Studies on women’s health still lag behind what exists for men, but Frisch was conducting groundbreaking work on the topic when it was still a taboo. In the 1970s, Frisch was one of the first to study women and how their weight affects fertility, co-authoring a paper in 1974 showing that women’s menstrual cycles can cease if they lose as little as 15 pounds. This also paved the way to the discovery of leptin, a protein that’s foundational to understanding processes like metabolism, puberty, and pregnancy—not to mention everyday functions like burning energy, eating, and exercising. Frisch continued her research at the Harvard Center for Population and Development Studies, and today her theories on fatness and fertility are widely known and accepted. Her son Henry Frisch, a professor of physics at the University of Chicago, says his mother never dwelled on the sexism in the field, though she earned much less than her male colleagues. “She was determined to understand these key biological issues in women’s health,” he says. “Nothing was going to stop her.” Today, women who hope to become mothers as well as athletes often to turn to Frisch’s work to help them better understand their bodies.