Context:In most combat sports, athletes are classified according to their body weight, and many of them attempt to lose weight quickly. Objectives: Since the effects of rapid weight loss (RWL) on competitive performance are somewhat ambiguous, this study aims to review high-risk behaviors used for RWL, to assess food intake and anthropometric data in combat sports athletes, and to investigate the negative effects of RWL on physiological and health-related parameters. Methods: This systematic review study was conducted by searching the PubMed, Science Direct and Scopus databases using keywords, including (combat sports, RWL, high-risk behaviors) and (food intake, anthropometric measurements) from 2001 to 2017. After screening based on the title and abstract of identified studies, 17 articles met our inclusion criteria and were included in this review. Results:The results of the studies indicated a high prevalence of RWL among athletes, which was often due to reduced body fluids. At the same time, lower-level athletes often used more dangerous methods, such as fasting, skipping meal, and fluid restriction. This method can negatively affect athletes' mental status and athletic performance. Conclusions: Regarding the negative effects of short-term adjustment of weight on physiological and mental function, further studies suggest athletes to consume a balanced and varied diet including all food groups.