Benefits
Modest abdominal fat reduction with strain SBT2055 in fermented milk
This is the one benefit with a reference behind it. In a randomized, placebo-controlled trial in adults, a daily fermented milk drink containing L. gasseri SBT2055 reduced abdominal visceral fat area by about 8% from baseline over 12 weeks in 210 Japanese adults who started with above-average abdominal fat, while the group given the same drink without the bacteria did not change. The effect faded within about 4 weeks of stopping, so any benefit lasts only as long as you keep taking it. Keep three limits in mind: the changes were modest, the product tested was a fermented milk drink rather than a capsule, and the research was run and funded by the dairy company that owns the strain. It is a single study, and it does not make L. gasseri a fat loss treatment.
BNR17: a different strain, with no study cited here
BNR17 is a different L. gasseri strain from the one in this page's cited trial, and no reference here supports it. With probiotics the strain is the product, so results for SBT2055 do not transfer to BNR17, and the weight and waist figures previously listed here came from a study that is not cited and was not verified. If a product advertises BNR17 weight loss numbers, ask which specific trial they come from.
H. pylori research on a different strain (not cited here)
LG21 (also called OLL2716) is another separate L. gasseri strain, studied mainly in Japan in people already infected with H. pylori. No study of it is cited on this page, so nothing here supports these claims, and results in infected patients would not describe what a probiotic does for a healthy person anyway. H. pylori infection is a medical condition that needs testing and treatment from a doctor, and a probiotic is not a treatment for it or for gastritis.
Mastitis and infant colic: a different strain, no study cited here
CECT5714 is yet another separate strain, and no reference on this page supports these claims. The comparison against simethicone comes from work that is not cited here and was not verified. Mastitis is an infection that needs medical care, and a baby who cries persistently should be assessed by a pediatrician rather than given a supplement. Never give a live probiotic to an infant without talking to their doctor first.
Mechanism of action
Bile salt hydrolase reducing dietary fat absorption
L. gasseri produces bile salt hydrolase enzymes that deconjugate bile acids in the small intestine. Deconjugated bile acids are less effective at emulsifying dietary fats, reducing fat absorption. This is a proposed explanation drawn mainly from laboratory work. It has not been shown to be the reason for the small changes seen in the one human trial cited on this page.
Adipocyte differentiation inhibition (PPAR-γ modulation)
L. gasseri metabolites (especially conjugated linoleic acid analogues produced by bacterial fermentation) inhibit adipocyte differentiation by suppressing PPAR-γ and CEBP-α transcription factors in cell culture models. This is cell culture work only. It has not been shown to happen in people, and no cited study here measured it.
Anti-inflammatory effects on adipose tissue
One idea being tested is that L. gasseri limits how much bacterial wall material (lipopolysaccharide) passes through the gut wall, which in theory would lower low grade inflammation. This comes from laboratory and animal research. The single human trial cited on this page did not establish changes in inflammatory markers such as TNF-alpha, IL-6 or CRP.
Gasseiricins — H. pylori-suppressing antimicrobials
Laboratory studies show that the OLL2716 and LG21 strains make bacteriocins (called gasseiricins) that can interfere with H. pylori in test systems. This is test tube evidence about strains other than the one in the cited trial, and no human study of it appears on this page.
Clinical trials
Randomized, double-blind, placebo-controlled trial in adults comparing a daily fermented milk drink containing L. gasseri SBT2055 with the same drink without the bacteria. Main outcome: abdominal fat. (Kadooka et al. 2013, Br J Nutr, PMID 23614897. This is the only human study cited on this page.)
Adults with excess abdominal fat, drinking fermented milk containing the SBT2055 strain daily.
Abdominal fat fell modestly in the group drinking the L. gasseri SBT2055 fermented milk compared with the placebo milk. The limitations matter as much as the result: it is a single trial of a single strain, it was funded by the dairy company that owns the strain (Megmilk Snow Brand, formerly Snow Brand Milk Products), the product was a fermented milk drink rather than a capsule, and the changes were small. The 'L. gasseri for weight loss' positioning you see in marketing goes well beyond what this trial showed.
Randomized, double-blind, placebo-controlled trial of L. gasseri BNR17, a different strain from the SBT2055 in the card above (Kim J, Yun JM, Kim MK, Kwon O, Cho B 2018, J Med Food 21(5):454-461, PMID 29688793).
90 adults aged 20 to 75 with a BMI of 25 to 35, randomized to placebo, 1 billion CFU/day or 10 billion CFU/day for 12 weeks.
Visceral fat area fell more on the higher dose than on placebo (a 21.6 cm2 difference at 12 weeks, P = .012), and waist circumference fell from baseline in both BNR17 groups but not in the placebo group. Blood markers did not differ between groups. It is a single trial of one strain, and BNR17 results cannot be credited to SBT2055.
This card described work on CECT5714, a different L. gasseri strain, in infants. It is not among the references cited on this page, was not verified, and the source was listed only as 'related infant colic probiotic trials'.
Infants. No verified study of this strain in infants is cited on this page, and infant use should always be discussed with a pediatrician first.
The crying time numbers previously listed here came from a source that is not cited on this page and was not verified, so they have been removed. What is worth keeping from this section: the probiotic with the better studied record in infant colic is a different species entirely, L. reuteri DSM 17938, and even there the benefit was seen in breastfed infants rather than formula fed ones. Colic in a baby is something for a pediatrician to assess, not something to self treat with a supplement.