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Lactobacillus gasseri (SBT2055, BNR17)
The probiotic sold for belly fat. Two Japanese trials and one Korean trial did report less visceral fat, but the Japanese results are within-group changes from baseline rather than proper comparisons against placebo, the effect faded within four weeks of stopping, another human trial found nothing, and the total weight change is around one kilogram.
What the evidence says
Most L. gasseri studies are mechanism or observational rather than RCTs that measure a clinical effect — keep findings provisional.
Most evidence is from medium-quality meta-analyses and randomised trials published 2010–2026 with a typical study size of 87 participants.
Based on 11 studies · 2 meta-analyses · 5 RCTs · 524 total participants
Confidence
High confidenceBy outcome
A visceral-fat claim resting mostly on within-group changes from baseline in manufacturer-run trials, with roughly one kilogram of weight change, no dose-response, an effect that faded four weeks after stopping, and one null human trial.
3 trials ongoing or recruiting · 11 completed on ClinicalTrials.gov
Registered trials show research momentum for L. gasseri, not proof of effect — a registration is a plan, and posted results are sponsor-reported, not peer-reviewed. They are never counted toward the evidence rating above.
Browse these trials on ClinicalTrials.govClinicalTrials.gov · as of Sep 2026
Under EU law (Reg. 1924/2006), EFSA reviews whether a specific health claim for L. gasseri meets the evidence standard. These are independent regulatory decisions on claims — not studies, and never counted toward the evidence score above.
Not authorised by EFSA
“Lactobacillus gasseri CECT5714 and Lactobacillus coryniformis CECT5711 -probiotic -balances your healthy intestinal flora; -improves your intestinal transit”
“Not authorised” means the specific claim wording did not meet the EU’s evidence standard — often a matter of dossier or phrasing, not proof of no effect. EFSA judges marketing claims and is kept separate from our study-based evidence score.
Source: EU Register of nutrition and health claims (European Commission / EFSA) · register snapshot Feb 2013
Our research database did not respond in time, so the studies and count above cover only our curated set. This refreshes automatically.
Lactobacillus gasseri is marketed almost entirely on a body-fat claim, and the honest summary is that the effect — if real — is small, fragile and unevenly supported. Two strains carry the evidence.
SBT2055 (LG2055), from Snow Brand / Megmilk Snow Brand, produced the original 2010 result: in 87 adults with obese tendencies, abdominal visceral fat fell 4.6% (-5.8 cm²) and body weight 1.1 kg over 12 weeks.
The catch is that these are changes from baseline within the active group; the paper reports that the control group did not change significantly, which is not the same as a statistically significant difference between groups — and high-molecular-weight adiponectin, offered as a mechanism, rose about equally in both arms.
The larger 2013 follow-up (n=210) reported 8.2-8.5% reductions in visceral fat area on the same within-group basis, found no dose-response at all between 10^6 and 10^7 CFU/g, and noted that stopping for four weeks attenuated the effect.
The Korean strain BNR17 supplies the one genuinely between-group result: at 10^10 CFU/day, visceral adipose tissue was 21.6 cm² lower than placebo (P=0.012), though every biochemical parameter was unchanged.
Against that, an earlier BNR17 trial in 62 overweight adults was null — a slight weight reduction with no significant difference between groups — and PubMed does not index it as a randomised controlled trial.
A 2012 meta-analysis of Lactobacillus species did associate L. gasseri with weight loss in obese humans and animals, while noting that L. acidophilus was associated with weight GAIN, which is the more interesting finding for anyone assuming probiotics are uniformly slimming.
Outside body composition, a serum fatty-acid study was a sequential, non-randomised within-subject design without a parallel placebo arm, and a 2026 strain-specific review explicitly failed to find efficacy for BNR17 in irritable bowel syndrome.
The animal work is likewise inconsistent: one mouse study reported reduced body weight and fat, another reported body weight and abdominal fat were NOT altered by the same strain. Treat this as an emerging, manufacturer-heavy literature, not a weight-loss tool.
In a sequential within-subject study in people with high triglycerides, postprandial non-esterified fatty acids from 120-480 minutes and the 120-minute triglyceride level were lower after 4 weeks of the fermented milk containing the strain. That study was single-blind and not randomised, with no parallel placebo group.
In rats, the strain raised carbohydrate oxidation during the active phase and increased energy expenditure, reduced cumulative blood glucose after 3 weeks, and raised the butyrate share of caecal short-chain fatty acids. This mechanism has not been demonstrated in humans.
Diet-induced obese mice showed lower macrophage infiltration into adipose tissue and down-regulated CCL2/CCR2 expression. Notably, in that same study body weight and abdominal fat weight were NOT altered — so the anti-inflammatory signal and the anti-obesity claim came apart.
How L. gasseri works — from molecular targets to health outcomes. Click an edge to see supporting research.This visualization is in beta — pathways are being refined and expanded.
No trial has enrolled pregnant or breastfeeding women. Discuss with a clinician.
Set expectations at roughly 1 kg over 12 weeks, largely from within-group comparisons, reversing after you stop. This is not a substitute for anything that actually works.
A 2026 strain-specific review did not demonstrate efficacy for BNR17 in IBS. Choose a strain with positive strain-level evidence instead.
A general consideration for any live bacterial product — antibiotics can reduce the viable dose. No L. gasseri trial tested concurrent antibiotic use.
Tip: The 12-week trials reported no special or severe adverse reactions in either arm
L. gasseri has an evidence score of 4/10 — emerging evidence based on 15 indexed studies, including 2 meta-analyses. The probiotic sold for belly fat. Two Japanese trials and one Korean trial did report less visceral fat, but the Japanese results are within-group changes from baseline rather than proper comparisons against placebo, the effect faded within four weeks of stopping, another human trial found nothing, and the total weight change is around one kilogram. Representative study: PMID 41682832.
The commonly studied dose of L. gasseri is Trial doses ranged from about 2 x 10^8 CFU/day (fermented milk at 10^6 CFU/g, 200 g/day) up to 10^10 CFU/day (BNR17). The only between-group visceral-fat result came at 10^10 CFU/day; the SBT2055 trials found no difference between their low and intermediate doses.. Individual needs vary — start at the lower end of the range and adjust based on how you respond.
The best time to take L. gasseri is with meals. Take it with food. The SBT2055 trials delivered the strain in 200 g/day of fermented milk consumed as part of the daily diet, and the fatty-acid study measured its effect on a fat-loading meal.
L. gasseri is generally well-tolerated and considered safe for most healthy adults at recommended doses. Reported side effects are uncommon and include mild digestive upset or bloating. Use caution if any of these apply to you: Immunocompromise or critical illness (a general precaution for live bacterial products; no L. gasseri trial enrolled such patients).
VSL#3 / Visbiome
Mostly mechanism / observationalAn 8-strain blend dosed in the hundreds of billions to trillions of CFU per day — roughly 45 to 7,000 times a typical 1-10 billion CFU consumer probiotic — with the largest effect size in the probiotic literature for one narrow use: maintaining remission in chronic pouchitis after ulcerative colitis surgery. It is null for IBS and Crohn's — and since 2016 the brand name no longer reliably identifies the formulation that was studied.
B. lactis (BB-12 / HN019)
Mostly mechanism / observationalThe most-replicated probiotic effect on gut transit — it measurably speeds things up and adds roughly one bowel movement a week in people who are already low. But it is not a constipation cure: the two largest, best-designed trials both missed their primary endpoints, and the honest effect is hours off transit time, not a fix.
L. reuteri DSM 17938
Mostly mechanism / observationalThe best-evidenced probiotic for infant colic — but specifically in breastfed babies, where an individual-participant meta-analysis found a number-needed-to-treat of 2.6. In formula-fed infants the benefit disappears, and the largest single trial actually favoured placebo. Adult claims mostly belong to different L. reuteri strains entirely.
L. rhamnosus GG
Mostly mechanism / observationalOne of the two most-studied probiotic strains, and a case study in why strain-level evidence matters. It has one genuinely strong, guideline-endorsed use — preventing antibiotic-associated diarrhea in children — while its two most-marketed uses, treating stomach bugs and preventing eczema, were both overturned by the largest and best-run trials.
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Reviewed by Dr. Baher Al Hakim · Last reviewed July 2026 · evidence from 11 studies · how we score · editorial policy
This information is for educational purposes only. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement or medication.
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