The 100-family trial will measure whether a small daily amount of donor breast milk shifts a formula-fed infant's gut toward a healthier, more breastfed-like pattern

Leche, the first shelf-stable, consumer-driven donor breast milk, and Tiny Health, the at-home microbiome testing company for every stage of life, today announced a joint clinical study examining how donor breast milk affects gut health in formula-fed infants. It is among the first studies to apply modern microbiome science to donor milk specifically, and the first to measure what happens when a small daily amount is added on top of formula.

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Leche's donor breast milk sachets alongside Tiny Health's Gut Health Test, the tools families will use as part of the new joint study. Leche is 100% human donor breast milk powder from medically screened donors, triple-tested at every stage for safety and quality, processed in an FDA-registered facility following GMP guidelines. Each convenient 8g sachet reconstitutes into 2oz of breast milk, making it easier and safer to access donor milk.

"For years the conversation has been breast versus formula, as if those are the only two options a family gets," said Trish Clifford, co-founder of Leche. "Most parents end up somewhere in between, and until now nobody has actually studied what that middle ground does for a baby's health. We built Leche because donor milk deserved to be a safe and accessible option instead of a workaround. This study is about giving that option the science to back it up."

The science on breast milk's role in infant gut development is well established. A baby's gut is home to trillions of bacteria, and establishing the right ones early is linked to better digestion, immunity and long-term health. Research consistently shows that even a little breast milk helps grow those protective bacteria, largely because of human milk oligosaccharides, a family of roughly 150 to 200 sugars unique to breast milk that feed the gut's good bacteria directly. Formula can now replicate one or two of them, but real breast milk, including powdered donor milk, delivers the full range, since the sugars survive pasteurization intact.

What has not been established, and what this study hopes to prove, is whether a modest daily amount of donor milk, layered into a formula-fed baby's routine, moves the needle for the roughly two-thirds of American babies who receive and rely on formula at some point in their first year.

"This is one of the first studies to examine whether adding a small, consistent amount of donor breast milk to an otherwise formula-fed infant’s diet can produce measurable shifts in microbiome composition and function,” said Cheryl Sew Hoy, Founder and CEO of Tiny Health. “Using shotgun metagenomics, we are eager to see whether babies’ gut microbiomes become better equipped to use the unique sugars found in human milk—and whether even a small daily amount can help beneficial bacteria take hold during this important window of development.”

The study follows a straightforward before-and-after design. Tiny Health will test 100 healthy, full-term, formula-fed babies' guts at enrollment, families will add Leche powdered donor breast milk to daily feeds for a month, and Tiny Health will retest independently at the end. Researchers will look at whether levels of Bifidobacterium, the beneficial bacteria that dominate a healthy breastfed baby's gut, increase, whether the gut becomes better equipped to use breast milk sugars, and whether the overall microbiome shifts toward a more breastfed-like pattern.

Sign-ups open officially August 1 and will close at 100 participants or August 15, whichever comes first. Enrolled families will begin the study in September, with results expected later this year.

Learn more information about the study and sign up for the waitlist HERE. For more information about Leche, visit itsmyleche.com or follow them on Instagram, Facebook and TikTok. For more information about Tiny Health, visit tinyhealth.com and poweredbytiny.com.

About Leche

Leche pioneered shelf-stable, consumer driven donor breast milk, and remains the category leader in making real donor breast milk accessible to everyday families. Founded by mothers and breast milk donors Jenney Korasick and Trish Clifford, Leche is modernizing breast milk through an innovative freeze-drying process that preserves its nutrients while giving parents the ultimate flexibility in feeding. Leche is available direct-to-consumer at itsmyleche.com and is FSA/HSA eligible. For more information, visit itsmyleche.com or follow them on Instagram, Facebook and TikTok.

About Tiny Health

Tiny Health is advancing lifelong health, from the first 1,000 days to the last, and addressing chronic disease through precision microbiome science. Founded in 2020 and built by microbiome scientists and physicians, its testing platform reveals whether your microbiome is trending toward resilience or imbalances using shotgun metagenomics, proprietary AI, and one of the world's largest longitudinal datasets. Trusted by families and health practitioners alike, its research-backed gut and vaginal tests are redefining the microbiome as a cornerstone of personalized health through every life stage. Learn more at tinyhealth.com and poweredbytiny.com.

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"For years the conversation has been breast versus formula, as if those are the only two options a family gets. We built Leche because donor milk deserved to be a safe and accessible option instead of a workaround."