UT Austin study shows breast milk fat profile changed within six days when mothers swapped beef for plant-based meat

A new study from the University of Texas at Austin has found that replacing beef with a plant-based meat substitute altered the fatty acid profile of breast milk in less than a week, even when the rest of the diet consisted of whole, unprocessed foods. The findings, published in the American Journal of Clinical Nutrition, suggested that relatively small dietary changes could influence the types of fats an infant receives during breastfeeding.

The randomized clinical trial involved 24 families in Austin who received all meals from the research team over a 25-day period. The meals were nutritionally balanced and identical except for the protein source: either whole-food beef or a widely available plant-based alternative classified as ultra-processed. While the total amount of fat in participants’ breast milk remained the same, the composition changed depending on the diet.

Mothers who consumed the plant-based product produced milk with lower levels of long-chain polyunsaturated fatty acids, nutrients known to support neurodevelopment, as well as higher levels of saturated fats derived from tropical oils. These oils are commonly used in ultra-processed foods.

“We’ve known that breast milk reflects what moms eat, but we were surprised by how quickly and clearly we saw these changes, and from just one food swap,” said lead author Marissa Burgermaster, Ph.D., Assistant Professor in the Department of Population Health at Dell Medical School. She said the work helped address a gap faced by breastfeeding families looking for evidence-based guidance “in a market full of ultra-processed plant-based alternatives that may not be nutritionally equivalent to whole foods like beef.”

The study is believed to be the first to isolate the effect of an ultra-processed product on breast milk composition within a postpartum diet made largely of whole foods. Burgermaster, who also holds an appointment in nutritional sciences, said the research underscored how food choices intersect with identity, access, and health. “We’re not saying one food is ‘good’ or ‘bad’, but we do want people to know that even foods with similar ‘nutrition facts’ have important differences,” she said. She added that recent epidemiological work has linked ultra-processing to poorer health outcomes, and studies such as this one help clarify why those relationships may exist.

The researchers stressed that while changes in the milk’s fatty acids resembled patterns associated in previous studies with brain and immune development, this study did not measure health outcomes in infants. They noted that the short duration of each diet phase would be unlikely to produce long-term effects for participants’ children.

Beyond the biochemical findings, the team also reported strong engagement from new mothers, a group that is often underrepresented in clinical research. Participants expressed interest in understanding how their diets might influence their babies, highlighting a need for clear, evidence-based advice during lactation.

The study was funded by the National Cattlemen’s Beef Association, a contractor to the Beef Checkoff, and the Texas Beef Council. The authors said neither funder was involved in the study design, data collection, analysis, or publication. Researchers from UT Austin contributing to the work included Summer Messer, Erin Hudson, Madalyn Rosenthal, Heather Leidy, Yan Ning Li, J. Thomas Brenna, Hui Gyu Park, Nitu Dahale, Lisa Kan, Jenna Lan Mai, Elizabeth M. Widen, Lorie Harper, and Michele Hockett Cooper.