Dietary choices nursing mothers make have a direct impact on the health of their baby so it's important they make wise decisions. Researchers at the University of Texas found it doesn't take long for the breast milk of mothers eating plant-based meat to negatively alter what their babies are consuming.

The report in the The American Journal of Clinical Nutrition showed that it took only six days to change the fat composition of breast milk of mothers when they ate plant-based meat.

UT scientists conducted the randomized clinical trial involving 24 families over a period of 25 days. The study subjects ate identical nutritionally balanced diets of unprocessed foods. The only difference was the protein source, which was either whole-food beef or a popular plant-based meat substitute, which is considered highly processed.

The total fat content for both diets was similar, but the types of fats found in the breast milk was different. Those who consumed the meat substitute had lower levels of long-chain polyunsaturated fatty acids, which studies show are important for the neurodevelopment of babies. At the same time, they had higher levels of saturated fats from tropical oils, which are commonly found 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 Marissa Burgermaster, Ph.D., lead author of the study and assistant professor in the Department of Population Health at Dell Medical School. "This kind of research helps fill an important gap for breastfeeding families who want to make informed decisions, especially in a market full of ultra-processed plant-based alternatives that may not be nutritionally equivalent to whole foods like beef."

Researchers said this is the first study of its kind designed to look at the effects of ultra-processed food on breast milk composition.

"As a behavioral nutrition scientist, I'm always thinking about how food choices intersect with health, identity and access," said Burgermaster. "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. In the past few years, we have seen many epidemiological studies demonstrate relationships between ultra-processing and poorer health outcomes. Now we are starting to get closer to uncovering just how much they matter and why."

Click here to read more in The American Journal of Clinical Nutrition.