But believe it or not, obesity isn't the reason why the Americans' golden arches are so super-sized. The report noted that while larger cup sizes in countries such as England and Spain are tied to body weight, women born in the U.S. and Canada, including athletes, had bigger boobs regardless of what their scales said. This is because white North American breasts tend to be rounder than the racks of white women born in other countries, and rounder boobs have more volume.