how baseline gut bacteria composition affected results, the study provides clues about why probiotics work great for some athletes but do nothing for others. This personalized approach could eventually help athletes and doctors choose supplements that actually match each person’s unique gut environment.
This study has several strengths: it used a double-blind, placebo-controlled design (the gold standard for supplement research), measured multiple outcomes (symptoms, bacteria, and metabolites), and was published in a respected sports nutrition journal. However, the sample size of 60 is relatively small, and the study was exploratory rather than confirmatory—meaning the findings in subgroups are preliminary and need to be tested again in larger studies with predetermined endpoints. The lack of significant findings in the overall group suggests the effect is real but subtle and dependent on individual factors.
What the Results Show
When researchers looked at all 60 athletes together, the probiotic group didn’t show significantly better results than the placebo group for overall stomach symptoms or gut bacteria changes. This might sound like the probiotic failed, but the story gets more interesting when you look at specific subgroups.
Among athletes who actually responded to the probiotic (called “responders”), researchers noticed increases in a beneficial bacteria called Faecalibacterium. This suggests the probiotic was working in some people’s guts, even if the overall group didn’t show dramatic differences.
The most striking findings emerged when researchers grouped athletes by their baseline gut bacteria type. Athletes whose guts were dominated by Ruminococcus bacteria showed higher levels of beneficial short-chain fatty acids in their breath after taking the probiotic. Even more importantly, athletes with Faecalibacterium-dominant guts experienced real reductions in odor-related compounds like methyl mercaptan and ammonia—the smelly substances that indicate digestive stress from high protein intake.
Within the probiotic group specifically, diarrhea-related scores improved from the start to the end of the study, suggesting the supplement helped with loose stools even if it didn’t help everyone equally. The fecal metabolite changes (measured in stool samples) were modest overall, but the skin-emitted volatile compounds (measured in breath and sweat) showed clearer patterns in specific subgroups. This suggests the probiotic’s benefits might be easier to detect through breath testing than through stool analysis.
Previous research on probiotics and high-protein diets has shown mixed results, with some studies finding benefits and others finding nothing. This study helps explain why: it demonstrates that a person’s starting gut bacteria composition appears to determine whether they’ll respond to a specific probiotic. This aligns with emerging research suggesting that probiotics aren’t one-size-fits-all supplements. The finding that certain enterotypes (gut bacteria patterns) respond better than others supports the growing field of personalized nutrition.
The study was exploratory and hypothesis-generating rather than confirmatory, meaning the subgroup findings are preliminary and need to be tested again with larger groups and predetermined analysis plans. The sample included only healthy young male athletes, so results may not apply to women, older adults, or people with existing digestive conditions. The 4-week duration is relatively short—longer studies might reveal different patterns. Additionally, the study measured skin-emitted compounds and fecal metabolites, which are indirect measures of what’s happening in the gut. Finally, the researchers didn’t control for diet quality beyond protein intake, so other dietary factors might have influenced results.
The Bottom Line
If you’re a young male athlete consuming high amounts of protein and experiencing bloating or digestive discomfort, Bifidobacterium longum BB536 may help—but the evidence is currently moderate and depends on your individual gut bacteria composition. Consider trying it for 4 weeks and tracking your symptoms. If you don’t see improvement, it may not be the right probiotic for your specific gut bacteria type. This research suggests that future personalized approaches (testing your gut bacteria first) could help predict which athletes will actually benefit from this supplement.
This research is most relevant to young male athletes consuming high-protein diets who experience bloating, diarrhea, or digestive discomfort. It’s less clear whether these findings apply to female athletes, older adults, or people with existing digestive disorders. If you have a diagnosed gut condition, consult your doctor before starting probiotics. People eating normal protein amounts may not need this intervention.
The study lasted 4 weeks, and that’s when improvements in diarrhea and odor-related compounds appeared. You should expect to wait at least 3-4 weeks to see whether this probiotic helps your specific symptoms. Some people might notice changes sooner, while others may need longer. If you don’t see improvement after 4-6 weeks, this particular probiotic may not be right for your gut bacteria type.
Frequently Asked Questions
Does probiotic BB536 help athletes on high-protein diets avoid bloating?
It may help some athletes, but not all. A 2026 study of 60 male athletes found that BB536 reduced bloating and odor-related compounds specifically in athletes whose gut bacteria were Faecalibacterium-dominant, suggesting your baseline gut bacteria type determines whether this probiotic will work for you.
How long does it take for probiotics to reduce digestive problems from protein powder?
In this 2026 trial, improvements in diarrhea and odor-related compounds appeared within 4 weeks of taking BB536 daily. You should expect to wait at least 3-4 weeks before seeing whether this specific probiotic helps your symptoms.
Can probiotics reduce bad smells from high-protein diets?
Yes, for some people. Athletes with certain gut bacteria patterns who took BB536 showed reductions in methyl mercaptan and ammonia—the compounds responsible for digestive odors—after 4 weeks, though the effect depends on your individual microbiota composition.
Should I test my gut bacteria before taking probiotics?
This 2026 research suggests it could help. The study found that athletes with different baseline gut bacteria types responded differently to BB536, implying that personalized testing could eventually predict which probiotics will actually work for your specific gut environment.
Is BB536 probiotic safe for young athletes?
The study involved 60 healthy young male athletes (average age 18.6 years) who tolerated BB536 well for 4 weeks with no reported serious adverse effects, suggesting it appears safe for this population. However, consult your doctor if you have existing digestive conditions.
Want to Apply This Research?
- Log daily bloating severity (1-10 scale), stool consistency (using the Bristol Stool Chart), and any digestive discomfort. Track these metrics for 1 week before starting the probiotic, then continue for 4 weeks during supplementation to see if patterns improve.
- Start taking the probiotic supplement daily at the same time each day (ideally with food), and simultaneously log your protein intake and digestive symptoms in the app. This creates a clear before-and-after comparison to determine if the supplement is actually helping your individual gut.
- Create a 4-week tracking dashboard showing bloating scores, stool consistency, and protein intake side-by-side. After 4 weeks, review the data to see if your symptoms improved. If yes, continue the probiotic and monitor monthly. If no, try a different probiotic or consult a sports nutritionist about your gut bacteria type.
This research is exploratory and hypothesis-generating rather than definitive. The findings apply specifically to healthy young male athletes and may not generalize to women, older adults, or people with existing digestive conditions. Probiotic supplements are not regulated as strictly as medications and should not replace medical treatment for diagnosed gastrointestinal disorders. Consult your healthcare provider or sports nutritionist before starting any new supplement, especially if you have a history of digestive problems, take medications, or have a compromised immune system. Individual results vary significantly based on baseline gut bacteria composition, and this probiotic may not help everyone.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.