Comprehensive Clinical Guide to Relative Energy Deficiency in Sport (REDS)

Conceptual Foundations and Evolution of REDS

• Historical Evolution of Terminology:

  • In $1992$, the American College of Sports Medicine (ACSM) originally conceptualized this clinical condition as the Female Athlete Triad, characterized by three interrelated components:
  • Low energy availability (with or without disordered eating)
  • Menstrual dysfunction (such as amenorrhea)
  • Low bone mineral density (osteopenia or osteoporosis)
  • In $2014$, the International Olympic Committee (IOC) introduced the term Relative Energy Deficiency in Sport (RED-S or REDS) after clinical evidence demonstrated that male athletes also experience the debilitating physiological and psychological sequelae of low energy availability.
  • In $2018$, the IOC published an updated consensus statement refining the understanding of systemic impairments across organ systems.
  • In $2023$, the IOC released its most comprehensive consensus statement to date, formalizing advanced clinical models, refined risk stratification tools (REDS CAT II), and novel distinctions between adaptable and problematic low energy availability.

• Formal Clinical Definition ($2023$ Consensus Statement):

  • Relative Energy Deficiency in Sport (REDS) is defined as a syndrome of impaired physiological and/or psychological functioning experienced by female and male athletes that is caused by exposure to problematic, prolonged, and/or severe low energy availability (LEA).
  • Systemic physiological consequences involve, but are not limited to, decrements in:
  • Energy metabolism and metabolic rate
  • Reproductive function and sex hormone production
  • Musculoskeletal health and bone remodeling
  • Immunological function and infection resistance
  • Glycogen synthesis and cellular energy replenishment
  • Cardiovascular health and autonomic stability
  • Endocrine regulation and growth pathways
  • Primary sport-specific and functional manifestations include:
  • Substantially impaired psychological well-being and cognitive performance
  • Elevated incidence and recurrence of musculoskeletal and bone stress injuries
  • Marked reductions in training response and athletic performance

• Clinical Delivery and Interdisciplinary Paradigms:

  • Contemporary REDS management is grounded in empirical science rather than clinical guesswork, utilizing individualized protocols tailored to the athlete's specific physiological profile and sporting demands.
  • Management requires synchronized interdisciplinary collaboration among:
  • Sports Registered Dietitians (Sports RD / Nutritionists)
  • Athletic Trainers (ATs)
  • Physical Therapists (PTs)
  • Sports Medicine Physicians
  • Sports Psychologists
  • Strength and Conditioning / Performance Coaches
  • Athletic trainers occupy a vital front-line surveillance role because their day-to-day contact hours with athletes routinely exceed those of specialty staff overseeing wide cohorts (such as an Olympic sports director overseeing Men's and Women's basketball, volleyball, track and field, lacrosse, and soccer).

Energy Availability: Energetics, Calculations, and Systemic Homeostasis

• Mathematical Modeling of Energy Availability (EA):

  • Energy Availability represents the quantity of dietary energy remaining for foundational physiological processes once the energetic cost of exercise has been subtracted.
  • The standardized clinical equation is:     $\text{Energy Availability (EA)} = \frac{\text{Energy Intake (EI)} - \text{Exercise Energy Expenditure (EEE)}}{\text{Fat-Free Mass (FFM)}}$
  • Units are expressed in kilocalories per kilogram of fat-free mass per day ($\text{kcal/kg FFM/day}$).

• Quantitative Energy Availability Thresholds:

  • Optimal Energy Availability: $\ge 45\,\text{kcal/kg FFM/day}$
  • Provides sufficient energetic capital to sustain baseline metabolic homeostasis, robust reproductive function, skeletal remodeling, immune vigilance, tissue repair, and athletic training adaptations.
  • Subclinical / Low Energy Availability: Between $30\,\text{kcal/kg FFM/day}$ and $45\,\text{kcal/kg FFM/day}$
  • Represents a transitional state where subtle subclinical hormonal alterations or mild impairments can begin to manifest.
  • Severe / Problematic Low Energy Availability: $< 30\,\text{kcal/kg FFM/day}$
  • Clinical threshold below which severe multisystem physiological impairments, hormonal downregulation, musculoskeletal failure, and symptomatic REDS emerge.

• Homeostatic Prioritization and Energy Partitioning:

  • Biological homeostasis represents the body's optimal physiological steady-state, requiring continuous caloric allocation across two major domains:
  • Baseline Non-Exercise Physiological Needs: Cellular maintenance, tissue growth and protein synthesis, organ function, thermoregulation, immune surveillance, neurotransmitter synthesis and mood regulation, reproductive endocrine cycles, and bone remodeling.
  • Athletic Demands: Daily physical training, competition movement, muscular adaptation, and post-exercise recovery.
  • When caloric intake is insufficient to cover both biological and athletic demands, the body initiates an adaptive survival hierarchy:
  • Top Priority: Essential survival mechanisms (vital organ function and basal cellular integrity) and external exercise demands (athletes persistently execute training sessions despite severe energetic deficits).
  • Deprioritized Systems: The body places non-survival systems onto the "back burner," systematically downregulating immunity, bone remodeling, reproductive cycles, and cognitive-emotional health.

• Conceptual Classifications from the $2023$ Consensus Statement:

  • Adaptable Low Energy Availability:
  • Acute, short-duration under-fueling episodes (e.g., $1 - 2\,\text{days}$ of transient caloric deficit due to acute scheduling conflicts or travel).
  • Systemic changes remain fully reversible with minimal structural or physiological disruption upon rapid energetic restoration.
  • Problematic Low Energy Availability:
  • Prolonged, severe, or repeated exposure to energy deficits.
  • Generates deep disruptions across neuroendocrine, metabolic, and musculoskeletal systems, requiring prolonged clinical, nutritional, and psychological rehabilitation to reverse.

Signs, Symptoms, and Multi-System Clinical Manifestations

• Top-Down Neurological and Cognitive Manifestations:

  • Persistent psychological fatigue, blunted alertness, and difficulty concentrating.
  • Heightened emotional lability, irritability, and depressive symptoms.
  • Dizziness, lightheadedness, and orthostatic instability.
  • Pathological blunting of appetite regulation caused by disruptions to circulating hunger hormones (e.g., ghrelin and leptin).

• Behavioral and Dietary Signs:

  • Preoccupation with food, ritualistic eating routines, and obsessive dietary tracking.
  • Unwarranted elimination of specific foods, food macronutrients, or entire food groups.
  • Disordered eating habits or social avoidance during team meal functions.

• Reproductive and Endocrine Alterations:

  • Female athletes: Functional hypothalamic amenorrhea (absence of menses) or oligomenorrhea (cycles spaced $> 35\,\text{days}$ apart).
  • Male athletes: Suppressed free and total circulating testosterone, diminished libido, and reduced erectile function.

• Musculoskeletal and Injury Sequelae:

  • Impaired osteoblast activity and uncoupled bone remodeling leading to diminished bone mineral density (BMD).
  • Repeated bone stress injuries (BSI), stress reactions, and frank stress fractures.
  • Prolonged, non-responsive rehabilitation timelines for soft tissue and orthopedic injuries.
  • Unexplained loss of muscular strength, power output, and training stagnation.
  • Progressive muscle wasting (loss of fat-free mass) and prominent skeletal landmarks.

• Gastrointestinal (GI) and Immune Dysfunction:

  • Hypomotility, abdominal bloating, cramping, and severe persistent constipation.
  • Heightened susceptibility to recurrent upper respiratory tract infections, systemic illnesses, and delayed wound healing.

• Cardiovascular and Thermoregulatory Derangements:

  • Resting sinus bradycardia (abnormally low heart rate).
  • Hypotension (abnormally low blood pressure) and symptomatic postural orthostatic shifts within $10\,\text{seconds}$ of rising from supine to standing.
  • Core body hypothermia, cold intolerance, and acrocyanosis.

Distinguishing REDS from Eating Disorders

• Clinical Separation and Coexistence:

  • REDS and eating disorders (ED) are distinct clinical entities that frequently overlap, but they are not synonymous.
  • An athlete diagnosed with an eating disorder frequently exhibits REDS due to severe, purposeful caloric restriction.
  • Not all athletes with REDS meet diagnostic criteria for an eating disorder; many suffer from unintentional low energy availability driven by high training volumes, scheduling challenges, or nutritional illiteracy.

• Diagnostic Comparison:

  • Eating Disorder (ED):
  • A formal psychiatric and mental health disorder defined by persistent disturbances in eating behaviors accompanied by severe cognitive distress, body image distortion, and obsessive thoughts regarding food, weight, and shape.
  • Relative Energy Deficiency in Sport (REDS):
  • A systemic physiological syndrome induced by an imbalance between energy intake and exercise expenditure, which may occur completely independent of psychopathology.

• Divergence in Treatment Frameworks:

  • REDS Treatment Protocol:
  • Centers on energetic restoration, targeted increases in caloric and macronutrient intake, deliberate adjustments to exercise volume and training load, and corrective education for any secondary disordered eating habits.
  • Eating Disorder Treatment Protocol:
  • Demands specialized higher-level psychiatric and psychological interventions, intensive cognitive behavioral therapy, medical stabilization, and multi-tiered clinical management alongside dietary restructuring.

Etiology, Prevalence, and Risk Factors

• Primary Etiological Categories:

  • High Energy Expenditure Drivers:
  • High physical training demands and prolonged practice sessions.
  • Pathological exercise dependence and surreptitious workouts completed outside prescribed team sessions.
  • Massive absolute caloric requirements (e.g., collegiate men's basketball players standing over $7\,\text{ft}$ tall expending upwards of $7,000\,\text{kcal/day}$).
  • Inadequate Energy Intake Drivers:
  • Nutritional literacy deficits: Athletes unaware of baseline energetic requirements to sustain performance.
  • Structural and logistical challenges: Mid-day class and training blocks preventing midday meals (e.g., eating breakfast, completing a $3\,\text{hour}$ practice session, and delaying lunch).
  • Food accessibility and functional barriers: Freshman transitions to collegiate dining halls, unpalatable cafeteria options, or limited ability to grocery shop and cook independently (especially while navigating physical disability or orthopedic injury).
  • Exercise-induced appetite suppression: Blunted hunger signaling resulting from heavy training in high ambient heat.
  • Strict dietary patterns: Inappropriately managed vegan, vegetarian, or allergy-restricted diets (such as lactose intolerance altering team catering).
  • Socio-cultural and psychological pressures: Team cultures valorizing thinness, body dysmorphia, perfectionism, social media pressures, and overt pressure from coaching staffs.

• Sport-Specific Prevalence and Environmental Risks:

  • Data from the Gatorade Sports Science Institute (GSSI) highlights high LEA prevalence across diverse sports:
  • Weight-class sports: Rowing (lightweight categories), wrestling, Olympic weightlifting.
  • Aesthetic sports: Gymnastics, synchronized swimming, figure skating, diving (where athletes experience severe pressure regarding uniforms, leotards, or weigh-ins, sometimes resorting to periodic multi-day fasting).
  • Gravitational and endurance sports: Distance running, track and field, cycling, triathlon.
  • Team sports: Lacrosse, soccer, softball.
  • Total Daily Energy Expenditure Context:
  • The duration of active sport participation does not solely dictate energetic output.
  • Sports requiring long durations of field standing (e.g., baseball over $6\,\text{hours}$) or collegiate athletes walking extensive distances across large university campuses accumulate massive background caloric expenditures that exacerbate energy deficits if left unreplenished.

• Coaching Influence and Institutional Dynamics:

  • Misguided coaching mandates frequently precipitate athlete under-fueling (e.g., coaches banning cream-based sauces at team dinners out of unfounded fears of dietary fat, despite student-athletes expending $3,000+\,\text{kcal/day}$).
  • Inadequate travel nutrition provided by athletic programs (e.g., relying solely on pizza after a high-intensity $90\,\text{minute}$, $7\,\text{mile}$ soccer competition) fails to provide the necessary macronutrients for glycogen resynthesis and cellular repair.
  • Destructive coaching comments targeting an athlete's physical appearance, uniform fit, or arbitrary "competition weight" directly trigger body image pathology and caloric restriction.
  • Professional advocacy requires sports dietitians and athletic trainers to confront coaches directly or escalate harmful coaching practices to sport administrators to safeguard athlete welfare.

Multidisciplinary Assessment, Objective Screening, and the REDS CAT II Model

• Comprehensive Screening Tools and Multimodal Assessment:

  • There is no single standalone clinical test that confirms REDS; diagnosis requires an exhaustive evaluation across clinical domains within the Nutrition Care Process (NCP):
  • Anthropometrics and Body Composition Tracking: Longitudinal monitoring of weight fluctuations and lean tissue changes. Tools include dual-energy X-ray absorptiometry (DEXA), air displacement plethysmography (Bod Pod), and multi-frequency bioelectrical impedance (e.g., InBody devices used to calculate fat-free mass for the energy availability formula).
  • DEXA Bone Mineral Density Testing: Standardized imaging yielding $Z$-scores and $T$-scores to detect osteopenia or osteoporosis, ordered by sports medicine physicians in severe cases or following bone stress fractures.
  • Omission of Body Mass Index (BMI): BMI is clinically invalid and contraindicated for assessing athletic populations because it fails to differentiate between skeletal muscle mass and adipose tissue, often erroneously classifying highly muscular athletes as clinically obese.
  • Food and Nutrition History: Diet recalls, nutritional literacy evaluations, appetite scoring, food access assessments, and documentation of attitudes, beliefs, or familial influences surrounding food.
  • Clinical Health History: Menstrual history, musculoskeletal injury records, bone stress injury recurrence, history of clinical depression or anxiety, sleep disruption (onset or maintenance insomnia), and detailed gastrointestinal history (stool consistency, frequency, bloating, and constipation).
  • Nutrition-Focused Physical Exam: Evaluation for temporal and clavicular muscle wasting, loss of orbital fat, prominent bony architecture, core temperature hypothermia, orthostatic vital sign testing, and cardiac auscultation.

• Laboratory Biomarkers and Biochemical Testing:

  • Endocrine and Metabolic Markers:
  • Suppressed circulating leptin (regulator of energy balance and satiety; note that lab turnaround times can extend to $2\,\text{weeks}$, reflecting a retrospective indicator).
  • Decreased thyroid panel: Free triiodothyronine ($T_3$), thyroxine ($T_4$), and thyroid-stimulating hormone (TSH).
  • Suppressed reproductive steroids: Estradiol and progesterone in non-contraceptive females; subnormal free and total testosterone in males.
  • Suppressed fasting insulin and fasting serum glucose.
  • Suppressed Insulin-like Growth Factor 1 (IGF-1).
  • Elevated resting morning serum cortisol.
  • Hematological and Lipid Profiles:
  • Decreased serum ferritin, iron saturation, and total iron levels (iron deficiency anemia).
  • Elevated serum total cholesterol and low-density lipoprotein (LDL) cholesterol (paradoxical hypercholesterolemia triggered by severe metabolic starvation).

• Structural Workflow of the IOC REDS CAT II ($2023$ Consensus Model):

  • Step 1: Pre-participation Screening:
  • Administered via validated questionnaires and comprehensive clinical interviews during pre-participation physical exams. If an athlete flags positive or exhibits elevated risk, they proceed to Step 2.
  • Step 2: Severity Risk Stratification:
  • Categorizes athletes into risk tiers (Green = Low Risk; Yellow = Mild Risk; Orange = Moderate Risk; Red = High/Severe Risk) determined by the clinical tally of specific indicators:
  • Severe Primary Indicators: Functional hypothalamic amenorrhea, severe hypogonadism in males, critically suppressed bone mineral density ($Z$-score $< -2.0$ accompanied by bone stress injuries).
  • Primary Indicators: Secondary amenorrhea, subclinical testosterone suppression, low thyroid hormone levels, recurrent bone stress injuries, or low BMD ($Z$-score $< -1.0$).
  • Secondary Indicators: Oligomenorrhea (menstrual cycle length $> 35\,\text{days}$), single low-risk bone stress injury in the prior $2\,\text{years}$, elevated total or LDL cholesterol, clinically diagnosed anxiety or depression.
  • Other Potential Indicators: Blunted resting metabolic rate ($\text{RMR} < 30\,\text{kcal/kg FFM/day}$), suppressed IGF-1, elevated resting cortisol, urinary incontinence, sleep architecture fragmentation, acute drops in ferritin, resting bradycardia, resting hypotension, and exercise dependence.
  • Step 3: Diagnostic Integration and Treatment Action Plan:
  • Sports medicine physician makes the formal medical diagnosis.
  • Implementation of a multidisciplinary care protocol that outlines training parameters or, when medical safety criteria are breached, mandates partial or full removal from sport via an athlete behavioral contract.

Clinical Case Study: Collegiate Track/Field or Olympic Sport Athlete ("Jane")

• Initial Profile and Baseline Presentation:

  • Demographics: Female freshman collegiate student-athlete residing in a campus dormitory.
  • Initial Consultation: Self-referred to sports nutrition to proactively optimize athletic performance.
  • Baseline Nutritional Assessment: Highly compliant, meeting $100\%$ of calculated daily caloric needs via balanced meals. Expressed minor transitional stress regarding meal preparation in the dorms and an initial reliance on grab-and-go convenience items.
  • Initial Interventions: Education on macronutrient balancing, plate composition, and increasing lean protein intake.

• Clinical Crisis and Symptom Emergence:

  • Timeline: One month following initial intake, the athlete presented with an acute tibial stress fracture and high subjective distress.
  • Coaching Pressure: The head coach contacted the sports dietitian expressing concern that the athlete had gained $10\,\text{lb}$ across a $4\,\text{month}$ span, demanding an immediate body composition assessment.
  • Multi-tiered Diagnostic Response:
  • Implementation of the institutional Injury Nutrition Protocol.
  • InBody body composition testing to quantify fat-free mass and evaluate energy availability.
  • Experiential nutrition education via an interactive grocery store tour at Trader Joe's to establish balanced, dorm-friendly cooking strategies.
  • Laboratory blood draw referral to sports medicine and a referral to sports psychology to address severe distress.

• Laboratory and Energetic Findings:

  • Biochemical Panel: Markedly suppressed serum leptin and deficient circulating vitamin D.
  • Clinical Symptomatology: Persistent fatigue, generalized lethargy, and low energy despite normal sleep durations.
  • Energetic Calculations:
  • Daily caloric intake: Approximately $1,900\,\text{kcal/day}$, representing severe under-fueling for an elite collegiate athlete with high healing demands.
  • Initial Calculated Energy Availability: $16\,\text{kcal/kg FFM/day}$, falling dramatically below the severe LEA cutoff of $30\,\text{kcal/kg FFM/day}$.

• Subsequent Deterioration and Root-Cause Unveiling:

  • Behavioral Changes: The athlete began preparing meals independently in the dorms, restricted fast foods, but progressively developed meal-skipping patterns.
  • Objective Energetic Decline:
  • Daily intake plummeted to only $65\%$ of daily requirements.
  • Energy availability deteriorated further to $14\,\text{kcal/kg FFM/day}$.
  • Psychosocial Etiology: The athlete revealed that months prior, her coach criticized her body, stating her shirts appeared "more snug" and demanding that she return to her former "competition weight." This catalyzed body dysmorphia, restrictive eating, and severe emotional distress.

• Interdisciplinary Intervention and Clinical Recovery:

  • Nutritional Therapy: Weekly sessions with the sports RD; deployment of the mobile tracking app Nourishly for meal photography, hunger-satiety logging, and emotional tracking around eating without numerical calorie obsession.
  • Psychology: Weekly cognitive therapy sessions with the sports psychologist to deconstruct body dysmorphia and restrictive mindsets.
  • Sports Medicine: Monthly physician visits with serial biomarker testing; structured vitamin D supplementation protocols.
  • Athletic Training and Physical Therapy: Guided rehabilitation for the tibial stress fracture, incorporating modified conditioning and aquatic training.
  • Clinical Outcome: Resolution of the tibial stress fracture, progressive normalization of energy availability, restoration of healthy dietary patterns, and a successful return to competition.

Management, Treatment Frameworks, and Rehabilitation Protocols

• Nutritional Rehabilitation Principles for Injury and REDS:

  • Caloric Modification in Injury Management:
  • The assumption that athletes must decrease caloric intake during injury rehabilitation due to physical inactivity is clinically false.
  • Orthopedic trauma, surgical intervention, and physiological tissue remodeling substantially elevate basal metabolic expenditure.
  • Caloric intake must be sustained or strategically increased, prioritizing foundational recovery building blocks (adequate carbohydrates for glycogen replenishment, high-quality complete proteins for collagen and muscle synthesis, and micronutrient support like vitamin D and calcium) rather than nutrient-void foods.
  • Preemptive Surveillance and Objective Biometrics:
  • Utilization of continuous force plate testing during strength training sessions to assess athlete "system weight."
  • Integration of Athlete Management Systems (AMS) with automatic threshold alerts to flag acute or progressive weight drifts (positive or negative) for clinical check-ins.
  • Routine nutritional presence to destigmatize seeking care, preventing the dietitian from being perceived as a disciplinary figure.

• Physical Activity Modification Paradigms:

  • Complete cessation of all athletic activity should be avoided whenever medically safe.
  • Abruptly stripping away all sport participation damages athletic identity, provokes feelings of alienation and punishment, and exacerbates underlying psychological distress.
  • Clinical practice utilizes modified mechanical loading: Non-impact cross-training, pool running, aquatic conditioning, and targeted upper-extremity training to sustain fitness, mental health, and social connection while healing bone and soft tissue injuries.

• Formal Behavioral and Medical Safety Contracts:

  • In severe, non-responsive, or high-risk REDS scenarios (particularly with comorbid eating disorders), an interdisciplinary contract signed by the physician, athletic trainer, sports psychologist, dietitian, and athlete is established.
  • The contract outlines mandatory compliance benchmarks (caloric adherence, laboratory parameters, weight stability, therapy attendance).
  • Failure to meet required criteria results in immediate medical disqualification from training and competition to protect the athlete's long-term health.

Questions & Discussion

• Question on Caloric Manipulation During Injury Rehabilitation:

  • Prompt: During periods of injury, orthopedic trauma, or post-surgical recovery, should an athlete restrict their caloric intake or increase their caloric intake?
  • Response:
  • Caloric intake must be maintained or increased. Metabolic demand rises substantially post-injury to fuel cellular repair, tissue regeneration, and structural remodeling.
  • Restricting calories prolongs the recovery process, impairs collagen and protein synthesis, and exacerbates energetic deficits.
  • Nutritional strategies must emphasize high-quality building blocks—targeted protein distribution, complex carbohydrates, and micronutrients—rather than indiscriminate food choices.

• Question on Aesthetic Sports and Adaptive vs. Problematic Low Energy Availability:

  • Prompt: In sports with intense aesthetic pressures like women's gymnastics, where athletes fast before weigh-ins or to fit into leotards, does this represent adaptable or problematic low energy availability?
  • Response:
  • Both phases occur within aesthetic sports.
  • A brief fast lasting a day or two around a weigh-in may initially manifest as adaptable low energy availability if short-lived and rapidly reversed.
  • However, because these behaviors recur chronically throughout a competitive season, the cumulative physiological insult transitions into problematic low energy availability, resulting in persistent neuroendocrine suppression, bone loss, and heightened injury risk.

• Question on Chronicity and Recurrence of REDS:

  • Prompt: Once an athlete is diagnosed with and treated for low energy availability, how common is it for them to experience recurrent problems, or is recovery typically a permanent fix once they are educated?
  • Response:
  • Recovery from REDS is rarely an acute, open-and-shut fix; it frequently trails off into a long, non-linear continuum.
  • While some athletes rapidly correct their intake once provided with education and meal-planning resources, many remain vulnerable to relapse.
  • Environmental stressors—such as competitive season pressure, travel fatigue, academic demands, coaching changes, or roster transitions—can trigger recurrent under-fueling and physiological regression.
  • Long-term surveillance, ongoing interdisciplinary support, and preemptive screening are essential across an athlete's collegiate tenure and subsequent career.

• Discussion on Atypical Bone Stress Presentations as Diagnostic Catalysts:

  • Prompt: Discussion regarding how unconventional injury sites trigger deeper nutritional and psychological assessments.
  • Response:
  • An example discussed was a jumping athlete presenting with a femoral shaft stress reaction, an atypical and rare site for that sporting profile (compared to common lower-extremity sites such as the navicular or tibia).
  • This atypical presentation catalyzed a comprehensive investigation into food hygiene, energetic balance, and psychological health.
  • The evaluation revealed that while the athlete verbally claimed to be "fine," they were experiencing severe unexpressed internal distress ("FINE: Feelings Inside Not Expressed"), inadequate fueling, and disrupted sleep, which directly contributed to structural skeletal failure.