Tennis star’s diagnosis sheds light on little known illness that predominantly affects women

Tennis star Emma Navarro recently announced she was stepping back from her 2026 season to focus on her health after she was diagnosed with relative energy deficiency in sport, known as RED-S. Little is understood about the disease, which primarily affects women and happens when the body doesn’t get enough energy from food to fuel both exercise and essential daily functions. It’s more common in endurance athletes like cyclists and runners who are particularly lean, and can cause fatigue, muscle and join pain, weight gain and mental health issues. Navarro outlined her experience, which she said included a weakened immune system and memory loss, and is drawing attention to the disease, which remains barely studied and most people have never heard of, including physicians.