What is RED‑S?
It often starts with a “good” habit that quietly goes too far. A young athlete decides to train harder to get faster, stronger or more competitive. Practices get longer, workouts get tougher, but their eating doesn’t keep up with the extra demand. Over time, their body is working with less fuel than it needs for training, recovery, and normal growth. That mismatch can lead to a condition called relative energy deficiency in sport, or RED‑S.
RED‑S describes a state where an athlete’s energy intake (food) is too low for their total energy expenditure (training, daily life, growth and development). When the body does not get enough energy to cover all of these needs, it begins to cut corners to survive. Systems that are not essential in the short term—like bone building, hormone production, immune defense and reproductive function—get dialed down so that basic life functions can continue.
The term RED‑S was introduced by an expert panel convened by the International Olympic Committee to expand on an older concept known as the “female athlete triad" where RED-S was thought to only have affected young female athletes. Today, we know this is not the case, both male and female athletes can be impacted by RED-S.
How RED‑S develops in young athletes
RED‑S recognizes that low energy availability affects many body systems, not just menstrual function or bone health, and that it can occur in both girls and boys. While research suggests that RED‑S may be more commonly identified in females, male athletes are also at risk, especially in sports that value leanness or have very high training volumes.
RED‑S can begin with:
Pressure from coaches, peers or social media to be leaner or “look the part” in certain sports.
Sports that emphasize low body weight, or endurance, such as distance running, gymnastics, dance, wrestling, cheer, figure skating or lightweight rowing.
Well‑meaning attempts to “eat clean,” cut out certain foods, or follow popular diets that are not appropriate for growing, highly active kids and teens.
Adolescents hear many nutrition messages that are marketed as “healthy” but don’t fit the needs of a developing, highly active body. A teen might reduce portion sizes, skip snacks, avoid carbohydrates or cut out entire food groups believing it will improve performance or appearance. At the same time, they may be adding practices, private lessons or strength sessions, dramatically increasing their energy needs without realizing it.
Many young athletes also struggle to translate abstract energy needs into real‑world eating. They may not recognize how much food is required to support both heavy training and normal growth. An eating disorder does not have to be present for RED‑S to develop, though underlying psychological factors such as perfectionism, anxiety, body image concerns or a strong desire to please others can increase vulnerability.
Regardless of the exact starting point, RED‑S can have serious short‑term and long‑term effects on health and performance in youth.
BONE HEALTH: Adolescence is a critical window for building strong bones. By about age 18, most teens have developed up to 90% of their peak bone mass. When a growing athlete consistently under‑fuels:
Hormonal systems that drive bone growth may slow down or shut off.
Diets may fall short in calcium, vitamin D and other nutrients needed for bone formation.
Bone mineral density can suffer, increasing the risk of stress reactions, stress fractures and, over time, early osteoporosis—fragile bones that are more likely to break.
If RED‑S persists during these key growth years, the body may never fully “catch up” to its genetic bone potential.
HORMONE HEALTH & REPRODUCTION:
In females, low energy availability can lead to:
Delayed onset of menstruation (primary amenorrhea) or Irregular or missed periods (secondary amenorrhea) in those already menstruating.
These changes are signs that estrogen levels are low, which is closely tied to bone health, cardiovascular health and overall well‑being.
In males, RED-S can lead to:
In males, RED‑S can show up as reduced sex hormones, lower libido and changes in growth and development, even if the signs are less obvious day to day.
Reduced gonadotropin‑releasing hormone (GnRH) from the hypothalamus, which can blunt luteinizing hormone (LH) and follicle‑stimulating hormone (FSH) pulses from the pituitary.
Shifts in metabolic hormones: lower leptin, insulin and triiodothyronine (T3), and higher cortisol, all of which signal “low fuel” and reinforce a lower‑energy state.
Case reports describe male endurance athletes (e.g., a Division I swimmer) with “strikingly low” total, free and bioavailable testosterone, with normal pituitary imaging and other labs, ultimately attributed to RED‑S; testosterone normalized after increasing intake and reducing training.
Reviews of male endurance athletes find that low energy availability correlates with reduced testosterone, lower resting metabolic rate and lower bone density.
RED‑S can quietly erode the very performance that athletes are working so hard to improve. Possible effects include:
Increased risk of injury, particularly bone stress injuries.
Decreased endurance and muscle strength.
Slower recovery after practices and competitions.
Reduced response to training—despite working harder, the athlete may stop improving or even regress.
Decreased coordination, slower reaction time and impaired judgment, all of which can affect performance and safety.
More frequent colds, infections or illnesses as immune function is compromised.
Increased irritability, mood swings, anxiety or depression.
Difficulty concentrating in school and increased fatigue throughout the day.
None of these outcomes align with an athlete’s goals—yet they can develop gradually, making them easy to miss until the problems become more serious.
PREVENTION: how parents can help
Parents and caregivers play a powerful role in reducing the risk of RED‑S. Some practical steps include:
Educate about fueling and growth. Help your child understand that intense training raises energy needs significantly and that proper nutrition supports bone health, hormone balance, recovery and injury prevention, not just body size.
Watch for warning signs. Pay attention to unexplained weight loss, stalled growth, delayed or changing menstrual patterns, persistent fatigue, mood changes, increased injuries, or a sudden shift toward rigid eating or body preoccupation.
Support regular eating. Encourage three balanced meals and one to three snacks daily. Even consistently missing a single meal—like skipping breakfast or not eating lunch at school—can create a meaningful energy deficit over time.
For many young athletes, the after‑school window is especially critical. They may go from lunch to practice without eating, leaving them under‑fueled for training. A simple, easily digested snack before practice can make a big difference. Examples include:
An energy bar or granola bar.
A bowl of cereal or a handful of crackers.
A banana or other fruit, with or without a small yogurt.
Pretzels or dry cereal mix.
A peanut butter and jelly sandwich.
Fruit juice or a smoothie alongside a small snack.
Creating a supportive environment where food is seen as fuel, not the enemy, can also reduce shame and secrecy around eating. Encourage open conversations about hunger, fatigue and body image, and help your athlete feel safe sharing concerns.
TREATMENT
The encouraging news is that RED‑S is treatable, and addressing it does not require giving up on athletic dreams. In fact, restoring adequate energy intake usually leads to better performance, not worse. Treatment often involves:
Increasing energy intake (more food, more often, with appropriate balance of carbohydrates, protein and fats). Work with a sports dietitian to help.
Sometimes adjusting training volume or intensity to allow the body to catch up.
Involving a multidisciplinary team, which may include a physician, a registered dietitian experienced in sports nutrition, and the coach or athletic trainer.
With early recognition and targeted support, most young athletes can return to full participation, build stronger bones, normalize hormones and feel better both on and off the field. The key is recognizing that health and performance go hand in hand—and that fueling the body properly is one of the most powerful training tools an athlete has.
