A small randomized trial has found that swapping beef for a plant-based meat alternative changed the types of fats present in breast milk in just six days. The research, published in the American Journal of Clinical Nutrition, offers an early look at how everyday food choices may influence the fats infants receive during breastfeeding.
The study was funded by the National Cattlemen’s Beef Association and the Texas Beef Council, which had no role in the study design, data collection, analysis or publication decisions.
Researchers from the University of Texas at Austin provided 24 breastfeeding families with fully prepared meals over a 25-day period. The meals were designed to be identical in every way except for the main protein source. One phase included whole-food beef. The other phase used a popular plant-based meat made with tropical oils and classified as ultraprocessed. Total fat in the diets did not change across phases.
What did change was the fatty acid profile of breast milk. Mothers who ate the plant-based product had lower levels of long-chain polyunsaturated fatty acids, which help support infant brain and immune development, and higher levels of saturated fats commonly found in tropical oils.
“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. She added that the study helps fill a gap for families navigating a growing market of plant-based substitutes. “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.”
The trial isolated the effect of one specific plant-based meat rather than ultraprocessed foods as a whole. Nutrition researchers note that plant-based products vary widely in ingredients and nutrient profiles, and that an ultraprocessed designation does not inherently determine health impact. In this study, differences in fats likely reflect the product’s specific formulation rather than processing alone.
The researchers emphasized that the study did not measure infant outcomes, and that the short intervention period would be unlikely to produce meaningful long-term effects for the babies involved. Still, the detectable shift in milk composition highlights how quickly maternal diet can influence breast milk.
Beyond the laboratory results, the research team noted strong enthusiasm among participants to learn how their diets affect their babies. Many expressed a desire for clearer and more practical dietary guidance during lactation, an area that often lacks tailored and evidence-based recommendations.
The main takeaway is that breast milk composition responds quickly to maternal diet, and different protein choices can contribute different types of fats. The findings underscore that nutrient profiles and ingredient differences matter more than whether a food is plant-based or animal-based, or whether it’s classified as ultraprocessed.
As with most research on diet and breastfeeding, individual needs vary. Families making decisions about protein sources can consider cost, access, dietary patterns, cultural preferences and health goals, knowing that a wide range of foods can support infant development within a balanced diet.