The first few months of life are a critical time for setting the health trajectory of both infants and mothers. It is essential that guidance provided to new families be based on the most rigorous scientific evidence available. Beef serves as a highly nutrient-rich option for lactating women. Plant-based beef products have similar nutrient profiles, and some consumers perceive them as a healthier alternative to traditional beef. This study aims to understand the different effects that beef and plant-based beef have on breastmilk composition, maternal glycemic control, maternal intake and satiety, and infant intake. Understanding the differences between beef and plant-based beef can help parents make informed decisions about optimal nutrition for their infants and themselves.

During the initial months of life, it is critical to set a path towards a healthy future for both the infant and mother.1-4 It is essential to provide new families with guidance that is grounded in the most rigorous scientific evidence possible. Although beef is a highly nutritious option for lactating women, there are now many plant-based beef products with similar nutrient profiles. Some consumers consider these substitutes to be a healthier alternative to beef. 5 "Plant-based" meat alternatives have become a common component of many Americans diets.5 A controlled trial is necessary to explore differences between beef and plant-based beef.

There have been no trials to establish differences in biochemical compounds available to breastfeeding infants in human milk based on lactating mothers' consumption of meat vs. plant-based meat. Furthermore, the amounts of compounds related to plant-based meat analogues that are transferred from a mother's diet into her breastmilk have also not been examined. While maternal weight status is increasingly linked to milk composition and differences in infant weight status,6-9 the role of diet in these associations has not been studied. These differences in breastmilk composition related to infant weight could explain inconsistent influence of breastfeeding on later weight status. Identifying possible biomarkers transferred from mothers to infants in breastmilk would elucidate potential biological mechanisms to explain the diet-weight relationship.

Finally, while some studies have linked metabolic dysregulation such as obesity or diabetes to negative alterations in breastmilk composition,3,7,10-13 we are not aware of any studies that consider whether the deleterious effects are attributable to glycemic control. Differences in ingredients and processing could lead to a differential effect on glycemic response in meat vs. plant-based meat.14-17 Such a finding would contribute to understanding the mechanisms by which maternal postnatal health and diet influence infant development.

This pilot study will help plan for future studies related to this population.

Maternal Inclusion Criteria:

1. Comfortable communicating in English, both orally and in writing
2. Infant aged between 6 and 12 weeks at enrollment
3. Exclusively breastfeeding one infant
4. Intention to continue breastfeeding through duration of the study
5. BMI between (18.5 - 29.9) OR BMI 30 - 35 and willing to consume an additional ~240 calories to ensure against caloric deficit
6. Willing to consume both meat & plant-based meat products
7. Residing within ~10 mi radius of UT

Infant Inclusion Criteria:

1. Exclusively breastfeeding
2. Birth weight ≥ 2.5kg (5.5 lbs)

Maternal Exclusion Criteria:

1. Pre-gestational diabetes, previous diagnosis of diabetes, or history of GDM (need specific diet)
2. Negative delivery outcome (post-delivery stillbirth, infant mortality)
3. Began complementary feeding or intends to begin feeding solid food before completion of study, infant age <16 weeks.
4. Active eating disorder (atypical diet quality, anxiety about diet and weight/body measurements and weight gain)
5. Active substance abuse with alcohol or drugs by self-report (risk for poor adherence and could impact outcomes)
6. Treatment with medications (e.g., corticosteroids, anti-psychotics) known to have metabolic/body weight effects
7. BMI <18.5 or >35kg/m2
8. Unable or unwilling to follow protocol
9. Mom following vegetarian, vegan, or strict exclusion diet during pregnancy or lactation
10. Excessive caffeine consumer
11. Not a good candidate for a feeding trial (In general, if there are a variety of things indicating the potential participant might have a hard time meeting the requirements for the diet intervention. For example, if during screening, the potential participant indicates something that suggests they would be dishonest about their adherence to the diet.)

Infant Exclusion Criteria:

1. Preterm or in NICU post birth for >72 hours
2. Low birth weight < 2.5 kg
3. Negative health outcome following delivery that could affect breast feeding