Human Bifidobacterium BB536 Suggests Improvement in Diarrhea-Related QOL Scores and Reduction of Body Odor-Related Metabolites in Male Athletes Consuming a High-Protein Diet

Joint research conducted by Professor Shuichi Machida of Juntendo University Graduate School of Health and Sports Science, Professor Daisuke Asaoka of Juntendo Tokyo Koto Geriatric Medical Center, and Morinaga Milk Industry Co., Ltd. investigated the effects of ingesting *Bifidobacterium longum* BB536, a human-resident *Bifidobacterium* species, in male athletes consuming a high-protein diet. The results suggested potential improvements in diarrhea-related Quality of Life (QOL) scores and a reduction in body odor-related metabolites. These research findings were published in the scientific journal 'Journal of the International Society of Sports Nutrition' on April 28, 2026.

**Key Points of This Research**

* Ingestion of *Bifidobacterium* BB536 showed a trend towards improvement in diarrhea-related QOL scores. * In subjects whose diarrhea-related QOL scores improved, the occupancy rate of the butyrate-producing bacterium *Faecalibacterium* in the gut microbiota increased. * The effect of *Bifidobacterium* BB536 on "body odor-related metabolites" is suggested to depend on the gut bacterial type (enterotype*1). * In some enterotypes, an effect of reducing body odor-related metabolites in athletes consuming a high-protein diet was suggested.

**1. Background of the Study**

Athletes often consume high-protein diets for muscle recovery and growth. However, excessive intake can lead to concerns about disruption of the gut environment, digestive symptoms, and an increase in metabolites that cause body odor. While probiotics are known for their gut environment improving effects, research targeting athletes consuming high-protein diets has been limited. Therefore, Morinaga Milk, which has been researching *Bifidobacterium* BB536 for over 50 years, conducted an exploratory study to investigate its effects.

**2. Research Methods**

A randomized, double-blind, placebo-controlled, parallel-group comparative study was conducted on 60 healthy male athletes belonging to Juntendo University's athletic club. Participants ingested either capsules containing *Bifidobacterium* BB536 or placebo capsules for 4 weeks. Both groups also concurrently consumed 70g/day of whey protein. Digestive symptoms (Izumo scale*2), gut microbiota (16S rRNA analysis), and body odor-related metabolites (skin gas*3 measurement) were evaluated.

**3. Research Results**

**① On digestive symptoms: Ingestion of *Bifidobacterium* BB536 showed a trend towards improvement in diarrhea-related QOL scores.**

Although no inter-group difference was confirmed between the *Bifidobacterium* BB536 intake group and the placebo intake group, the *Bifidobacterium* BB536 intake group showed a significant improvement in diarrhea-related QOL scores after 4 weeks of intake (Figure 1).

Figure 1: Changes in diarrhea-related QOL scores

Diarrhea-related QOL scores were calculated as the sum of 3 items related to diarrhea symptoms on the Izumo scale (0-15 points).

(BB536 group: n = 29, Placebo group: n = 30)

(*: p < 0.05 indicates statistical significance by Wilcoxon signed-rank test)

**② On gut microbiota: In subjects with improved diarrhea-related QOL scores, the occupancy rate of the butyrate-producing bacterium *Faecalibacterium* in the gut microbiota increased.**

In subjects whose diarrhea-related QOL scores improved (responders), the gut bacterial occupancy rate of *Faecalibacterium*, a butyrate-producing bacterium with anti-inflammatory effects, significantly increased after 4 weeks of *Bifidobacterium* BB536 intake compared to non-responders (Figure 2). This suggests that the improvement effect of *Bifidobacterium* BB536 mentioned in ① may depend on the gut microbiota.

Figure 2: Changes in gut bacterial occupancy rate of butyrate-producing *Faecalibacterium* in responders and non-responders

The BB536 intake group was divided into responders (n = 9) and non-responders (n = 19), and the occupancy rate of intestinal *Faecalibacterium* before and after intake was calculated. (*: q < 0.05 indicates statistical significance considering multiplicity by non-parametric ANCOVA)

**③ The effect of *Bifidobacterium* BB536 on body odor-related metabolites is suggested to depend on the gut bacterial type (enterotype).**

To clarify the effect of *Bifidobacterium* BB536 on body odor-related metabolites based on differences in subjects' gut microbiota, participants were classified into the following two enterotypes based on their gut microbiota before intake:

* R-type: *Ruminococcus*-dominant (*Bifidobacterium* BB536 group: n = 8, Placebo group: n = 10)

* F-type: *Faecalibacterium*-dominant (*Bifidobacterium* BB536 group: n = 21, Placebo group: n = 20)

In both enterotypes, no inter-group difference was confirmed for body odor-related metabolites between the *Bifidobacterium* BB536 intake group and the placebo intake group, but in the R-type, *Bifidobacterium* BB536 showed a trend for reduction in body odor related metabolites after 4 weeks of intake. The full sentence was truncated in the original text, but it is implied there is an effect. The implications will be discussed further.