Postnatal Exercise to Activate Baby's Brown Fat

Epidemiological studies suggest that breastfeeding protects against risk of obesity, diabetes, asthma, and other childhood diseases. However, the specific compounds within breastmilk that are responsible for its protective effects are not fully understood. Moreover, prior work from this investigative team has shown that human milk composition varies substantially between individuals according to factors such as body mass index (BMI), diabetes status, diet, and physical activity. Gaining a better understanding of how modifiable risk factors may impact human milk composition would have the potential to identify strategies to enhance the health-promoting benefits of human milk.

In this project, the investigators will study the impact of maternal exercise on human milk composition. The central hypothesis is that maternal exercise induces changes in breast milk metabolites and lipids that result in activation of infant brown fat, increased infant energy expenditure, and reduced obesity risk.

The study will include assessments of habitual activity during pregnancy and the postpartum period, supervised bouts acute moderate exercise, as well as analysis of human milk composition, infant growth and body composition, and infant energy expenditure.

Inclusion criteria

• 18-45 y of age at the time of enrollment
• Pre-gravid or first trimester BMI 18.5 -40 kg/m2
• Uncomplicated singleton pregnancy
• Intention to exclusively breastfeed for >3 months and, if parity >1, that they successfully breastfed a previous pregnancy
• Term pregnancy (gestational age 37 to <42 weeks)
• Infant with birth weight >10th percentile of weight for gestational age

Exclusion criteria

• Any obstetric contra-indication to exercise at 1 month
• Diagnosis of uncontrolled (HbA1c >7%) type 1 or type 2 diabetes, or gestational diabetes managed with insulin
• Intrauterine growth restriction
• Pre-eclampsia or other pregnancy complications
• Alcohol, cannabis or tobacco use
• Known congenital metabolic, endocrine disease, or congenital illness affecting infant feeding/growth
• Major fetal anomalies
• Musculoskeletal issues that would make exercise difficult