L. gasseri is a probiotic that recently gained in popularity due to reports of weight loss and decreased blood sugar. Which of its potential benefits are backed up by science? Read on to find out.
What is Lactobacillus gasseri?
Lactobacillus gasseri is a lactic acid bacteria that is being investigated for various potential health benefits because of its antimicrobial activity, bacteriocin production, and purported modulation of the innate and adaptive immune systems .
Potential Benefits of L. gasseri
L. gasseri probiotic supplements have not been approved by the FDA for medical use. Supplements generally lack solid clinical research. Regulations set manufacturing standards for them but don’t guarantee that they’re safe or effective. Speak with your doctor before supplementing.
Possibly Effective For
1) Weight Management
L. gasseri significantly decreased BMI, abdominal visceral fat, waist and hip circumferences, and body fat mass in 210 healthy Japanese adults, with an 8.5% decline in abdominal fat area over twelve weeks. However, the authors warned that constant consumption of this probiotic may be required to maintain this effect .
Despite there being no change in behavior or diet, administration of L. gasseri modestly reduced weight and waist and hip circumference in obese and overweight adults .
L. gasseri significantly decreased body weight and visceral and subcutaneous fat areas in adults with obese tendencies .
L. gasseri reduced body weight and fat tissue mass in mice  and rats .
L. gasseri prevented weight gain in obese mice .
L. gasseri prevented abdominal fat accumulation  and decreases body weight in adults with obese tendencies .
L. gasseri suppressed lipase-mediated fat hydrolysis in humans  and mice .
L. gasseri prevented the enlargement of fat cells and an increase in abdominal fat volume in rats, mice, and humans [10, 11, 12].
L. gasseri inhibited dietary fat absorption in rats .
L. gasseri ameliorated systemic and fat tissue inflammation in obese mice , by inhibiting macrophage invasion .
Heat-killed L. gasseri stimulated respiratory immune responses of obese host animals to enhance their natural defense against respiratory infection .
L. gasseri also significantly reduced leptin concentrations in rats [11, 12, 15].
Insufficient Evidence For
Researchers are currently investigating whether L. gasseri has other health benefits. The potential benefits in this section have produced positive results in at least one clinical trial, but these studies are small, contradictory, or otherwise limited. Talk to your doctor before supplementing with L. gasseri for any reason.
A synbiotic product containing L. gasseri and inulin reduced total blood cholesterol, low-density lipoprotein (LDL)-cholesterol and triglycerides in hypercholesterolemic men and women .
L. gasseri significantly reduced the blood and liver cholesterol in rats [12, 17, 18].
Heat-killed L. gasseri enhanced immunity in the elderly. This probiotic increases the number of CD8(+) T cells and reduces CD28 expression loss in CD8(+) T cells .
Heat-killed L. gasseri increased natural killer cell (NK cell) activities and enhanced cell-mediated immunity in aged host animals, thereby altering age-related immunosenescence .
Live and heat-killed L. gasseri protected mice against the influenza virus and ameliorated infection symptoms, apparently by stimulating local and systemic immune responses [21, 22].
L. gasseri exhibited anti-herpes virus (HSV-2) activity .
4) Gut Health
L. gasseri beneficially modified the microbiota, increasing Bifidobacteria and decreasing Clostridium in human subjects .
Heat-killed L. gasseri accelerated the resolution of symptoms and reduced mortality of enteropathogenic E. coli -infected mice .
L. gasseri increased IgA levels in breast milk and reduces the incidence of diarrhea in mouse pups with rotavirus infection .
Yogurt containing L. gasseri significantly inhibited the formation of gastric ulcers in rats in a dose-dependent manner [27, 28, 29].
L. gasseri suppressed H. pylori and reduced gastric mucosal inflammation in infected patients .
A 4-week treatment with L. gasseri -containing yogurt improved the efficacy of triple therapy in patients with H. pylori infection .
L. gasseri yogurt suppressed dyspeptic symptoms in H. pylori-infected patients .
L. gasseri significantly reduced the rate of both H. pylori and H. suis infections in mice [33, 34].
Heat-killed L. gasseri improved nasal symptoms and pollen-specific IgE levels in subjects with Japanese cedar pollinosis .
L. gasseri enhanced the Th1 immune responses in subjects with perennial allergic rhinitis .
L. gasseri enhanced oral tolerance in allergies in mice, possibly by increasing the ratio of effector regulatory T cells .
Heat-killed L. gasseri suppressed eosinophilia in cedar pollen antigen-challenged mice, by modulating the Th1/Th2 balance .
L. gasseri ingestion prevented the reduction of natural killer (NK) cell activity due to strenuous exercise and elevated mood from a depressed state in university-student athletes .
L. gasseri and αLA alleviated minor resting fatigue in university-student athletes after strenuous exercise .
L. gasseri improved menstrual pain and dysmenorrhea in patients with endometriosis .
L. gasseri inhibited the growth of endometrial tissue in the abdominal cavity in mice and rats .
Animal Research (Lacking Evidence)
No clinical evidence supports the use of L. gasseri probiotics for any of the conditions listed in this section. Below is a summary of the existing animal and cell-based research, which should guide further investigational efforts. However, the studies listed below should not be interpreted as supportive of any health benefit.
8) Glucose Tolerance
L. gasseri increased energy expenditure, reduced blood glucose, improved glucose tolerance, and attenuated inflammation in rats .
It also reduced insulin levels in rats .
L, gasseri decreased blood glucose and improves glucose sensitivity in type 2 diabetic mice .
9) Metabolic Syndrome
L. gasseri decreased food and energy intakes and improved body weight, insulin resistance, and cholesterol levels in rats with metabolic syndrome (MS) .
L. gasseri prevented high-fat-diet-induced inflammation and lowered the ratio of inflammatory-type macrophages to anti-inflammatory ones in fat tissue of mice .
L. gasseri ameliorated systemic and fat tissue inflammation in obese mice [10, 7].
L. gasseri yogurt prevented proliferative and inflammatory changes in the stomach caused by C. albicans in mucosal candidiasis in rats .
L. gasseri attenuated allergen-induced airway inflammation and IL-17 proinflammatory immune response in mice with allergic asthma .
13) Oxalate Degradation
L. gasseri degrades oxalate in laboratory experiments and may be beneficial in managing oxalate kidney stone disease .
Mechanism of Effect
Researchers have conducted a number of cell and animal studies to investigate the effect of L. gasseri on a biochemical level. Here are some of their findings:
- Increased IgA in infections , increased the IgG2a/IgG1 ratio , and decreased IgE in allergies .
- Increased TLR2  and BAFF .
- Increased TGF-β , and TNF-α [49, 22, 25, 44] [a study where TNF-α is decreased: 46].
- Increased IL-1β  and IL-2 [22, 20] in infections, but decreased the rate of proliferation and IL-2 production by CD4+ T in allergy .
- Mostly increased IL-6 [48, 25, 44] [a study where it is decreased: 46].
- Decreased IL-8  and IL-17A .
- Increased IL-10 [48, 49, 37, 25], IL-12 [49, 22, 25, 38], IL-15 and IL-21 .
- Increased IFN-γ , and IFNAR .
- Increased perforin 1 .
- Increased intracellular glutathione , and GLUT4 .
- Decreased CCL2, CCR2, Lep, Nos2 , sICAM-1 , ACC1, FAS, and SREBP1 [5, 15].
- Increased high-molecular-weight adiponectin .
- Increased ACO, CPT1, PPARα, PPARδ .
- Increased Mx1 and Oas1a genes, critical for viral clearance .
- Decreased CSF2 .
- Decreased serum amyloid P component .
- Increased PGE2 .
- Increased Th1 cells in allergies .
- Increased CD8(+) T cells, maintained CD8(+)CD28(+) T cells and lymphocyte transformation .
- Inhibited the proliferation of CD4+ T cells and associated inflammatory responses .
Probiotics are generally considered safe. However, the use of probiotics should be avoided in patients with organ failure, immunocompromised status, and dysfunctional gut barrier mechanisms. To prevent adverse side effects, talk to your doctor before starting a new probiotic supplement.