RED-S: The New and Improved Female Athlete Triad

by Alida Iacobellis MHSc RD, special to

Alida Iacobellis

The Female Athlete Triad was once the term we used to describe the interplay between disordered eating, irregular menstrual cycles, and low bone mineral density that is seen in female athletes. Since the research backing this phenomenon was first conducted in the 1980s, advances in science have uncovered the root cause of this grouping of symptoms and discovered that the condition is more complex and far-reaching than we once thought.

What is RED-S?

Relative Energy Deficiency in Sport (RED-S) is the term used to describe the root cause of a range of performance depleting symptoms common in athletes who are under-nourished.

Low energy availability lies at the center of RED-S, and it is directly related to a whole host of complications that can result when athletes aren’t adequately fueled, not only for their athletic performance, but to sufficiently meet their body’s physiological needs to support healthy functioning.

What is Energy Availability?

Energy availability is the difference between energy intake (food) and energy expenditure (exercise). There are two key factors to consider when interpreting this calculation; one, energy expenditure refers to that which is in excess of the energy required for activities of daily living, and two, that the result must be interpreted in relation to fat free mass, or muscle mass.

Research has shown that optimal energy availability is achieved around 45 kcal/kg of fat free mass. Low energy availability occurs when energy availability approaches 30 kcal/kg of fat free mass or lower. This is the point at which an athlete is considered to be impacted by RED-S.

Adequate Energy Availability Promotes Optimal Athlete Health


Where the Female Athlete Triad represented the inter-relationship between low energy availability, menstrual function, and bone health, RED-S recognizes that the complications of low energy availability are more extensive, and that these complications are not just limited to female bodies.

RED-S re-establishes athlete health as the primary focus when it comes to fueling for optimal sport performance. Athletes and their coaches can become so focused on fueling for sport performance with pre-, intra-, and post-workout nutrition that fueling to maintain optimal health in the time between training and competition gets neglected. RED-S highlights the importance of fueling to support the functions required for optimal health first, since efforts to fuel specifically for sport performance will be counterproductive without having the body’s basic needs met.

RED-S Comes with Consequences for Athletic Performance

When an athlete doesn’t have adequate energy availability in the context of sport performance, the body is forced to adjust by reducing the energy allotted to support vital body systems and processes. This ultimately leads to a disruption in numerous hormonal, metabolic and functional processes. As a result of low energy availability, metabolic rate, menstrual function, bone health, immunity, protein synthesis, cardiovascular and psychological health can suffer.


Research shows that a decline in the above-mentioned body systems and processes can result in the following performance-related consequences for the athlete:

  • Decreased endurance performance
  • Increased injury risk
  • Decreased training response
  • Impaired judgment
  • Decreased coordination
  • Decreased glycogen stores
  • Decreased muscle strength

In addition, athletes who are affected by low energy availability may develop nutrient deficiencies including anemia, chronic fatigue and increased risk of infections and illnesses, all

of which have the potential to harm health and performance.

Low Energy Availability in Male Athletes

With the new focus on energy availability that RED-S brings to the forefront, it is now easier to see how this syndrome can be just as present in male athletes as it is in females, bringing new awareness to the hormonal health of males as well as the prevalence of disordered eating in this population that can lead to low energy availability.

Research shows that low energy availability occurs at a comparable rate in males and females. Not surprisingly, it seems that athletes competing in weight sensitive sports, regardless of gender, experience low energy availability at an increased rate compared to those who compete in sports where leanness is not as important for performance, appearance or requirement to meet a competition weight category.

Key Messages and Takeaways

  • Relative Energy Deficiency in Sport (RED-S) describes a condition of low energy availability in athletes who are inadequately nourished to support both athletic performance and general healthy functioning.
  • In a state of low energy availability, the body is forced to compensate by reducing the energy directed to support vital body systems and processes which is disruptive to numerous hormonal, metabolic and functional processes.
  • Low energy availability can negatively affect athletic performance including decreased endurance performance, increased injury risk, decreased training response, decreased glycogen stores, and decreased muscle strength.
  • RED-S brings new awareness to the hormonal health of males as well as the prevalence of disordered eating in this population which was previously overlooked by the Female Athlete Triad.


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. 2018;52:687–697.

Mountjoy M, Sundgot-Borgen J, Burke L, et al. The IOC consensus statement: beyond the Female Athlete Triad—Relative Energy Deficiency in Sport

(RED-S). Br J Sports Med. 2014;48:491–497.

Alida Iacobellis MHSc RD is the Owner of ALIVE Nutrition Solutions. She teaches athletes at all stages of their career how to stop wasting time and energy trying to keep up with the latest diet trends and start creating space for the things in life that really matter. She loves simplifying nutrition science into meaningful and realistic strategies you can apply to your day-to-day routine to create a thriving, vibrant, and happy life.

Avatar for Jerry Milani
Jerry Milani

Jerry Milani is a freelance writer and public relations executive living in Bloomfield, N.J. He has worked in P.R. for more than 25 years in college and conference sports media relations, two agencies and for the International Fight League, a team-based mixed martial arts league, and now is the PR manager for Wizard World, which runs pop culture and celebrity conventions across North America. Milani is also the play-by-play announcer for Caldwell University football and basketball broadcasts. He is a proud graduate of Fordham University and when not attending a Yankees, Rams or Cougars game can be reached at jerry (at) jerrymilani (dot) com.