Under-fueling and Relative Energy Deficiency in Sport: Why Your hemaglobin A1c Might Be High, Even If You’re an Endurance Athlete

Endurance athletes are often viewed as models of health and performance. Preparing for an ultramarathon, century ride, or Ironman requires far more than dedication and countless hours of training. It demands planning, recovery, nutrition, and careful structure. From the outside, it looks like the embodiment of discipline and resilience.

Yet in nearly a decade of working as a Registered Dietitian at the intersection of eating disorders and endurance sport, I’ve seen a different reality play out in the lab results of athletes. Many arrive in my office confused by findings such as elevated LDL cholesterol or rising hemoglobin A1c, which are markers more commonly associated with metabolic disease. Read on to learn why this occurs.