This chapter reviews the main issues and concerns about weight-loss strategies aimed to achieve a target weight and adiposity and its respective minimum values. It highlights objective methodologies for energy expenditure assessment, and presents and discusses the relevance of body composition in performance, and the major health consequences of athletes engaged in weight-sensitive sports. The chapter provides tools for sports professionals to counteract the currently used negative practices leading to enhanced health and performance of the athletes. Athletes competing in weight-sensitive sports commonly present a low weight and adiposity. The most common studies regarding weight class sports have been conducted to understand the impact of short-term weight reductions on body composition and on athletes' performance. The benefits of participating in sports are recognized among adolescents and adult female athletes but it is important to assure adequate nutrition to avoid compromising reproductive and skeletal health.