Table A.1 displays the demographic characteristics of survey participants. Participants consisted of 392 individuals who reported engaging in peer milk sharing. Demographic data show that nearly 90% of respondents were white. Most participants were college-educated, with 64.6% reporting a bachelor's degree or higher. The sample was also socioeconomically privileged: nearly half of participants reported household incomes above US$70,001 a year and nearly 25% reported incomes above US$100,000 per year. The most common employment status was ‘not employed’, indicating that respondents were likely raising small children at home with the financial support of a spouse, followed by ‘employed full-time’. More than 70% of participants reported having only one or two children (see Table A.2). The majority identified as cisgender (99.7%) and heterosexual (95.3%). All but five of our respondents (99% of the sample) reported participating in peer breastmilk sharing since 2010, the year that Eats on Feets and Human Milk 4 Human Babies first appeared.