Relative Energy Deficiency in Sport (RED-S)
BLACK IRON RADIO EP. 329: Relative Energy Deficiency in Sport (RED-S)
Relative Energy Deficiency in Sport (RED-S) is what happens when an athlete's energy intake doesn't match the demands of their training and life. It's not just about missing periods or being "too lean." Chronic low energy availability can suppress hormones, reduce bone mineral density, alter thyroid function, impair recovery, and decrease performance. What was once labeled the Female Athlete Triad was expanded in 2014 to reflect what research made clear: this affects all genders and multiple physiological systems.
Lauren, Amanda, and Krissy unpack how RED-S develops over time, why it's easy to normalize in competitive environments, and the patterns coaches and athletes should be paying attention to. They discuss weight-class and aesthetic sports, repeated fat loss phases, carbohydrate availability, stress load, and how to align nutrition with training cycles without compromising long-term health. If you care about performance that lasts, this conversation is foundational.
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Note: This post discusses topics related to disordered eating and energy restriction. Please read with care.
Energy deficit in sport is such a common problem it has a name. Relative Energy Deficiency in Sport, or RED-S, describes a syndrome of declining health and athletic performance that happens when athletes don't get enough food to support the energy demands of their daily lives and training. It can and does affect athletes of any gender and ability level.
In a recent episode of Black Iron Radio, coaches Lauren (certified nutrition specialist and licensed nutritionist) and Amanda (athlete and nutrition coach with personal experience with RED-S) joined host Krissy to break down what RED-S actually is, why we're seeing more of it, and what athletes and coaches can do about it.
First, Let's Clear Up What RED-S Is Not
Before diving in, it helps to understand what RED-S is not:
It is not an eating disorder. RED-S can be associated with disordered eating, and someone with RED-S may also have an eating disorder, but they are not the same thing. RED-S is not classified in the DSM-5 (the Diagnostic and Statistical Manual of Mental Disorders, which is the standard reference used by clinicians to diagnose mental health and psychiatric conditions).
It is not a willpower or discipline issue. Sometimes falling into RED-S is completely unintentional. It can stem from coaching advice, information found online, or training practices an athlete genuinely believes are helping their performance.
It is not something that happens overnight. RED-S develops over months or years. Nutrient depletion is slow. Bone density loss is slow. Hormonal disruption is slow. Your body doesn't just wake up one day with RED-S.
A Brief History
RED-S was originally known as the Female Athlete Triad, a term that emerged in the 1990s when the condition was first identified in female athletes. It was characterized by three features: disordered eating, low bone density, and irregular periods or amenorrhea.
In 2007, the concept was broadened to include anyone with chronically low energy availability (LEA), regardless of gender. And in 2014, the International Olympic Committee introduced the RED-S framework to make it more inclusive and to reflect the full scope of what chronic underfueling actually does to the body.
The shift mattered because low energy availability doesn't just affect the reproductive system. It affects nearly every system in the body.
What Low Energy Availability Actually Does
When an athlete consistently doesn't eat enough to support their training and daily life, LEA produces several hormonal and metabolic changes::
Decreased metabolic rate
Decreased production of sex hormones
Slower bone rebuilding and faster bone loss, increasing fracture risk
Decreased protein synthesis, making it harder to build or retain lean mass
Impaired cardiovascular health and performance
Gastrointestinal issues, including dietary intolerances
Compromised immune function, including chronic autoimmune conditions
Psychological effects including anxiety and depression
Impaired growth and development
If an athlete continues to push without eating enough, the energy deficit compounds and the health consequences become more serious.
How to Recognize It
RED-S is a spectrum condition. You can't diagnose it with a single lab test or diagnostic tool. It presents differently in everyone, and symptoms in isolation might not feel alarming at all. In athletic populations especially, feeling run down gets normalized fast.
For individuals who should be menstruating, RED-S often shows up in the reproductive system first:
Primary amenorrhea: not getting a period by age 16
Secondary amenorrhea: losing a period for three or more months
Oligomenorrhea: infrequent periods, often 35 or more days apart
Other symptoms that can affect any athlete include:
Lethargy and fatigue
Frequent illness
Depression, irritability, lack of motivation, or mood swings
Changes in body composition, specifically loss of lean mass including bone
Trouble regulating body temperature
Sexual dysfunction
Hair loss
In men specifically, testosterone can drop significantly
One thing that makes RED-S especially tricky to self-identify is that if everyone around you is eating and training the same way, the symptoms start to feel like the baseline. That's part of why environments like competitive running, gymnastics, or figure skating can have high concentrations of RED-S. When the behavior is normalized by the group, no one questions it.
Why We're Seeing More of It
More people are participating in sport than ever before, from recreational to competitive levels. Community-based sports, social media, aesthetic pressures, and the culture of "who's tougher" all create conditions where underfueling gets rewarded or goes unnoticed. And frankly, we're just beginning to understand the long-term effects of chronic low energy availability across different life stages and populations.
The Long-Term Stakes
This is worth pausing on, especially for younger athletes. Peak bone mass for females is reached in the early twenties. For males, it's the mid to late twenties. After that, everyone faces the same rate of bone loss. If you enter that phase with impaired bone mineral density because of chronic underfueling during your developmental years, you're starting from a disadvantaged position that doesn't go away.
Osteoporosis is a leading cause of death in older adults. The degree to which you lose bone mass affects your quality of life, your autonomy, how much care you need. What you do now matters later.
RED-S is not a death sentence. You can improve the situation, especially if you're willing to make some changes early on when you're noticing symptoms.
What This Means for Coaches
RED-S tends to show up more in sports where image matters (gymnastics, figure skating, bodybuilding) and in weight class sports (weightlifting, powerlifting, strongman, combat sports). But it can happen in any sport, at any ability level. Don't let sport type be your only filter.
A few things to keep in mind when working with athletes:
The more restrictive an athlete's diet, the higher their risk for LEA. Watch for within-day deficits too, not just overall calorie totals. Timing and distribution of food intake matters, especially for endurance athletes at high training volumes.
Encourage avoiding comparison to what other athletes are or aren't eating. What someone posts online tells you nothing about whether their choices are actually supporting their health.
If symptoms are present, a temporary dial-back in training volume may be necessary with the goal of getting back to sport at a higher level of health.
Multimodal care is sometimes needed. Nutrition alone isn't always enough. Mental health support, sports medicine, and other specialists may need to be part of the picture.
If an Athlete Wants to Lose Weight or Change Body Composition
There is a right time and a wrong time for a fat loss phase, and there are more wrong times than right ones.
Before going into any kind of deficit, an athlete should have a consistent menstrual cycle (if applicable), labs that show hormones, nutrients, and other markers are within healthy ranges, and a manageable overall stress load. High life stress combined with training stress combined with a calorie deficit is a recipe for problems.
Fat loss phases should not happen during peak season. Save major nutritional adjustments for the off-season.
If an athlete is in a weight class or physique sport, regular breaks from dieting are essential. These breaks allow the body to return to baseline, support recovery, build strength, and provide a mental reset. They also help maintain metabolic flexibility, which makes future body composition changes easier.
Ask why. If an athlete comes to you wanting to lose fat, understanding the reason matters. Is it performance-based? Is it rooted in comparison to other athletes? Is the goal actually realistic and healthy for that person's body? These are important conversations to have.
And remember: the body has a long memory. The more often and more extreme the calorie restriction, the harder subsequent fat loss phases tend to be. A gradual, communicative approach is always the better long-term strategy.
When You Suspect RED-S Is Already Present
If a client is inadvertently losing weight, showing signs of low energy availability, or you suspect RED-S may be a factor, here's how to approach it:
Start observational. Have athletes track their energy levels, mood, motivation, cycle regularity, training performance, and recovery. This data is useful and it builds self-awareness without being prescriptive or triggering.
Watch the carbs. Athletes with food fears often reach for "safe" foods like fruits and vegetables when told to eat more. But excess fiber isn't a usable energy source, it creates satiety, and it can actually impair nutrient absorption and estrogen reabsorption, which affects menstrual cycle regulation. When increasing calorie and carbohydrate intake, the goal is not to also increase fiber.
Don't make macro tracking mandatory. For some athletes, tracking macros helps ensure they're eating enough. For others, it triggers obsessive or restrictive behaviors. Use it as a tool where it helps, and lean into more intuitive approaches where it doesn't. The goal is knowing whether someone is eating enough, not hitting a precise number.
Meet them where they are. Restricting energy intake may be the only way of eating a client has ever known. Compassion and patience matter here. Don't lecture. Explore. Review their training and eating plan with them and look for patterns.
Refer out when needed. Tools like the LEAF-Q questionnaire can help identify LEA in a clinical setting. If labs, DEXA scan results, or symptoms suggest RED-S, refer to a GP first, who can then direct the athlete to a sports medicine doctor, endocrinologist, or other specialist as appropriate.
The Bottom Line
RED-S is not a moral failure. It's not about discipline or toughness. It's a medical condition with a name, a framework, and a treatment path. The fact that it has a classification means the medical community can help diagnose and address it. It's not on you to figure out alone.
Think of it like any other injury. You may need to stop or scale back the thing you love for a while. But the goal is always to come back to it healthier, stronger, and with a fueling approach that actually supports your body for the long haul.
There's life after athletics. Fuel like it.
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If you enjoyed this conversation, check out more episodes of Black Iron Radio, where we cut through the noise and give you real, no-BS advice on feeling, performing, and looking your best. Each week we share practical nutrition, training, and wellness strategies and tips to help you succeed.
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