Researchers studied how eating plant-based beef substitutes affects the nutrients in breast milk. Seventeen breastfeeding mothers ate either real beef or a processed plant-based beef substitute for 6 days at a time, with breaks in between. The study found that when mothers ate the plant-based substitute, their milk had more saturated fat from tropical oils but less of certain healthy fats that babies need for brain development. The real beef diet produced milk with a better balance of nutrients. This research suggests that just because two foods seem similar doesn’t mean they affect our bodies the same way.

The Quick Take

  • What they studied: Whether eating plant-based beef substitutes instead of real beef changes the fatty acids (healthy fats) in breast milk
  • Who participated: 17 women who were breastfeeding babies that only drank breast milk, who completed the full study with very high compliance to the diet plan
  • Key finding: Breast milk from mothers eating plant-based substitute had significantly higher levels of saturated fat from coconut and palm oils (lauric acid increased from 4.47 to 9.32, p<0.001) but lower levels of important brain-building fats like arachidonic acid (decreased from 0.41 to 0.35, p<0.001)
  • What it means for you: If you’re breastfeeding, the type of protein you eat may matter for your baby’s nutrition. Plant-based substitutes aren’t nutritionally identical to real beef, even though they’re marketed as healthy alternatives. This doesn’t mean you can’t eat plant-based foods, but it suggests choosing whole plant foods over ultra-processed versions may be better for breast milk quality.

The Research Details

This was a carefully controlled feeding study where 17 breastfeeding mothers participated in two separate 6-day eating periods. During one period, they ate 12 ounces of real beef daily, and during the other period, they ate the same amount of plant-based beef substitute. The two periods were separated by 6-day breaks to let their bodies reset. All meals were prepared in a special kitchen to ensure exact portions and ingredients. The mothers didn’t know which diet phase they were in (called “double-blind”), and researchers collected breast milk samples on the last day of each phase to test the fatty acid composition.

The researchers measured 27 different types of fatty acids in the milk samples and compared them between the two diet phases. They also tracked whether the mothers’ weight changed, how full they felt, their blood sugar responses, and how much milk their babies drank. The study had excellent compliance, meaning mothers stuck to the diet plan over 95% of the time.

This research design is important because it controls almost all variables except the main food being tested. By providing all meals and having mothers eat in a specific order with washout periods, researchers could be confident that any milk changes came from the beef versus substitute difference, not from other diet factors. This level of control gives us more reliable answers than simply asking people what they eat.

Strengths: Small but well-controlled study with excellent dietary compliance (>95%), double-blind design to prevent bias, published in a respected nutrition journal, and measured multiple milk components. Limitations: Only 17 participants (relatively small), only tested one type of plant-based substitute, only measured milk composition on one day per phase, and didn’t follow babies long-term to see if the milk changes affected their development.

What the Results Show

When mothers ate the plant-based beef substitute, their breast milk contained significantly more lauric acid (a saturated fat from coconut and palm oils), jumping from 4.47% to 9.32% of total fatty acids. This is more than double the amount. At the same time, the milk contained less arachidonic acid (a long-chain polyunsaturated fat important for brain development), dropping from 0.41% to 0.35%.

The shift toward more tropical oil-derived saturated fats and away from brain-building polyunsaturated fats represents a meaningful change in milk composition. These aren’t tiny differences—they’re substantial enough that researchers consider them significant. The pattern suggests that plant-based substitutes, which often contain coconut and palm oils, directly transfer these fats into breast milk.

Interestingly, the mothers themselves didn’t experience obvious changes. Their weight didn’t change significantly, they reported similar feelings of fullness, their blood sugar responses were comparable, and their babies drank the same amount of milk. This shows that changes in milk composition can happen without mothers noticing obvious effects on their own bodies.

The study measured 27 different fatty acids total, but the most important changes were in the saturated fats from tropical oils and the long-chain polyunsaturated fats. The researchers didn’t report major changes in other fatty acid categories, suggesting the effect was specific to these types of fats. No differences were found in maternal weight gain, hunger levels, blood sugar control, or infant milk intake, indicating the substitute didn’t affect these practical measures.

This research adds to growing evidence that ultra-processed foods affect our bodies differently than whole foods, even when they’re nutritionally similar on paper. Previous studies have shown that plant-based meat substitutes contain different ingredients (especially tropical oils) than real meat, but this is one of the first studies to show how these differences actually change breast milk composition. The findings support the idea that ’nutrient-equivalent’ foods (similar nutrition labels) aren’t always ‘biologically equivalent’ (same effects in the body).

The study only included 17 women, which is a small group, so results might not apply to all breastfeeding mothers. Only one brand or type of plant-based substitute was tested, so other products might have different effects. Milk was only tested on one day per diet phase, so researchers didn’t see how fatty acids changed over time. The study didn’t follow babies to see if these milk changes actually affected their brain development or health. Finally, the study lasted only 6 days per phase, so we don’t know what happens with longer-term consumption.

The Bottom Line

For breastfeeding mothers: Consider prioritizing whole foods like real beef, fish, eggs, and whole plant foods over ultra-processed plant-based substitutes. If you prefer plant-based eating, focus on whole plant proteins (beans, nuts, seeds, tofu) rather than processed meat substitutes. This is a moderate-strength recommendation based on this single study. For infant nutrition: This research suggests that what mothers eat during breastfeeding matters for milk quality. Parents should know that breast milk composition can change based on maternal diet, which is one reason maternal nutrition during breastfeeding is important.

Breastfeeding mothers should pay attention to this research, especially those considering plant-based diets or meat substitutes. Parents of infants who are exclusively breastfed should understand that maternal diet affects milk composition. Healthcare providers advising postpartum women should consider discussing whole food options versus processed alternatives. People interested in plant-based eating can still benefit from this research by choosing whole plant foods instead of ultra-processed versions.

Changes in breast milk fatty acid composition appear to happen relatively quickly—within 6 days of dietary change in this study. If a breastfeeding mother switches her diet, the milk composition may shift within a week. Benefits or concerns related to these changes would likely develop over weeks to months as babies consume the altered milk, though this study didn’t measure long-term infant outcomes.

Want to Apply This Research?

  • Track daily protein sources consumed (real beef, poultry, fish, eggs, beans, nuts, or plant-based substitutes) and note the specific product names and brands for processed foods. Rate energy levels and milk supply satisfaction daily on a 1-10 scale to correlate with dietary choices.
  • If breastfeeding, gradually replace ultra-processed plant-based meat substitutes with whole protein sources: swap one plant-based burger per week for grilled chicken, baked fish, scrambled eggs, or a hearty bean-based meal. Track which whole foods you enjoy most to build sustainable habits.
  • For breastfeeding mothers: Keep a weekly food diary noting protein sources and any changes in milk supply, energy, or infant feeding patterns. If making dietary changes, monitor for 2-3 weeks to observe any shifts in how you feel or how your baby feeds. Consider discussing significant dietary changes with your healthcare provider or registered dietitian.

This research suggests that plant-based beef substitutes change breast milk composition differently than real beef, but it’s based on a small study of 17 women over a short time period. The long-term effects on infant health and development are not yet known. Breastfeeding mothers should not make major dietary changes without consulting their healthcare provider or a registered dietitian, especially if they have concerns about milk supply or infant nutrition. This study does not mean plant-based diets are unhealthy for breastfeeding—it suggests choosing whole plant foods over ultra-processed versions may be preferable. Individual responses to different foods vary, and what works best depends on each mother’s health, preferences, and circumstances. Always discuss dietary concerns with your doctor or lactation consultant.