Human Bifidobacterium BB536 Suggested to Improve Diarrhea-Related QOL Scores and Reduce Body Odor-Related Metabolites in Male Athletes Consuming High-Protein Diets

Morinaga Milk and Professor Shuichi Machida of Juntendo University Graduate School of Health and Sports Science, along with Professor Daisuke Asaoka of Juntendo Tokyo Koto Geriatric Medical Center, conducted a joint study. The research investigated the effects of consuming Bifidobacterium longum BB536, a human-resident Bifidobacterium species, on male athletes who consume high-protein diets. 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:

● Intake of Bifidobacterium BB536 showed a tendency to improve diarrhea-related QOL scores. ● In the gut microbiota of subjects whose diarrhea-related QOL scores improved, the occupancy rate of the butyrate-producing bacterium Faecalibacterium increased. ● The effect of Bifidobacterium BB536 on “body odor-related metabolites” was suggested to depend on the gut bacterial type (enterotype*1). ● In some enterotypes, an effect of reducing body odor-related metabolites in athletes consuming high-protein diets was suggested.

1. Research Background

Athletes often consume high-protein diets for muscle recovery and growth. However, excessive intake raises concerns about gut environment disruption, 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 conducted an exploratory study on the effects of consuming Bifidobacterium BB536, which it has been researching for over 50 years.

2. Research Methods

A randomized, double-blind, placebo-controlled, parallel-group comparison study was conducted on 60 healthy male athletes belonging to Juntendo University's athletic clubs. Participants consumed capsules containing Bifidobacterium BB536 or placebo capsules for 4 weeks, with both groups also taking 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 Regarding digestive symptoms: Intake of Bifidobacterium BB536 showed a tendency to improve diarrhea-related QOL scores.

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

Figure 1: Changes in diarrhea-related QOL scores

Diarrhea-related QOL scores were calculated as the total score 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 Regarding gut microbiota: In the gut microbiota of subjects whose diarrhea-related QOL scores improved, the occupancy rate of the butyrate-producing bacterium Faecalibacterium 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 in ① by Bifidobacterium BB536 may depend on the gut microbiota.

Figure 2: Changes in gut bacterial occupancy rate of butyrate-producing bacterium 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 gut Faecalibacterium before and after intake was calculated. (*: q < 0.05 indicates statistical significance considering multiplicity by non-parametric analysis of covariance)

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

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

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

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

In both enterotypes, although no inter-group difference was confirmed between the Bifidobacterium BB536 intake group and the placebo intake group for body odor-related metabolites, in the R-type, an effect of reducing body odor-related metabolites in athletes consuming high-protein diets was suggested.