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The term Relative Energy Deficiency in Sport was introduced by the International Olympic Committee in 2014. It refers to the potential health and performance consequences of inadequate energy for sport, emphasizing that there are consequences of low energy availability (EA; typically defined as <30 kcal·kg−1 fat-free mass·day−1) beyond the important and well-established female athlete triad, and that low EA affects populations other than women. As the prevalence and consequences of Relative Energy Deficiency in Sport become more apparent, it is important to understand the current knowledge of the hormonal changes that occur with decreased EA. This paper highlights endocrine changes that have been observed in female and male athletes with low EA. Where studies are not available in athletes, results of studies in low EA states, such as anorexia nervosa, are included. Dietary intake/appetite-regulating hormones, insulin and other glucose-regulating hormones, growth hormone and insulin-like growth factor 1, thyroid hormones, cortisol, and gonadal hormones are all discussed. The effects of low EA on body composition, metabolic rate, and bone in female and male athletes are presented, and we identify future directions to address knowledge gaps specific to athletes.
Elliott-Sale is with Musculoskeletal Physiology Research Group, Sport, Health and Performance Enhancement Research Centre, School of Science and Technology, Nottingham Trent University, Nottingham, United Kingdom. Tenforde is with the Dept. of Physical Medicine & Rehabilitation, Spaulding Rehabilitation Hospital, Brigham and Women’s Hospital, and Harvard Medical School, Boston, MA. Parziale, Holtzman, and Ackerman are with the Division of Sports Medicine, Boston Children’s Hospital, Boston, MA. Ackerman is also with the Neuroendocrine Unit, Massachusetts General Hospital, Massachusetts General Hospital, and Harvard Medical School, Boston, MA.