Overview
Lactobacillus gasseri is a Gram-positive, rod-shaped, facultatively anaerobic bacterium belonging to the phylum Firmicutes, family Lactobacillaceae. It is a natural inhabitant of the human gastrointestinal tract and vaginal microbiome, and has attracted considerable research attention for its potential role in body weight management and visceral fat reduction. Named after the French microbiologist Francois Gasser, L. gasseri is one of the predominant Lactobacillus species found in the human body and is increasingly recognized as a probiotic of significant clinical interest.
Among the various strains studied, L. gasseri SBT2055 (also known as LG2055) has generated particularly noteworthy data from randomized controlled trials conducted in Japan, demonstrating measurable effects on abdominal adiposity and body composition parameters.
Characteristics
L. gasseri is a homofermentative lactic acid bacterium that produces primarily L-lactic acid through glucose fermentation. It thrives under microaerophilic to anaerobic conditions and grows optimally at temperatures between 33degC and 40degC.
Key features include:
- Morphology: Gram-positive, non-motile, non-spore-forming rods, typically occurring singly or in short chains
- Metabolism: Facultatively anaerobic; primarily homofermentative, producing L(+)-lactic acid
- Habitat: Human gastrointestinal tract (stomach, small intestine, colon), vaginal tract, oral cavity, and breast milk
- Genome: Relatively compact genome (~1.9 Mbp) with genes encoding bile salt hydrolase activity, adhesion factors, and bacteriocin production (gassericin A and T)
- pH tolerance: Survives in the acidic environment of the stomach (pH 2-3), which contributes to its ability to colonize the upper GI tract
Weight Management and Visceral Fat Reduction
The most widely cited clinical evidence for L. gasseri involves its effects on body fat, particularly visceral adiposity. In a landmark randomized, double-blind, placebo-controlled trial, Kadooka et al. (2010) enrolled 87 adults with obese tendencies (BMI 24.2-30.7) and administered fermented milk containing L. gasseri SBT2055 at a dose of approximately 10^8 to 10^9 CFU per day for 12 weeks.[1]
The results showed statistically significant reductions in several body composition parameters compared to placebo:
- Visceral fat area: Decreased by 4.6% (approximately 5.8 cm^2)
- Subcutaneous fat area: Decreased by 3.3%
- Body weight: Decreased by 1.4%
- BMI: Decreased by 1.5%
- Waist circumference: Decreased by 1.8%
A follow-up dose-response trial confirmed these findings, demonstrating that the fat-reducing effects were dose-dependent and reversible upon cessation of supplementation, suggesting that continuous intake may be necessary for sustained benefit.[2]
The proposed mechanisms for these anti-obesity effects include:
- Reduced dietary fat absorption: L. gasseri SBT2055 may increase fat excretion by enlarging fat emulsion droplet size in the intestinal lumen, thereby reducing lipase accessibility
- Modulation of gene expression: Downregulation of genes involved in lipogenesis and upregulation of fatty acid oxidation pathways in adipose tissue
- Inflammation reduction: Suppression of low-grade systemic inflammation associated with adiposity
Additional studies with the BNR17 strain have shown trends toward reduced waist and hip circumference in overweight Korean adults, though some endpoints did not reach statistical significance.[3] These findings underscore that while the evidence is promising, results may be strain-specific and should be interpreted within the context of overall dietary and lifestyle factors.
Vaginal Health and Microbial Defense
L. gasseri is one of the four dominant Lactobacillus species found in the healthy vaginal microbiome, alongside L. crispatus, L. iners, and L. jensenii.[4] Its contributions to vaginal health are mediated through several protective mechanisms:
- Hydrogen peroxide production: L. gasseri produces H2O2, which creates an inhospitable environment for pathogenic organisms such as Gardnerella vaginalis, Prevotella bivia, and other bacteria associated with bacterial vaginosis (BV).[5]
- Lactic acid secretion: The production of lactic acid maintains the vaginal pH at approximately 3.5-4.5, a critical factor in preventing overgrowth of opportunistic and pathogenic microorganisms
- Bacteriocin production: L. gasseri produces gassericin A and gassericin T, antimicrobial peptides with activity against a range of Gram-positive pathogens
- Competitive exclusion: By adhering to vaginal epithelial cells, L. gasseri physically occupies receptor sites that might otherwise be colonized by pathogenic species
Women with vaginal microbiomes dominated by L. gasseri (classified as Community State Type II) generally exhibit lower rates of bacterial vaginosis and sexually transmitted infections compared to women with non-Lactobacillus-dominant communities, though L. crispatus dominance (CST I) is generally considered the most protective profile.
Helicobacter pylori Suppression
L. gasseri has demonstrated the ability to suppress H. pylori, the bacterium responsible for gastric ulcers and a recognized risk factor for gastric cancer. In a clinical study, Sakamoto et al. (2001) found that regular consumption of yogurt containing L. gasseri OLL 2716 (LG21) for 8 weeks significantly reduced H. pylori density in the stomach, as measured by the urea breath test (UBT) delta values.[6]
The anti-H. pylori mechanisms may include:
- Direct antagonism: Production of lactic acid and bacteriocins that inhibit H. pylori growth
- Competitive adhesion: L. gasseri can adhere to gastric epithelial cells, potentially displacing H. pylori from its mucosal niche
- Immune modulation: Enhancement of local mucosal immune responses that help control H. pylori colonization
It is important to note that while L. gasseri supplementation may reduce H. pylori burden, it is not considered a standalone replacement for standard triple or quadruple antibiotic eradication therapy. Rather, probiotic supplementation may serve as an adjunct to conventional treatment, potentially improving eradication rates and reducing antibiotic-associated side effects.
Additional Health Associations
Beyond the primary areas discussed above, preliminary research suggests L. gasseri may play roles in:
- Immune modulation: Enhancement of natural killer (NK) cell activity and modulation of cytokine profiles, potentially supporting innate immune defense
- Oral health: As a resident of the oral microbiome, certain strains may contribute to the balance of oral microbial communities
- Cholesterol metabolism: Some in vitro and animal studies suggest bile salt hydrolase activity that could influence cholesterol levels, though human data remain limited
Safety Profile
L. gasseri has a long history of safe human consumption and is found naturally in fermented dairy products and the human microbiome. It holds Generally Recognized as Safe (GRAS) status in the United States and Qualified Presumption of Safety (QPS) status in Europe. Adverse events in clinical trials have been minimal and comparable to placebo groups. However, as with all probiotics, individuals who are immunocompromised or critically ill should consult a healthcare provider before supplementation.
Key Takeaways
- L. gasseri is a naturally occurring human commensal bacterium found in the gut, vaginal tract, and oral cavity
- The SBT2055 strain has demonstrated statistically significant reductions in visceral fat in Japanese RCTs, though effects are modest and may require continuous intake
- L. gasseri contributes to vaginal health through H2O2 production, lactic acid secretion, and bacteriocin activity
- The LG21 strain has shown ability to suppress H. pylori colonization density in the stomach
- Weight management effects may be strain-specific, and results from Asian populations may not be directly generalizable to all demographics
- L. gasseri supplementation should be viewed as complementary to, not a replacement for, established medical treatments and healthy lifestyle practices