Calloway was a prominent American nutritionist from the 1960s to the 1990s at the University of California at Berkeley. There, she and Sheldon Margen ran the “Penthouse” studies for 17 years in a three-bedroom apartment atop a university building that had originally been built to teach young women how to manage a household. Six volunteers would stay for a 100 days at a time to have their protein and energy requirements measured. Participants included elderly, menstruating, and pregnant volunteers. Early on, Calloway discovered that Americans were consuming about twice the level of protein their bodies needed. In her later career, Calloway studied the functional consequences of marginal malnutrition in the developing world.