As an athlete, failure to consume sufficient energy (total kcals) can lead to a reduction in lean muscle mass.
If your caloric intake is inadequate, your body seeks to reduce the metabolic mass (i.e. lean muscle mass) to make a downward adjustment in the metabolic rate and thereby, reduce your need for calories. Knowing how your body composition changes with weight changes is important. Specifically, understanding if an increase/decrease in fat or an increase/decrease in muscle resulted from a change in weight is important to knowing if your dietary strategy is sufficient and successful. Ideally, you want a decrease in body fat and to maintain or increase lean muscle mass.
While this approach may not result in weight loss as fat weighs less than muscle, it results in improved body composition and better performance.
Source: Benardot, D. (2012). Advanced sports nutrition. Champaign, IL: Human Kinetics.
