Recently, Mary Cain, the one-time “fastest girl” in America, courageously came forward to bring to light how calorie restriction and a singular focus on weight and body composition are a danger to health and human performance.

When athletes like Mary habitually consume fewer calories than are needed to fuel the demands for health, training, and recovery, a condition called Relative Energy Deficiency in Sports (RED-S) occurs, which impacts many elements of health and performance.

The body is a survival machine that has many systems in place to dictate where and how we use the fuel we ingest depending on what conditions the body is in. Energy availability (EA) is the term that describes the number of calories remaining for body functions after deducting for calories used during exercise and recovery.

Although our bodies can occasionally handle expending significantly more calories than we take in – running a marathon, for example – when we consistently fail to meet our body’s need, RED-S can occur. 

Situations like Mary’s that promote negative relationships with food and body weight highlight the dangers that can arise when coaches and athletes are making decisions that impact long-term health and wellness without the guidance of licensed medical professionals.

For far too long, there has been a prevailing thought in the coaching world that there is a specific height, weight, or body composition that leads to optimal performance.

This proposition simply isn’t accurate; we are all different and “optimal conditions” vary from person to person. Just as history shows that you can win a Super Bowl as a 5’11” quarterback or a 6’6” quarterback, the ranges of weight and body composition are variable across high performance in every sport.

As the profession of sports medicine continues to grow, so does awareness of the dangers of RED-S.  Over the past decade a staggering increase in the availability of sports dietitians and sports psychologists to athletes at the collegiate, pro, and Olympic level is empowering athletes to understand and take control not only of their performance, but also of their health and wellness.

Although there is a common assumption that athletes are “healthy,” research continues to show athletes are deficient in calories, vitamins, minerals, and fats.

Meeting energy requirements for athletes is no doubt challenging, especially teen athletes who are still growing. Athletes, parents, coaches, and health-care professionals should be aware of the health implications that arise when calorie intake does not meet the energy needs of training, competition, and normal growth.

When an athlete has low EA, performance can suffer, injuries can increase, and most importantly – normal health can be adversely affected. After all, we can’t talk about human performance without first taking care of the human.

I often explain RED-S to athletes as a “metabolic injury” that should be given as much attention as a physical injury when trying to return to peak performance.

The risk for RED-S is significantly higher than most athletes realize. And it doesn’t take a toxic training environment or an intent to withhold calories for RED-S to develop.

Taking in as few as 300-500 calories below energy needs every day is enough for impairment of performance and health. At the collegiate level, 10-38 percent of males and 35-58 percent of females are at risk for disordered eating and low energy availability.1

RED-S was initially known as Female Athlete Triad, consisting of three interrelated components:  energy availability, menstrual function, and bone health. 

Because low energy availability impacts athletes of both genders, and more disordered health and performance elements have been identified, the International Olympic Committee (IOC) now identifies the condition as RED-S and has added to it several physiological impairments, including metabolic rate, immune function, protein synthesis, and cardiovascular health.2 In simple terms, RED-S results when caloric intake is insufficient to support daily activity, health, and healing.

Bone health is a significant concern in athletes, particularly for growing teens, given that the capacity to build bone mass is at its highest during teenage years. Insufficient EA can decrease bone mass, and a diet focused on intentionally restricting calories is often low in calcium and vitamin D, two nutrients essential to bone health.

When EA is low, estrogen and testosterone levels can fall, leading to hormonal changes and irregular or missed menstrual cycles. Athletes should be aware of changes in their EA caused by factors such as training load, performance goals, in-season versus off-season needs, intentional or unintentional decreases in caloric intakes, and response to injury or illness.

A study of elite endurance athletes training for the 2016 Olympics found that when female athletes missed their menstrual cycles, or men were in the lowest 25 percentile of testosterone levels, the risk for stress fractures was 4.6-times greater.3

You can take control of your health by testing your testosterone levels with an at-home testosterone test. Athletes will often notice a change in performance before they recognize a health-related issue. The IOC’s position statement on RED-S identifies multiple adverse effects:

  • Decreased muscle strength
  • Decreased glycogen stores
  • Decreased endurance performance
  • Decreased training response
  • Increased injury risk
  • Decreased coordination
  • Decreased concentration
  • Depression and irritability

RED-S puts every athlete at risk. Although most of the research is on female athletes, low EA can impact testosterone levels in men. Unlike missed menstrual cycles in female athletes, hormonal changes in male athletes often go unnoticed.

The IOC identifies the following factors to help ensure low-risk participation in sports:

  • Healthy eating habits with appropriate EA
  • Normal hormonal and metabolic function
  • Healthy bone density
  • Healthy musculoskeletal system

Moderate-risk factors in sports participation include:

  • Prolonged low-percent body fat
  • One month’s weight loss of 5-10 percent
  • Changes in expected growth and development in adolescent athletes
  • Abnormal menstrual cycle
  • Abnormal hormone profile in males
  • Reduction in bone density
  • History of one or more stress fractures associated with hormonal dysfunction and/or low EA
  • Physical/psychological complications related to low EA/disordered eating
  • Prolonged relative energy deficiency
  • Disordered eating behaviors negatively affecting team members
  • Lack of progress in treatment and/or non-compliance

Athletes and their parents should work with their coaches and health-care professionals to assess the demands of their sport and its training and adapt caloric intakes to best meet the performance and health needs of the athlete.


  1. Mountjoy M, Sundgot-Borgen JBurke L, et al. The IOC consensus statement: beyond the Female Athlete Triad--Relative Energy Deficiency in Sport (RED-S). Br J Sports Med.2014 Apr;48(7):491-497.
  2. The National Center on Addiction and Substance Abuse (CASA) at Columbia University. Food for Thought: Substance Abuse and Eating Disorders. The National Center on Addiction and Substance Abuse (CASA) Columbia University; New York: 2003.[accessed Nov. 25, 2019]
  3. Heikura I, Uusitalo A, Stellingwerff T, et al. Low energy availability is difficult to assess but outcomes have large impact on bone injury rates in elite distance athletes. Int J Sport Nutr Exerc Metab 2018;28(4):403-411.