Relative energy deficiency affects your health and performance

As female athletes, we want to soar to our greatest potential. We have the discipline to follow demanding training schedules and are willing to sacrifice comfort for excellence. Thousands of hours are spent perfecting our skills: endurance, technique, power, speed. For some of us, food is a calculated part of our training, but all too often, we approach nutrition incorrectly.

Food is meant to fuel our bodies and bring joy. It is not something to be avoided or thought of only as a reward. Our bodies need it to function, and it is a critical ingredient for our athletic success. Athletes who do not get the fuel they need to train and perform can develop a syndrome called Relative Energy Deficiency in Sport (RED-S).

What is Relative Energy Deficiency in Sport?

RED-S describes the various health and performance consequences athletes may experience when their caloric intake from food is not adequate for normal body function. This low energy availability (LEA) is the cause of RED-S.

Energy Availability (EA)= Energy Intake (EI) (kcal) – Exercise Energy Expenditure (EEE) (kcal) / Fat Free Mass (FFM) (kg)

In this formula, EEE is the additional energy expended from exercise, above that which is expended by daily living.

Studies in women have suggested that an optimal EA may be around 45 kcal/kg FFM/day. An EA below 30 kcal/kg FFM/day may significantly disrupt the balance of various hormones in our bodies. These numbers, but each of us is likely to have her unique optimal EA for peak function and performance.

What are the different consequences of RED-S?

The potential health and performance consequences of RED-S are shown in the two figures. The International Olympic Committee (IOC) describes 10 health and 10 performance consequences in these illustrations, but there may be more. In female athletes, decades of research underpin what is called the “female athlete triad,” the combination of LEA, menstrual irregularity, and poor bone health. Today, we know that inadequate fueling causes menstrual dysfunction (missed cycles, infertility) and negatively impacts bone health, resulting in low bone density, stress injuries, and full fractures.

Health consequences of RED-S

More recently, other health effects of energy deficiency have become clear (e.g., thyroid dysfunction, cardiovascular effects, metabolism slowing, constipation, and diarrhea).

Furthermore, as RED-S continues, it inevitably affects athletic performance, causing increased injury rates, worse training recovery, reduced endurance performance, and difficulty concentrating.


Who is at risk for RED-S?

Any athlete of any gender, participating in any sport, is at risk for RED-S. RED-S is common among athletes in weight-category sports (e.g., boxing, lightweight rowing, taekwondo, wrestling), where there is a specific maximum weight that is allowed to compete in a certain weight class; aesthetic sports (e.g., dance, figure skating, gymnastics), where appearance and performance are subjectively judged; and endurance sports (e.g., cycling, running), where a lower body mass is often thought to improve speed.

However, athletes in any sport can purposefully or unintentionally underfuel. We recommend screening all athletes for RED-S. It is definitely worthwhile to take a closer look at your eating habits to determine if your nutrition is appropriate for your training.

Why is RED-S so common in athletes?

Many athletes develop RED-S because of messages they receive about body image. Coaches may make comments about “body types”. The media often portray female athletes as needing to emphasize their physical attractiveness. It is easy to feel the pressure to conform to a certain look when media seem to focus more on appearance than athletic achievement.

In addition, a lot of false information about the benefits of leanness for sports exists. An athlete may initially get faster or jump higher with some weight loss, but with prolonged or frequent energy deficiency, their health and performance suffer. The fastest runner on a high school team may be the thinnest, and she may inspire teammates to restrict their food intake to get faster, too. But, unfortunately, that top runner eventually has performance declines, injuries, and has to take big breaks from training and competing. She may need to drop out of the sport altogether. This is the aspect so many of her teammates may miss.

Potential performance consequences of RED-S

If I have RED-S, does it mean I have an eating disorder?

While some athletes with RED-S do have an eating disorder, many do not. You may develop low EA simply because you do not know how many calories you need to consume to support your exercise expenditure. For example, elite male rowers may need to consume over 10,000 calories per day to support their energy needs during high volumes of training. Even a growing adolescent female distance runner could require over 5000 calories per day. Such amounts can be surprising to athletes, and eating that amount of food can be quite daunting and time-consuming. Other athletes may not have access to enough food and suffer from food insecurity. Others are following specific diets, and their high fiber intake may decrease the absorption of nutrients. As you can see, there are many reasons why RED-S occurs.

How do I know if I have RED-S?

You should consider RED-S if you have noticed any changes in your health or performance. Have you felt more fatigued lately? Have you become more irritable or feel down? Are you working harder, but not seeing fitness gains? Are you getting preoccupied with food? There are various screening tools health professionals can use to help you figure out if you have RED-S. Some are eating disorder questionnaires or overtraining checklists. It is also important to rule out other causes of your symptoms. The RED-S clinical assessment tool (RED-S CAT) was developed by the IOC to screen for signs and symptoms of RED-S.

It is important that you discuss your symptoms with a health professional.

How do I get treated for RED-S?

Interdisciplinary teams work best. Working with a doctor, a registered dietitian, and a psychotherapist, all experienced with RED-S, can be really beneficial. The doctor can help assess you for RED-S while investing other medical issues or consequences. They may order further labs (blood and/or urine tests) or imaging, such as a bone density scan (dual-energy x-ray absorptiometry, or DXA). The results can help guide your treatment.

The dietitian can review your training and your eating behaviors to see where you may need to make adjustments. They may give you specific advice about how and where to make gradual changes. The therapist can help you process all the information and approach your eating in a different way, optimizing your fueling for improved mental and physical health, as well as performance. Ideally, the more supportive members you have on your treatment team, the better. Coaches, athletic trainers, teammates, and family members can all be incorporated in the right context.

How can I help protect myself and others from RED-S?

Talk about it! More and more athletes are coming forward with their struggles with RED-S. Don’t be ashamed. Normalize the conversation and help steer people towards resources. ShePowerSport is a great one.

Here are some others:


Mountjoy M, Sundgot-Borgen J, Burke L, Carter S, Constantini N, Lebrun C, Meyer N, Sherman R, Steffen K, Budgett R, Ljungqvist A, Ackerman K. The IOC relative energy deficiency in sport clinical assessment tool (RED-S CAT). Br J Sports Med. 2015 Nov;49(21):1354.

Ackerman KE, Stellingwerff T, Elliott-Sale KJ, Baltzell A, Cain M, Goucher K, Fleshman L, Mountjoy ML. #REDS (Relative Energy Deficiency in Sport): time for a revolution in sports culture and systems to improve athlete health and performance. Br J Sports Med. 2020 Apr;54(7):369-370.



  • I am internist, sports medicine doctor, and endocrinologist. I represented the US as a lightweight rower and am a current team physician for US Rowing. I am an assistant professor at Harvard Medical School and the founder and director of the Female Athlete Program at Boston Children’s Hospital, where we treat female athletes of all ages. I am also the director of our biennial Female Athlete Conference, which brings together researchers, coaches, medical professionals and athletes to improve the knowledge about optimizing female athlete health and performance. I love helping female athletes reach their full potential.