Maintaining the health of the athlete can reduce days lost to injury and illness, extend seasons and careers and maximize performance.

As the Olympics reach a climax in Rio, it’s a certainty that many athletes are concerned about their energy balance. With back-to-back days of competition and the nutritional challenges faced by being away from home, it takes an extra level of awareness to stay on the positive side of the balance. Lending a hand to this awareness is the new popularity of the term RED-S.

RED-S stands for Relative Energy Deficiency in Sport, first introduced in 2014 by the International Olympic Committee (IOC). Understanding energy balance can help with the goal of attaining peak performance. Athletes know about it; coaches know about it – the question is what can they do about RED-S?

In simple terms, RED-S describes a state of energy deficiency in athletes, and its effect on many systems of the body which are integral to high-level sports performance (1).

It can afflict both men and women and covers a slew of physiological impairments. At its simplest, it’s a reflection on basic energy intake – not taking on board enough fuel to cover the energy used up in exercise and the energy needed for basic physiologic function.

Most people think that for female athletes this impairment is primarily focused on menstrual health and its effect on bone function. The original term, Female Athlete Triad (Triad), which covers the interactions between energy availability, menstrual function and bone health has evolved over the years.

But, importantly, RED-S differs in that it isn’t sex-specific, addressing that energy deficiency can impair the physiological function of both sexes.

RED-S does include the aspects of the Triad in its model but it covers much wider ground; energy deficiency may also impact the gastrointestinal, cardiovascular, immunologic, hematologic, and metabolic systems, may impair growth and development, and often includes psychological effects.

RED-S has significant impacts on performance. The bone impairment associated with hormonal imbalances caused by low energy availability can lead to stress fractures, and RED-S’ effects on the immune system may lead to increased risk of illness.

Some bone loss as a result of energy deficiency may be irreversible. Generalized performance effects are possible as well, including a decreased response to training and little improvement despite a heavy training load.

Though there has been less research in men, recent studies suggest they too can be negatively affected when energy restricted. Male athletes are at a lower risk of developing disordered eating and/or eating disorders than female athletes, but those in weight class sports, cycling, distance running, and other endurance activities are at risk for RED-S, stress fractures and low bone mineral density.

So, what do coaches look for in terms of signs and symptoms? RED-S isn’t a simple diagnosis, but assessing energy availability using a calculation involving energy intake, estimated energy expenditure and fat free mass is a good way to assess whether an athlete may have an issue with energy balance.

Weight loss, multiple stress fractures, as well as amenorrhea in female athletes are significant warning signs. In athletes with low energy availability, it’s important to work with them on increasing energy intake and/or reducing exercise and its intensity (2).

Kathryn E. Ackerman, MD, MPH is a sports medicine physician, endocrinologist,and the medical director of the Female Athlete Program in the Division of Sports Medicine at Boston Children’s Hospital. An Assistant Professor of Medicine at Harvard Medical School, she has presented locally and internationally about RED-S as well as other sports endocrine issues. Dr. Ackerman is a former national team lightweight rower, a team physician for US Rowing, and the course director for the Female Athlete Conference, held biennially in Boston.