Myth-buster
In a 136-person RCT, Lactobacillus reuteri supplements did not change human milk oligosaccharide levels in colostrum or mature milk.
This null result challenges the popular idea that probiotic strains like L. reuteri can directly shape the complex sugar profile of breast milk — but because this is among the first controlled trials on this specific pairing, the picture is far from settled.
Researchers gave pregnant women a probiotic containing Lactobacillus reuteri (along with omega-3 fatty acids) and then measured human milk oligosaccharides — prebiotic sugars in breast milk that help shape a baby's gut microbiome. Three months after birth, they found the probiotic had no detectable effect on HMO levels in either early colostrum or mature milk, despite the common expectation that probiotics boost these compounds.
Where this fits in the evidence
This is among the first studies we've indexed on Lactobacillus reuteri for Increased Human Milk Oligosaccharide Level — treat it as an early signal until more research accumulates.
The study
- Randomized Controlled Trial (RCT)
- n = 136
- 2025-08
- Pediatric allergy and immunology : official publication of the European Society of Pediatric Allergy and Immunology
- PubMed: 40747696
- DOI: 10.1111/pai.70162
- Full study breakdown →
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