Lactobacillus gasseri: The Strain Most Associated With Visceral Fat Research

Lactobacillus gasseri is the probiotic strain that influencers love to call a “weight loss bacteria.” The truth is more nuanced. A small body of peer-reviewed research — concentrated around two sub-strains (SBT2055 and BNR17) — suggests L. gasseri is associated with modest visceral-fat reductions in some trial populations. That is not the same as “burns belly fat,” and it is not a substitute for diet, sleep, or movement. This guide separates the science from the marketing.

Short answer: what L. gasseri does (and doesn’t) do

If you came here because TikTok told you L. gasseri “melts belly fat,” the honest answer: a handful of well-conducted human trials — most prominently Kadooka 2010 using strain SBT2055 in fermented milk — have shown statistically significant but modest reductions in visceral fat in overweight adults consuming clinical doses for 12 weeks. The mean reduction was on the order of 4–5% of visceral fat area, not the dramatic weight changes implied by influencer marketing.

That said, L. gasseri is a legitimate human-origin probiotic species with documented roles in the digestive tract, the vaginal microbiome, and infant gut development. The problem is the gap between what the trials measured (a specific strain, dose, and population) and what the supplement industry implies (any “gasseri” product helps you lose weight). We’ll keep the evidence and the marketing narrative separate.

What Lactobacillus gasseri actually is

Lactobacillus gasseri is a Gram-positive, rod-shaped lactic acid bacterium named after German microbiologist Francois Gasser, who characterized it in the 1970s. Unlike some probiotic species that originated in dairy fermentation, L. gasseri is a true human-origin commensal — part of the natural microbial community in the digestive tract, the vaginal canal, and breast milk.

Like other Lactobacillus species, it ferments sugars into lactic acid, lowering local pH and creating an environment less hospitable to opportunistic microbes. In the gut, it contributes to general microbial balance. In the vaginal canal, it helps maintain the protective acidic pH. In infant gut development, it is one of the first species seeded via breast milk. Its closest taxonomic relatives are L. johnsonii and L. crispatus.

Where L. gasseri is found in the body

One of the reasons L. gasseri is interesting is that it occupies multiple body sites, and its role differs in each:

• Human GI tract — L. gasseri is part of the small-intestine and upper-colon microbial community in most healthy adults. Population studies suggest it is more abundant in some geographic regions (notably East Asian populations) than others, which becomes relevant when interpreting trial data done in Japan and Korea.
• Vaginal microbiome — alongside L. crispatus, L. iners, and L. jensenii, L. gasseri is one of the dominant species in the protective vaginal microbiome of reproductive-age women. Vaginal-microbiome research has examined its role in maintaining acidic pH and reducing susceptibility to bacterial vaginosis and yeast overgrowth.
• Breast milk — L. gasseri is consistently isolated in human breast milk, transferred from mother to infant, and contributes to the establishment of the early gut microbiome. This is partly why some women’s and infant probiotic formulas include it.

That tri-site distribution is why L. gasseri shows up in three different supplement categories: general gut formulas, women’s health and vaginal probiotics, and weight-management products. The species is the same; the marketing context is different. For a broader view of how strains divide labor in the body, see our gut health glossary.

The two sub-strains that matter: SBT2055 and BNR17

Here is the most important thing to know about L. gasseri research: almost all of the visceral-fat data is from two specific sub-strains, not the species at large. If a label simply says “L. gasseri” without a strain code, you have no way to know whether the lineage in the capsule matches the lineage in the trials.

• SBT2055 (also written LG2055) — a strain isolated by Snow Brand Milk Products (now Megmilk Snow Brand) in Japan. SBT2055 is the strain used in the Kadooka 2010 trial published in the European Journal of Clinical Nutrition, which is the most-cited L. gasseri paper in the visceral-fat literature. Subsequent Japanese trials have used the same strain in fermented milk and capsule formats.
• BNR17 — a strain isolated from human breast milk and developed in South Korea. BNR17 has been studied in several Korean clinical trials, including a 2018 randomized controlled trial published in the Journal of Medicinal Food that examined its effects on body weight and waist circumference in overweight Korean adults.

Two other strains — OLL2716 (a Meiji strain studied for H. pylori support, not weight) and CECT5714 (Spanish-isolated, studied in vaginal-health contexts) — round out the better-documented L. gasseri lineages, but neither has the visceral-fat dataset of SBT2055 or BNR17.

Bottom line: when someone says “L. gasseri is studied for weight,” the honest version is “two sub-strains of L. gasseri, at clinical doses, in specific populations, have shown modest visceral-fat reductions.”

What the peer-reviewed evidence actually shows

Let’s walk through the trials that actually generated the “L. gasseri for weight” narrative, and what they found in plain English.

Kadooka et al. 2010 (European Journal of Clinical Nutrition) — the foundational paper. A 12-week, double-blind, randomized, placebo-controlled trial in 87 Japanese adults with elevated BMI and abdominal adiposity. The intervention group consumed fermented milk containing 5 × 10¹⁰ CFU of L. gasseri SBT2055 per day. At 12 weeks, the SBT2055 group showed a 4.6% reduction in visceral fat area, a 1.4% reduction in body weight, and modest reductions in waist circumference compared to the placebo group. These were statistically significant but modest in magnitude. The effect was associated with reduced visceral fat specifically, not dramatic overall weight loss.

Kim et al. 2018 (Journal of Medicinal Food) — the BNR17 trial. A 12-week, double-blind, randomized, placebo-controlled trial in 90 overweight Korean adults. The intervention group received L. gasseri BNR17 capsules at 10¹⁰ CFU per day. The BNR17 group showed reductions in waist and hip circumference compared to placebo. Body weight changes were modest. The mechanism proposed in the paper involves bacterial influence on fat absorption and adipocyte signaling, though the precise pathway is not fully established.

Jung et al. 2013 — a Korean trial in women examined L. gasseri BNR17 for general GI symptoms and metabolic markers, with secondary findings related to body composition. The trial supports BNR17’s safety and tolerability in adult women.

Itoh et al. 2011 — a separate line of research examining L. gasseri’s role in endometriosis-related pelvic pain. This study used strain OLL2809 and reported reduced menstrual pain scores in women with endometriosis — an entirely separate use case from visceral fat.

Million et al. 2012 — a meta-analysis on Lactobacillus species and obesity. The paper notes that the relationship between Lactobacillus species and body weight is species- and strain-dependent: some species (including specific L. gasseri strains) are associated with leanness in observational data; others are not.

How much, how long, and what form

If you decide to try L. gasseri, here are the parameters used in the trials so you can compare them to what’s on a label:

• Dose — the Kadooka SBT2055 trial used 5 × 10¹⁰ (50 billion) CFU per day. The Kim BNR17 trial used 10¹⁰ (10 billion) CFU per day. Most consumer L. gasseri capsules deliver 1–20 billion CFU per serving, often well below the SBT2055 trial dose.
• Duration — both major trials ran for 12 weeks. Effects were observed by the 12-week mark; shorter periods may not produce measurable changes. This is not a one-week intervention.
• Form — the original Kadooka trial used fermented milk as the delivery vehicle. The BNR17 trial used capsules. Either can deliver live bacteria; what matters is CFU at expiration, not at manufacture, and whether the strain matches the trial strain.
• Timing — with or just before a meal, daily, at a consistent time. Food buffers stomach acid and improves the survival rate of live bacteria through the upper digestive tract.
• Realistic expectations — if the trial effects translate to an individual user (and that is an “if”), expect a small reduction in visceral fat over 12 weeks alongside an otherwise unchanged diet. The effect is additive to, not a replacement for, dietary and lifestyle changes.

For a broader discussion of supplements marketed for body composition, see our guide to the best probiotic for weight loss, which puts L. gasseri in context with other strains and with the limits of probiotic research in this category.

Safety and who should avoid it

L. gasseri has a strong safety profile as a human-origin commensal with a long history of consumption in fermented dairy. Both SBT2055 and BNR17 have completed standard safety evaluations in their trial programs without significant adverse-event signals at the doses used. Mild, transient digestive symptoms (gas, mild bloating, stool changes) can occur in the first 1–2 weeks of any new probiotic.

Populations who should consult a clinician before starting any probiotic include those with severe immunosuppression, central venous catheters, recent major surgery, severe acute pancreatitis, or critical illness. Pregnant women should choose probiotics labeled for pregnancy and consult their obstetric provider. Children should use age-specific formulas.

L. gasseri vs. other strains marketed for weight

L. gasseri is not the only probiotic species marketed for weight or metabolic health, and it’s worth understanding where the evidence sits across the category:

• L. gasseri (SBT2055, BNR17) — modest visceral fat reduction in 12-week trials, mostly East Asian populations. The strain with the most specific visceral-fat dataset.
• Bifidobacterium lactis (B420) — a Finnish trial published in EBioMedicine in 2019 examined B420 in overweight adults and reported modest reductions in body fat mass over 6 months. Effect size comparable to L. gasseri.
• L. plantarum (Lp-115, others) — some metabolic-marker data, weaker dataset specifically for body fat.
• L. rhamnosus (LPR) — a Canadian trial in women examined LPR and reported body-composition changes in women specifically (not men), in a single, modest-sized trial. See our Lactobacillus rhamnosus guide for the broader research base.
• Akkermansia muciniphila — a newer category with small early trials and growing interest, but the consumer-supplement category is still in its early days.

The honest read across the field: probiotics in the weight-management space produce small, statistically significant effects in some trials, with strain- and population-dependent variability. None of them are a replacement for nutrition, sleep, and physical activity. They are, at best, an additive layer of support for a person already doing the foundational things.

Who might reasonably consider L. gasseri

Given the actual evidence, here are the people for whom L. gasseri is a more reasonable consideration:

• Adults with elevated visceral adiposity who are already doing the lifestyle work (a structured nutrition pattern, adequate sleep, regular movement) and want an additive layer of support over 12 weeks.
• Women interested in vaginal-microbiome support, particularly in the context of recurrent dysbiosis or yeast overgrowth, where L. gasseri is one of several species (alongside L. crispatus) studied in this area. Our best probiotic for women guide covers women’s formulas in more depth.
• Women with endometriosis-related pelvic pain who are exploring the gut-pelvic-pain axis. The Itoh OLL2809 line of research is small but interesting; see our endometriosis and gut health guide.
• People who have already optimized their daily probiotic foundation and are looking to layer a specific, targeted strain on top.

Who probably shouldn’t expect much: people who haven’t addressed their diet, sleep, or movement; people expecting dramatic weight loss; people taking a generic “L. gasseri” product without a documented strain designation.

The bottom line

Lactobacillus gasseri is a real, well-characterized, human-origin probiotic species with three legitimate research contexts: visceral fat in two sub-strains, vaginal microbiome support, and endometriosis-related pelvic pain in one strain. It is not a weight-loss treatment, the visceral-fat effect is modest, and the strain matters more than the species name on the label. Used with honest expectations — clinical strain, clinical dose, 12 weeks, alongside diet and lifestyle work — it has a defensible place in a thoughtful supplement stack. Used as a shortcut around the foundational drivers of body composition, it will disappoint. A probiotic, including L. gasseri, is an additive layer on the foundation of real food, sleep, movement, and stress management — not a substitute for it.