The effect of consuming diets containing beef compared with plant-based beef substitute on human milk composition in the study of nutrition in postpartum and early-life (SUPER) randomized crossover feeding trial

Abstract:

Background: Ultraprocessed foods (UPFs), including plant-based meat substitutes, are marketed as healthy alternatives to whole foods. However, little evidence exists regarding their effects on human milk composition, particularly how dietary UPFs might alter human milk fatty acids.

Objectives: We tested whether replacing beef with an ultraprocessed plant-based beef substitute alters human milk fatty acid profiles.

Methods: In a double-blind, randomized, crossover feeding trial, 17 lactating females whose infants were fed only their milk completed 2 6-d diet phases separated by 6-d washout periods. Participants consumed 339 g (12 oz) daily of beef or plant-based substitute, depending on the diet phase. All meals were prepared in a metabolic kitchen and fully provided. Dietary compliance exceeded 95%. The final human milk samples collected on day 6 of each condition were analyzed for 27 fatty acids. Mean differences in fatty acid percentages were assessed with independent and paired t-tests for intervention food and human milk samples, respectively. Maternal weight, satiety, glucose response, and infant intake were also measured.

Results: Human milk collected during the substitute diet contained higher levels of tropical oil-derived medium-chain saturated fatty acids, such as lauric acid (12:0: 9.32 ± 1.8 compared with 4.47 ± 1.82, P < 0.001) and lower levels of long-chain polyunsaturated fatty acids (LCPUFAs), including arachidonic acid (20:4n-6: 0.35 ± 0.06 compared with 0.41 ± 0.06, P < 0.001) compared with milk form the beef diet. No significant differences were observed in maternal weight, satiety, glucose response, or infant intake.

Conclusions: Replacing beef with plant-based UPF changed human milk fatty acid composition, reducing LCPUFAs and increasing tropical oil-derived saturated fats. These shifts may have implications for infant neurodevelopment and immune function, highlighting the need to distinguish between nutrient-equivalent and biologically equivalent foods in postpartum dietary guidance. This trial was registered at www.