As physiatrists, we treat athletes and physically active individuals who may be at increased risk for impaired nutrition. A key concept to understand in optimizing the health of this population is energy availability. Energy availability (EA) is defined as the difference of energy intake to exercise energy expenditure, standardized to fat-free body mass. In exercising women, adequate EA has been defined as 45 kcal/kg of fat-free mass per day and low EA has been defined as less than 30 kcal/kg of fat-free mass per day. Low EA was shown to negatively affect metabolic and reproductive function, including suppressed thyroid function, reduced bone turnover, disruptions in luteinizing hormone pulsatility, and lower sex hormones.1
Recognizing the multiple potential consequences of low EA, the International Olympic Committee proposed a new concept relative energy deficiency in sport (RED-S) in 2014 defined as “impaired physiological functioning caused by relative energy deficiency and includes, but is not limited to, impairments of metabolic rate, menstrual function, bone health, immunity, protein synthesis and cardiovascular health.”2 Relative energy deficiency in sport applies both male and female athletes, including adaptive sports athletes. Relative energy deficiency in sport expands on the concept of female athlete triad (triad), which describes consequences of low EA, including menstrual dysfunction and impaired bone health.3 In 2018, the International Olympic Committee Expert Group provided an updated statement on growing evidence regarding the consequences of low EA in RED-S.2
RELATIVE ENERGY DEFICIENCY IN SPORT (RED-S): 2018 UPDATE
The 2018 RED-S position statement provides updated science on the effects of low EA on health and performance. Individuals with RED-S may experience one or more outcomes from the low EA state. The 10 health consequences are endocrine, growth and development, metabolic, cardiovascular, gastrointestinal, hematological, immunological, psychological, and two triad components of menstrual function and bone health. The 10 potential performance consequences are increased injury risk, impaired judgment, decreased coordination, decreased training response, decreased concentration, depression, irritability, decreased glycogen stores, decreased endurance performance, and decreased muscle strength.
Relative energy deficiency in sport may affect both female and male athletes and nonathlete populations with behaviors related to low EA such as performing artists. Relative energy deficiency in sport also affects para-athletes, a growing sport population that may often receive care from physiatrists. Nutrition may be impaired because of the underlying associated medical conditions from a disability. However, para-athletes face similar circumstances as able-bodied athletes including high-energy demand to participate in sport. In addition, para-athletes may attempt to modify weight for goal of performance such as wheelchair racers. The modified weight bearing status of para-athletes may predispose to issues with low bone density, further highlighting the importance to prevent consequences of RED-S in para-athletes.
WHAT IS THE IMPACT OF RED-S IN PHYSIATRIC CLINICAL PRACTICE?
All athletes and populations at risk for low EA should be screened for risk factors of RED-S and the triad. This includes questions about dietary intake, including special diet or avoiding certain foods. Calcium intake and vitamin D along with other key nutrients should be assessed in evaluation for possible bone stress injury and to prevent secondary complications of impaired bone health. Menstrual history and current menstrual status should be obtained in all women or adolescents to screen for primary or secondary amenorrhea or oligomenorrhea. Screening for the hypogonadal state in male athletes should be considered when clinically appropriate. Further laboratory tests and dual-energy x-ray absorptiometry should be considered in patients with RED-S to help guide management. Management of RED-S should start with nonpharmacological treatment that focuses on meeting with a registered dietician to achieve adequate EA and optimize other aspects of nutrition.2
WHAT QUESTIONS REMAIN OUTSTANDING?
Measures of EA remains challenging to obtain and better screening tests are required. Many of the domains of RED-S require further research to understand the physiology, particularly in men. Prevalence of RED-S is unknown. Limited research has been performed in para-athletes to understand the unique aspects to optimizing health in this population. Future studies that measure the physiological and performance consequences of low EA will help advance our understanding of RED-S. Resulting discoveries may help further refine the treatment of RED-S.
1. Ihle R, Loucks AB: Dose-response relationships between energy availability and bone turnover in young exercising women. J Bone Miner Res
2. Mountjoy M, Sundgot-Borgen JK, Burke LM, et al: IOC consensus statement on relative energy deficiency in sport (RED-S): 2018 update. Br J Sports Med
3. De Souza MJ, Nattiv A, Joy E, et al: 2014 Female Athlete Triad Coalition Consensus Statement on Treatment and Return to Play of the Female Athlete Triad: 1st International Conference held in San Francisco, California, May 2012 and 2nd International Conference held in Indianapolis, Indiana, May 2013. Br J Sports Med