For years, Relative Energy Deficiency in Sport (RED-S) was thought of as something that primarily affected young, elite female athletes. We now know that’s simply not true. The takeaway is simple: RED-S is an energy availability issue not an age, gender, or body-size issue. Whether you’re a teenage runner, a 50-year-old Ironman athlete, or a HYROX competitor, proper fueling is essential for long-term health and peak performance.