Benefits
Body fat mass in adults with a higher body mass index
In a 12-week placebo-controlled trial in 100 adults in Korea with a BMI of 25 to under 30, 5 billion CFU a day lowered body fat mass, one of two primary measures, versus placebo; body fat percentage did not differ. In a Japanese trial with body composition as the primary outcome, about 50 billion CFU a day lowered fat mass, but not fat percentage or weight, in adults mostly under diabetes care. Both trials were company-linked.
Visceral fat and body fat percentage in adults with a higher BMI
In 80 healthy adults in Japan with a BMI of 25 to under 30, 20 billion CFU a day for 12 weeks did not change visceral fat area, the primary outcome, compared with placebo; it rose on placebo only at weeks 4 and 8. Body fat mass and percent body fat, secondary outcomes, were lower than on placebo at weeks 8 and 12. Six of seven authors work for the maker.
Memory test scores in older adults (studied as MCC1274 and A1)
MCC1274 and A1 are other names for B-3. In a 16-week placebo-controlled trial in 80 older adults with suspected mild cognitive impairment, 20 billion CFU a day raised a memory and thinking test score more than placebo. Two other placebo-controlled trials of the strain, in 121 and 130 older adults, did not meet their main outcome. The maker funded the positive trial and employs most of its authors.
Liver enzyme and inflammation blood markers
In adults with a higher BMI, most under clinical care for diabetes, about 50 billion CFU a day for 12 weeks lowered gamma-glutamyl transferase, a liver enzyme, and high-sensitivity C-reactive protein, an inflammation marker, compared with placebo. In healthy adults given 20 billion CFU a day, no blood marker, including C-reactive protein, differed from placebo.
Leg strength and muscle mass in older adults (heat-killed form)
In a 24-week placebo-controlled trial in 49 adults aged 50 to 89 with age-related muscle loss, heat-killed B-3 at 20 billion cells a day did not improve knee extension strength, the primary outcome. Muscle mass by bioimpedance differed only in unadjusted extra analyses, mostly because it fell on placebo, and DXA scans did not confirm it. The maker funded the trial.
Results from blends that contain the strain
In 100 adults, B. longum BB536 plus this strain (as MCC1274) for 16 weeks lowered visceral fat area compared with placebo. In 38 older adults doing resistance training, a four-strain blend including B-3 did not clearly beat placebo on an attention task. Both trials were maker-linked, and their results belong to the blends, not to B-3 alone.
Mechanism of action
Less fat gain and shifts in liver genes in mice (animal work)
In mice on a high-fat diet, B-3 at 100 million or 1 billion CFU a day for 8 weeks reduced weight and fat gain in a dose-dependent way, improved blood cholesterol, glucose and insulin, raised gut bifidobacteria and shifted fat metabolism genes in the gut, fat tissue and liver. These maker-run mouse results have not been shown to explain the human findings.
Tighter junctions between gut lining cells (lab work)
In human intestinal cells grown in the lab, fluid in which B-3 had grown raised electrical resistance across the cell layer, a sign of tighter seals between cells, and raised the junction protein claudin-4. Acetic acid made by the strain explained part of the effect. This has not been tested in people.
Muscle signaling with heat-killed cells in rodents (animal work)
In rats given heat-killed B-3 for 4 weeks, one leg muscle was heavier and markers of muscle growth and energy production rose, and mice had higher grip strength. A 24-week human trial of the heat-killed form did not find better leg strength.
Clinical trials
Randomized, double-blind, placebo-controlled trial (KCT0006857); 5 billion CFU a day of B-3 (the same raw material as a Morinaga commercial product) or placebo for 12 weeks; the primary endpoint was the change in DEXA body fat mass and body fat percentage, analyzed per protocol; funded by Daehan Chemtech, which employs one author, with two authors from RnBS Corp (Sung et al. 2022, Nutrients)
100 adults in Korea aged 19 to 60 with a BMI of 25 to under 30 (51 B-3, 49 placebo); 83 completed and were analyzed.
Body fat mass, one of the two primary measures, fell more than on placebo at 12 weeks (p = 0.017), while body fat percentage, the other, did not differ (p = 0.376). Waist and hip circumference fell from baseline; the abstract reports them lower than on placebo. Adverse reactions were similar in both groups and none were serious. A published comment questioned whether the fat mass gap exceeded scan error and asked for an intention-to-treat analysis; the authors replied.
Randomized, double-blind, placebo-controlled trial (UMIN000023919); 20 billion CFU a day of B-3 or placebo capsules for 12 weeks; the stated primary outcome was the change in abdominal visceral fat area at week 12; six of seven authors list Morinaga Milk Industry affiliations, and a contract research organization supported the trial (Minami et al. 2018, Biosci Microbiota Food Health)
80 healthy adults in Japan aged 20 to 64 with a BMI of 25 to under 30 (74 men, 6 women); all completed.
Visceral fat area, the primary outcome, rose at weeks 4 and 8 on placebo only, and the authors report no significant difference between groups for it at week 12. Body fat mass and percent body fat, secondary outcomes, were lower than on placebo at weeks 8 and 12 (about 0.6 kg and 0.7 percentage points). Blood lipids did not differ between groups, and BMI did not change. No serious adverse effects were noted.
Randomized, double-blind, placebo-controlled trial after a 4-week run-in; about 50 billion CFU a day of B-3 or placebo for 12 weeks; body composition was the primary outcome; most participants were recruited at a clinic and were under care for diabetes, many taking diabetes drugs; no registration is reported; the paper states there was no funding, and six of ten authors list Morinaga Milk Industry affiliations (Minami et al. 2015, J Nutr Sci)
52 adults in Japan aged 40 to 69 with a BMI of 24 to 30 and a tendency toward obesity, most of them under clinical care for diabetes; 44 analyzed (19 B-3, 25 placebo).
Fat mass was lower in the B-3 group than on placebo at week 12 (p = 0.046), while body fat percentage (p = 0.066) and body weight did not differ. Gamma-glutamyl transferase (p = 0.011) and high-sensitivity C-reactive protein (p = 0.039) improved versus placebo. Because most participants were being treated for diabetes, the result may not apply to healthy adults.
Randomized, double-blind, placebo-controlled trial; 20 billion CFU a day of MCC1274 (A1), a name the maker's FDA filing gives for B-3, or placebo for 16 weeks; the stated primary endpoint was the RBANS total score and the secondary the JMCIS score; funded by Morinaga Milk Industry, which employs six of nine authors; a correction notice was published in 2026 (Xiao et al. 2020, J Alzheimers Dis)
80 physically healthy older adults in Japan with suspected mild cognitive impairment; 79 completed.
The RBANS total score, the primary outcome, improved more than on placebo after 16 weeks (mean between-group difference 11.3 points), with gains in immediate memory, delayed memory and visuospatial domains. The JMCIS score improved versus placebo in the per-protocol analysis (p = 0.036) but not clearly in the intention-to-treat analysis (p = 0.052). No adverse events were observed.
Randomized, double-blind, placebo-controlled trial of B. breve A1 capsules, a name the maker's FDA filing gives for B-3, for 12 weeks, assessed with the Japanese RBANS and the MMSE; all four authors list Morinaga Milk Industry or a clinic affiliation, three of them Morinaga (Kobayashi et al. 2019, Benef Microbes)
121 older adults in Japan with self-reported forgetfulness; 117 completed.
Test scores rose in both groups, and the change from baseline did not differ between A1 and placebo. In a subgroup with low baseline RBANS scores, one RBANS subscale and the MMSE total favored A1, a subgroup result. Blood parameters did not differ, and no adverse effects from A1 were seen.
Randomized, double-blind, placebo-controlled trial; 20 billion CFU a day of MCC1274, a name the maker's FDA filing gives for B-3, or placebo for 24 weeks; ADAS-Jcog was the primary outcome and MMSE the secondary, with MRI and gut bacteria measures; funded by a JSPS KAKENHI grant; Morinaga Milk Industry supplied the product and employs four authors (Asaoka et al. 2022, J Alzheimers Dis)
130 adults in Japan aged 65 to 88 with suspected MCI; 115 in the full analysis set.
The ADAS-Jcog total score, the primary outcome, and the MMSE total score did not differ between groups. The ADAS-Jcog orientation subscale improved more than on placebo at 24 weeks, and two MMSE subscales did so in a subgroup with lower baseline scores. On MRI, a whole-brain gray matter atrophy score, a secondary measure, rose on placebo but not on MCC1274, a significant between-group difference (p = 0.013); atrophy scores for the memory-related brain region did not differ. No adverse events related to the product were observed.
Randomized, double-blind, placebo-controlled pilot trial (jRCTs031200200); heat-killed B-3 at 20 billion cells a day or placebo for 24 weeks; the primary outcome was the change in knee extension strength at week 24, and secondary outcomes were exploratory without adjustment for multiple comparisons; Morinaga Milk Industry funded the trial, supplied the product and employs five of twelve authors (Asaoka et al. 2026, Nutrients)
50 adults in Japan aged 50 to 89 with sarcopenia by AWGS 2019 criteria, a disease population, randomized against a planned 100; 49 analyzed.
Knee extension strength, the primary outcome, did not improve versus placebo. Bioimpedance muscle mass, limb muscle mass, a swallowing questionnaire, IGF-1 and vitamin D favored the product in exploratory analyses, mostly because they declined on placebo, and DXA and physical function measures did not confirm them. Gut bacteria did not differ. No serious adverse events occurred; platelet counts fell slightly within the normal range.