Relative Energy Deficiency in Sport: More Than Missed Periods
She may be a high school runner whose periods have become increasingly irregular.
A collegiate athlete who has not menstruated in a year but has been told this is “normal for athletes.”
A recreational cyclist in her 30s who trains before work, eats what appears to be a healthy diet, and cannot understand why she is exhausted, cold, irritable, and repeatedly injured.
Or a woman who has been praised for her discipline, her leanness, and her commitment, while her body has been quietly shutting down functions it no longer has enough energy to support.
These patients do not always look unwell. They may be strong, fast, high-performing, and intensely motivated. Their weight may fall within a “normal” range. They may not have an eating disorder. Most are not intentionally restricting food at all.
But their bodies are receiving the same message:
There is not enough energy available to do everything being asked of me.
That is the central problem in Relative Energy Deficiency in Sport, now generally abbreviated REDs.
REDs can affect athletes of any sex, age, body size, or competitive level. But for girls and women, a changing or disappearing menstrual cycle can provide an especially important warning sign.
A lost period is not evidence that the body has become exceptionally fit. It may be a sign that the body does not have enough available energy to support normal reproductive function.
What is REDs?
REDs is a syndrome caused by problematic low energy availability.
Energy availability is not simply the number of calories a person eats. It refers to the energy remaining after the demands of exercise have been subtracted—the energy the body still has available to support everything else it needs to do.
That includes:
maintaining bone
producing hormones
regulating body temperature
supporting immunity
building and repairing muscle
making blood cells
maintaining cardiovascular and gastrointestinal function
supporting concentration, mood, and sleep
allowing normal growth and reproduction
When exercise demands rise without a sufficient increase in food intake, or when intake falls while training remains high, the body begins making trade-offs.
Human physiology is remarkably adaptive. During short periods of energy scarcity, the body can conserve energy and prioritize immediate survival. But when the mismatch becomes prolonged, severe, or recurrent, those adaptations can become harmful.
The 2023 International Olympic Committee consensus defines REDs as impaired physiological or psychological functioning caused by prolonged or severe low energy availability. Its effects can extend across reproductive, skeletal, metabolic, cardiovascular, hematologic, immune, gastrointestinal, and psychological health, and can ultimately impair athletic performance as well.
This is why REDs is much larger than the menstrual cycle. The absent period may be the visible clue. The energy deficiency is the underlying problem.
REDs is not limited to elite or underweight athletes
The word “sport” can make REDs sound like a condition confined to Olympians, professional dancers, or ultramarathoners.
It is not.
I think of an athlete broadly as anyone whose regular physical activity meaningfully affects her energy needs. That may include a competitive gymnast or distance runner, but it may also include a teenager playing multiple school sports, a recreational triathlete, a dancer, a military service member, or a woman combining daily exercise with a demanding job and a tightly controlled diet.
REDs can occur at any body size. A person can be weight-stable and still have inadequate energy available for normal physiology because the body has reduced its metabolic output to compensate. It can also happen without deliberate restriction.
Some athletes underestimate how much fuel their training requires. Others become busy and miss meals. Some eat large amounts of high-fiber, low-energy-density foods and feel physically full before meeting their needs. Exercise may blunt appetite. Gastrointestinal symptoms can make eating difficult. Food insecurity may play a role.
And many athletes have absorbed a cultural message that eating less, weighing less, or becoming leaner will always improve performance.
The IOC prevention review emphasizes that low energy availability can arise intentionally or unintentionally: from dietary restriction, limited nutrition knowledge, lack of time, low-energy-density diets, food insecurity, exercise-related appetite changes, or a sudden increase in training volume. It also specifically calls for less emphasis on weight and leanness, especially in young athletes.
The menstrual cycle is a vital sign
When the brain perceives that energy availability is inadequate, it may reduce the signaling needed for normal ovulation and ovarian hormone production.
The result can be functional hypothalamic amenorrhea: a reversible suppression of the reproductive system caused by insufficient energy availability, physiological stress, psychological stress, or some combination of these factors.
Periods may become further apart, lighter, or unpredictable before disappearing completely. Ovulation can also become inconsistent even when some bleeding continues.
This is not menopause, and it is not the same as primary ovarian insufficiency.
In primary ovarian insufficiency, the ovary itself is no longer functioning normally. In REDs, the ovaries may be capable of functioning, but the brain has reduced the hormonal signal telling them to do so.
That distinction matters because the central treatment is different.
But the low-estrogen state can still matter enormously.
A teenager or young woman with functional hypothalamic amenorrhea may spend months or years with estrogen levels that are inadequate for her stage of life. During adolescence and young adulthood, when the body should be building peak bone mass, she may instead be losing an irreplaceable window for bone development.
This is one reason I believe REDs belongs in the broader conversation about early estrogen loss.
The mechanism is different from surgical menopause or primary ovarian insufficiency. The condition may be reversible. But a young body is still being deprived of the hormonal environment it should have, and the consequences should not be minimized.
“Athletes don’t get periods” is not acceptable medical advice
For generations, menstrual loss was normalized in female athletes.
It was viewed as an expected consequence of serious training, a sign that someone was working hard enough, or even a competitive advantage.
It is none of those things. It is a clinical finding that deserves an explanation.
Not every menstrual irregularity in an athlete is caused by REDs. Pregnancy, polycystic ovary syndrome, thyroid disease, elevated prolactin, primary ovarian insufficiency, medications, uterine conditions, and other causes must be considered.
But “you exercise a lot” should not end the evaluation.
And placing a patient on a birth control pill solely to manufacture predictable bleeding does not establish that the underlying problem has been resolved.
Combined hormonal contraception can create a scheduled withdrawal bleed while suppressing the patient’s natural reproductive hormones. That may obscure whether spontaneous ovulation and menstruation have recovered. It may provide contraception or help with other symptoms, but it should not be mistaken for proof that energy availability is now adequate.
What else can REDs look like?
One reason REDs is missed is that no single symptom defines it.
Some athletes lose their periods. Others continue bleeding but develop injuries, fatigue, or declining performance. Hormonal contraception may conceal menstrual changes altogether.
Possible clues include:
irregular or absent periods
delayed onset of menstruation in an adolescent
recurrent bone stress injuries or fractures
declining bone density
persistent fatigue
feeling unusually cold
poor recovery from training
declining strength, endurance, or performance
repeated illness
iron deficiency or other hematologic abnormalities
difficulty concentrating
irritability, anxiety, low mood, or disrupted sleep
low libido
gastrointestinal symptoms
unexplained weight loss—or failure to grow as expected
rigid food rules or fear of increasing intake
compulsive exercise
a plateau despite training harder
The endocrine effects can extend beyond estrogen. Energy deficiency may alter thyroid signaling, growth hormone pathways, cortisol regulation, leptin, insulin, and other systems involved in metabolism and reproduction. The Endocrine Society review describes REDs as a multisystem condition involving reproductive, thyroid, adrenal, growth-related, bone, hematologic, immune, gastrointestinal, neuromuscular, and psychological abnormalities.
The athlete may interpret these changes as evidence that she needs to become even more disciplined.
She feels slower, so she trains harder.
Her body composition changes, so she restricts more.
She becomes injured and replaces running with another form of exercise rather than resting.
She loses her period and assumes that is simply what serious athletes do.
The very symptoms showing that the body needs more support can drive behaviors that deepen the energy deficit.
REDs can undermine the performance an athlete is trying to protect
Athletes are often reluctant to change their nutrition or training because they fear losing fitness, changing their bodies, or falling behind.
That fear deserves to be taken seriously. But prolonged underfueling is not a reliable performance strategy.
A body without enough energy may struggle to replenish glycogen, synthesize muscle, recover from training, maintain concentration, or build bone. The athlete may initially become lighter or see a temporary improvement in power-to-weight ratio, but that does not mean the strategy is sustainable.
Eventually, performance may plateau or decline. Injuries accumulate. Training consistency suffers. Strength and endurance deteriorate. Illness interrupts competition. The athlete works harder and gets less from the work.
More training is not always more productive training. Training only creates adaptation when the body has enough fuel and recovery to respond to it.
How is REDs diagnosed?
There is no single blood test that confirms REDs.
There is also no one calorie threshold, body-fat percentage, or menstrual pattern that applies to every athlete.
Diagnosis requires assembling the full clinical picture: nutrition, training, menstrual and reproductive history, injuries, growth, bone health, mental health, medications, performance changes, physical findings, and laboratory or imaging results when appropriate.
The IOC’s REDs Clinical Assessment Tool, version 2, uses a three-step framework:
Initial screening through validated questionnaires or clinical interviewing
Assessment of signs, symptoms, and health risks
A physician-led diagnosis and individualized treatment plan, ideally developed with a multidisciplinary team
The tool stratifies severity using green, yellow, orange, and red categories and links those categories to recommendations about training and competition. It is intended to support but not replace clinical judgment, and other causes of each abnormal finding still need to be excluded.
Depending on the patient, evaluation may include:
a detailed menstrual history
pregnancy testing
thyroid and prolactin testing
reproductive hormone testing when clinically useful
complete blood count and iron studies
metabolic testing
vitamin D or other nutritional assessment
evaluation for disordered eating or an eating disorder
bone-density testing
imaging for suspected bone stress injury
assessment of cardiovascular signs or severe metabolic suppression
A “normal” body mass index does not rule REDs out.
Neither does a single normal estradiol, FSH, thyroid, or metabolic result.
The treatment is not simply “eat more”
At its core, treatment requires correcting the energy mismatch.
That may mean increasing total intake, improving the timing of nutrition around training, reducing exercise expenditure, or a combination of doing both.
But telling an athlete to “eat more” is often no more useful than telling someone with insomnia to “sleep more.”
A meaningful plan may require addressing:
how much energy the athlete actually needs
carbohydrate availability before, during, and after training
adequate protein and dietary fat
meal and snack timing
long gaps without food
early-morning fasted training
fear of specific foods
gastrointestinal symptoms
food access and practical constraints
compulsive exercise
body-image distress
coaching or team pressures
whether the current training load is medically safe
The best care is often multidisciplinary. Depending on the situation, that may include a physician, sports dietitian, mental health professional, athletic trainer, physical therapist, coach, and family.
What is the role of hormone treatment?
This is where the conversation becomes a little more nuanced.
The most important treatment for REDs is correcting the underlying energy deficit. Hormones cannot replace the calories, carbohydrates, nutrients, and recovery the body needs. Neither hormone therapy nor a combined hormonal contraceptive should be used as a way to continue underfueling without addressing the root cause.
At the same time, prolonged estrogen deficiency matters, especially during adolescence and young adulthood, when the body should still be building peak bone mass. If periods do not return despite meaningful changes in nutrition and training, or if bone density is already low, adding hormonal treatment may be appropriate.
There are two main options: physiologic hormone therapy, typically using transdermal estradiol with progesterone or progestin when the uterus is present, or a combined hormonal contraceptive such as the birth control pill, patch, or ring.
The best choice depends on the individual patient and her goals.
A combined hormonal contraceptive provides reliable pregnancy prevention and may also help with bleeding or other gynecologic concerns. However, the scheduled bleeding it produces does not mean that the athlete’s natural menstrual cycle has recovered, and it can make it harder to know whether the underlying energy deficiency has improved.
Hormone therapy does not provide contraception. Some research suggests that transdermal estradiol may be more helpful for bone density than a traditional birth control pill in athletes with absent or infrequent periods. However, we do not have enough evidence to say that one approach is best for every patient.
For a patient who needs or wants reliable pregnancy prevention, a combined hormonal contraceptive may be the most practical choice. For someone whose main concern is bone protection and who does not need contraception, physiologic hormone therapy may be preferred. There are other options including a progestin IUD for contraception paired with transdermal estradiol. This should be a shared decision based on bone health, bleeding preferences, medical history, pregnancy-prevention needs, and the patient’s priorities.
Most importantly, replacing estrogen does not treat the full REDs syndrome.
Low energy availability affects much more than the ovaries. It can alter cortisol, thyroid signaling, leptin, insulin, growth hormone pathways, metabolism, and blood-vessel function. Estrogen may help address one important consequence of REDs, but it does not automatically reverse the broader hormonal and metabolic changes caused by chronic underfueling.
Early research has also found signs of impaired blood-vessel function in some young women with functional hypothalamic amenorrhea. This raises concern that prolonged low energy availability may affect future cardiovascular health in ways that are not fully corrected by replacing estrogen alone. We still need more long-term research before we can say exactly how much this changes a woman’s lifetime cardiovascular risk.
The takeaway is not that hormone treatment is unhelpful. It can be an important part of care. But it is only one part. The goal is not simply to create monthly bleeding or normalize an estradiol level. The goal is to restore adequate fueling, protect bone and cardiovascular health, support recovery, and help the athlete return to sustainable health and performance.
Prevention cannot rest entirely on the athlete
Prevention means:
teaching athletes that menstruation is a health marker
providing realistic education about fueling requirements
responding promptly to menstrual changes and bone injuries
limiting unnecessary body-composition testing
keeping weight and body-composition data confidential
avoiding casual comments about an athlete’s size or shape
refusing to celebrate weight loss without understanding its cause
building access to sports dietitians and qualified medical care
creating a culture in which rest and recovery are part of training
The IOC prevention framework makes the same point: preventing REDs requires action from the entire athlete ecosystem, not simply more responsibility placed on the individual athlete.
Why I am writing about REDs
My work includes caring for women who lose estrogen earlier than expected.
Some lose ovarian function because of surgery, chemotherapy, radiation, primary ovarian insufficiency, or medications used to treat cancer.
Women with REDs arrive at low estrogen through a different pathway. Their ovaries have not necessarily failed. Their brain and body have adapted to an environment in which there is not enough energy available to support reproduction.
But the experience can still be profound. And it asks us to offer young athletes something better than the false choice between health and performance.
With the right support, those goals should reinforce each other.
A healthy body is not an obstacle to athletic performance. It is the foundation of it.
