Low Energy Availability (LEA) arises from the inability to cover energy needs and requirements of training or normal physiological functions. This value differs from the energy balance, which takes into account the total daily energy intake compared to all the energy expended, regardless of the amount of fat-free mass. Insufficient energy consumption affects recovery, adaptation processes, increases the risk of injury or illness, so all of this can negatively affect performance. This mini-review is written on research articles in Pubmed database related to LEA in endurance-trained men and its impact on performance and testosterone. This article also clarifies the prevalence of LEA in male endurance athletes and its correlation to Relative Energy Deficiency in Sports (RED-S). LEA occurs in male endurance athletes and correlates with decreased testosterone levels, decreased bone density and also Resting Metabolic Rate. In endurance-trained men, there is great potential for the negative consequences of low energy availability. It can also be said that there are possibilities for primary screening, so we recommend regular check-ups of blood markers, body structure and keeping not only training but also dietary records, which can increase awareness of an adequate energy balance.