When athletes hear the term RED-S (Relative Energy Deficiency in Sport), many assume it is a diagnosis that suddenly appears.
In reality, RED-S develops gradually.
It is usually the result of a process that begins much earlier:
Underfueling → Low Energy Availability (LEA) → Relative Energy Deficiency in Sport (RED-S)
Understanding this pathway is one of the most important steps athletes, coaches and parents can take to protect both performance and long-term health.
The International Olympic Committee (IOC) introduced the concept of RED-S in 2014, replacing the narrower focus of the Female Athlete Triad. The IOC recognised that energy deficiency affects athletes of all sexes, ages, body sizes and sporting disciplines, with consequences extending far beyond menstrual health and bone density.
The IOC updated its consensus statements in 2018 and 2023 as research continued to show how complex and widespread the effects of low energy availability can be.
What Is Energy Availability?
Before understanding RED-S, it is important to understand Energy Availability (EA).
Energy availability describes the amount of energy left for your body’s normal physiological functions after the energy cost of exercise has been removed.
In simple terms:
Energy Availability = Energy Intake − Exercise Energy Expenditure
Your body requires energy every second of every day — not just when you train.
Even while sleeping, your body is using energy to:
- Keep your heart beating
- Power your brain
- Support breathing
- Maintain body temperature
- Produce hormones
- Repair muscles
- Build and maintain bone
- Support immune function
- Digest food
- Regulate metabolism
- Maintain reproductive function
- Support growth and development
Exercise is simply an additional demand placed on your body.
If there is not enough energy remaining after training, the body has to decide where to conserve energy.
This is where problems can begin.
Energy Availability Is Not About BMI, Weight or Appearance
One of the biggest misconceptions about RED-S is that it only affects athletes who look thin.
This is not true.
Energy availability is not determined by:
- Body weight
- BMI
- Body fat percentage
- Appearance
It is determined by whether enough energy remains to support normal physiological function after exercise demands have been met.
An athlete can:
- Have a “healthy” BMI
- Look muscular
- Maintain their weight
- Gain weight
and still experience Low Energy Availability (LEA).
RED-S cannot be diagnosed simply by looking at someone.
The important question is not:
“What do I weigh?”
It is:
“Am I eating enough to support everything my body is being asked to do?”
Energy Availability Changes Throughout Life
Many athletes assume they have one calorie requirement that stays the same year-round.
In reality, energy needs constantly change.
Both sides of the equation fluctuate:
Energy intake changes.
Exercise demands change.
Physiological requirements change.
Your body may require significantly more energy during:
- Heavy training blocks
- Marathon preparation
- Competition season
- Injury rehabilitation
- Illness
- Growth and puberty
- Muscle-building phases
- Pregnancy and breastfeeding
- Periods of high stress
- Extreme environments such as heat or cold
If food intake does not increase alongside these demands, energy availability decreases.
Stage One: Underfueling
What Is Underfueling?
Underfueling is the behaviour of consuming less energy than your body requires.
It can happen intentionally or unintentionally.
Intentional Underfueling
Some athletes restrict food because they:
- Want to lose weight
- Believe lighter is faster
- Are chasing a certain physique
- Follow restrictive diets
- Remove carbohydrates
- Skip meals
- Experience disordered eating
Unintentional Underfueling
This is often more common.
Athletes may underfuel because:
- Training increases but food intake stays the same
- They underestimate their energy requirements
- They are busy with work, university or travel
- Appetite decreases after exercise
- Gastrointestinal symptoms make eating difficult
- Food access is limited
- They have never been taught how to fuel properly
Many athletes genuinely believe they are eating “healthy” while still not eating enough to support their training.
Who Is at Risk?
According to the IOC, anyone participating in sport or regular exercise can develop RED-S.
This includes:
- Elite athletes
- Recreational athletes
- Children
- Adolescents
- Adults
- Masters athletes
- Female athletes
- Male athletes
- Para athletes
Risk may be increased in sports that emphasise:
- Leanness
- Appearance
- Weight categories
- Endurance performance
Including:
- Running
- Cycling
- Triathlon
- Dance
- Gymnastics
- Figure skating
- Rowing
- Combat sports
However, RED-S can occur across all sports, including team sports, strength sports and recreational exercise.
How Can Athletes Avoid Underfueling?
Practical strategies include:
- Eat consistently throughout the day
- Increase intake when training increases
- Do not fear carbohydrates
- Fuel before longer sessions
- Refuel after training
- Carry portable snacks
- Avoid skipping meals because you are “not hungry”
- Plan nutrition as carefully as training
- Remember recovery nutrition is part of training
Food is not separate from performance.
Food is part of performance.
Stage Two: Low Energy Availability (LEA)
Underfueling is the behaviour.
Low Energy Availability (LEA) is the physiological consequence.
LEA occurs when there is not enough energy remaining after exercise to support normal body functions.
The body responds by conserving energy.
It begins reducing energy available for systems that are important for long-term health and performance, including:
- Hormone production
- Bone formation
- Muscle protein synthesis
- Recovery and adaptation
- Immune function
- Growth
- Reproduction
- Metabolic regulation
Initially, these changes may not be obvious.
Many athletes continue training while their body is already struggling to adapt.
Early Warning Signs of LEA
Common symptoms include:
- Persistent fatigue
- Declining performance
- Poor recovery
- Increased muscle soreness
- Frequent illness
- Feeling cold
- Sleep disturbances
- Digestive problems
- Hair thinning
- Reduced concentration
- Mood changes
- Irritability
- Reduced motivation
Female athletes may experience:
- Irregular menstrual cycles
- Missing periods
- Delayed puberty
Male athletes may experience:
- Reduced libido
- Fewer morning erections
- Symptoms associated with lower testosterone
What Does the Research Show?
Recent research in male athletes found that athletes with indicators of low energy availability were:
- 2.9 times more likely to report cardiovascular dysfunction
- 3.2 times more likely to report psychological illness
- 2.6 times more likely to experience reduced training response
- 2.3 times more likely to report reduced endurance performance
The same research identified associations between low energy availability and increased:
- Immune disturbances
- Metabolic disruption
- Gastrointestinal issues
- Psychological symptoms
This reinforces that RED-S affects males as well as females and extends far beyond reproductive health.
Research in national athletes has also linked LEA with:
- Lower testosterone
- Lower estradiol
- Lower thyroid hormone (fT3)
- Lower reproductive hormones
- Lower ferritin
- Reduced bone mineral density
Stage Three: Relative Energy Deficiency in Sport (RED-S)
When LEA becomes prolonged, athletes may develop Relative Energy Deficiency in Sport (RED-S).
RED-S is not one single condition.
It is a syndrome affecting multiple body systems.
The IOC defines RED-S as impaired physiological and psychological functioning caused by problematic low energy availability.
Health Consequences of RED-S
RED-S may affect:
- Hormonal function
- Bone health
- Cardiovascular health
- Gastrointestinal function
- Immune function
- Metabolic function
- Growth and development
- Reproductive health
- Psychological health
- Haematological health
- Musculoskeletal health
Performance Consequences of RED-S
Athletes with RED-S may experience:
- Reduced endurance
- Reduced strength
- Poor recovery
- Reduced training adaptation
- Reduced coordination
- Reduced concentration
- Increased injury risk
- Increased illness
- Reduced glycogen stores
- Lower motivation
- Poor competition performance
Can You Have RED-S Without Losing Weight?
Yes.
This is one of the biggest misconceptions.
Many athletes with RED-S:
- Maintain their weight
- Have a “normal” body size
- Even gain weight
RED-S is about energy availability, not body size.
You cannot diagnose or exclude RED-S simply by looking at someone.
RED-S Across the Lifespan
Children
Children require energy for:
- Growth
- Brain development
- Bone development
- Sport
Warning signs may include:
- Poor growth
- Delayed development
- Frequent injuries
- Constant fatigue
Adolescents
Adolescence is one of the highest-risk periods.
Athletes are managing:
- Rapid growth
- Puberty
- Hormonal changes
- Increasing training loads
- Body image pressures
Warning signs include:
- Delayed puberty
- Missing periods
- Stress fractures
- Mood changes
- Falling performance
Adults
Many adult athletes unintentionally underfuel because life becomes busy.
Training increases, but eating habits often remain unchanged.
Planning nutrition around training becomes essential.
Masters Athletes
Energy remains critical as athletes age.
Underfueling may contribute to:
- Muscle loss
- Reduced bone density
- Slower recovery
- Increased injury risk
What Coaches Can Do
Coaches are often the first people to notice changes.
They can help by:
- Creating a food-positive culture
- Avoiding body-focused comments
- Encouraging recovery nutrition
- Supporting conversations around menstrual health
- Recognising repeated injuries and illness
- Referring athletes for professional support
What Parents Can Do
Parents can support young athletes by:
- Encouraging regular meals
- Providing snacks around training
- Avoiding “good” and “bad” food labels
- Monitoring changes in mood, energy and recovery
- Taking menstrual changes seriously
- Seeking advice early
What Athletes Should Remember
Food is training.
Recovery begins with your next meal.
Carbohydrates are essential for performance.
Rest is productive.
Health always comes before performance.
The Take-Home Message
The pathway is simple:
Underfueling is the behaviour.
Low Energy Availability (LEA) is the physiological state.
Relative Energy Deficiency in Sport (RED-S) is the syndrome that can develop when LEA continues.
The earlier underfueling is recognised, the easier it is to address.
Performance should never come at the expense of health.
The best-performing athletes are not those who eat the least.
They are the athletes who consistently provide their bodies with enough energy to:
- Train
- Recover
- Adapt
- Perform
- Thrive
Why RED-SCUE Was Created
Low energy availability does not happen overnight.
It can come from small daily gaps between what you eat and what your body needs.
Over time, underfueling can affect:
→ Performance
→ Recovery
→ Hormones
→ Bone health
→ Immunity
→ Training consistency
That is why RED-SCUE was created.
Carbohydrate-first fuel built for athletes.
Made with whole-food carbohydrate sources like cassava and plantain fufu, providing around 38g of carbohydrates per bar to help fuel training, support recovery and make consistent fuelling easier.
References
International Olympic Committee (IOC) RED-S Consensus Statements (2014, 2018, 2023).
Holtzman B, Kelly RK, Saville GH, et al. Low energy availability surrogates are associated with Relative Energy Deficiency in Sport outcomes in male athletes. British Journal of Sports Medicine. 2024.
Marzuki MIH, Jamil NA, Mohamad MI, et al. Energy availability and its association with health-related outcomes among national athletes at risk of RED-S. BMJ Open Sport & Exercise Medicine. 2024.
