Excess energy — that is, extra calories — can be used to build muscle mass, which supports both health and performance. It could also contribute to added body fat, which may or may not improve someone’s health or performance. Weight-class athletes may also need to consider how weight gain will affect their performance and competitive advantage.
Eating too few calories can lead to the negative health and performance consequences of RED-S. Not only will your performance, recovery, and mental health suffer, but you’ll also be at greater risk of injuries or illnesses that will prevent you from training at all.