Original episode & show notes | Raw transcript
This document provides a detailed exploration of the key concepts surrounding athlete health as discussed in the podcast featuring Dr. Traci Carson, an epidemiologist specializing in female athlete health. We will unpack the evolution of scientific understanding, the underlying physiology, and the practical implications for athletes, coaches, and clinicians.
The conversation around the health consequences of underfueling in athletes began with a narrower focus, which has since expanded to be more inclusive and comprehensive.
The Female Athlete Triad: First formally defined in the early 1990s, the “Female Athlete Triad” identified a cluster of three interrelated conditions seen in female athletes:
Low Energy Intake: This was often, but not always, linked to disordered eating or clinical eating disorders.
Menstrual Dysfunction: Ranging from irregular cycles (oligomenorrhea) to the complete absence of a period (amenorrhea).
Low Bone Mineral Density: Leading to an increased risk of stress fractures and long-term conditions like osteoporosis.
The Shift to RED-S: Researchers and clinicians began to recognize that the consequences of underfueling were not limited to women or to just these three outcomes. This led the International Olympic Committee (IOC) to introduce a broader framework in 2014: Relative Energy Deficiency in Sport (RED-S).
RED-S acknowledges that the root cause—low energy availability—affects a wide array of bodily functions and performance metrics in both male and female athletes. The Female Athlete Triad is now considered to exist within this more comprehensive RED-S model.
LEA is the foundational cause of RED-S. It is a state where the body does not have enough energy to support all of its physiological functions after the energy cost of exercise has been subtracted.
The Scientific Definition: Energy Availability (EA) is calculated with the following formula:
EA = (Energy Intake [kcal] - Exercise Energy Expenditure [kcal]) / Fat-Free Mass [kg]
Key Thresholds: Research, conducted primarily on female athletes, has established critical thresholds:
Optimal Function: An EA of ~45 kcal/kg of fat-free mass (FFM) per day is generally considered optimal for supporting normal physiological function and health.
Impaired Function: An EA below 30 kcal/kg FFM/day is strongly associated with significant health consequences, such as menstrual dysfunction and stress fractures.
The “At-Risk” Zone: The range between 30-45 kcal/kg FFM/day is a gray area where athletes may begin to experience negative effects.
Challenges in Calculation: As noted in the podcast, accurately calculating one’s own EA is difficult. Wearable technology provides rough estimates of energy expenditure at best, and factors like resting metabolic rate and non-exercise activity vary significantly between individuals.
Intentional vs. Unintentional LEA: It is critical to understand that LEA is not synonymous with an eating disorder.
Unintentional LEA: An athlete may simply be uneducated about their high energy needs and not consume enough food to match their training load.
Intentional LEA: This involves conscious restriction of food intake, which exists on a spectrum from disordered eating patterns to clinically diagnosed eating disorders.
If LEA is the cause, RED-S is the resulting syndrome. The RED-S framework illustrates how energy deficiency impacts ten key areas of health and performance.
Physiological Consequences:
Endocrine: Disruption of hormones, including reproductive and thyroid hormones.
Menstrual Function: Irregular or absent cycles in females.
Bone Health: Reduced bone formation, leading to stress fractures and osteoporosis.
Metabolic: Lowered resting metabolic rate as the body tries to conserve energy.
Hematological: Potential for issues like iron deficiency anemia.
Immunity: Increased susceptibility to illness and infection.
Cardiovascular: In chronic cases, issues like low heart rate (bradycardia) and low blood pressure can arise.
Gastrointestinal: Problems with digestion and nutrient absorption.
Growth & Development: Impaired development in adolescent athletes.
Psychological: Can be both a cause and a consequence, with links to anxiety, depression, and irritability.
Performance Consequences:
Decreased endurance, muscle strength, and coordination.
Impaired glycogen stores.
Poor response to training and prolonged recovery times.
Increased injury risk.
Decreased concentration and judgment.
Dr. Carson highlighted several crucial points that challenge common assumptions about athlete health and body weight.
You Cannot Judge Health by Appearance: An athlete can be in a chronic state of LEA and suffering from RED-S without being underweight. They can maintain a stable body weight or even gain weight as their metabolism slows down to adapt to the energy deficit. A “lean” or “athletic” appearance is not a reliable indicator of adequate fueling.
Metabolic Adaptation: The body is incredibly adaptive. In a state of chronic LEA, it will slow down non-essential functions to conserve energy. This “metabolic adaptation” is why many athletes who restrict calories eventually hit a plateau in weight loss and feel fatigued—their body is actively fighting to conserve resources.
Signs in Male Athletes: While men do not have a menstrual cycle to serve as a clear biomarker, they are not immune to RED-S. The primary signs in men include low libido and the loss of spontaneous morning erections, which are indicators of suppressed testosterone and endocrine dysfunction.
The Masking Effect of Hormonal Contraception: For female athletes, hormonal birth control can create a chemically induced “withdrawal bleed” that mimics a period. This can mask the underlying sign of amenorrhea, preventing the athlete and their support team from recognizing that they are in a state of LEA.
The Importance of Nutrient Timing: Even if an athlete’s total caloric intake for a 24-hour period is sufficient, large within-day energy deficits can still trigger a stress response and lead to RED-S symptoms. For example, training for several hours in a fasted state creates a significant energy deficit that the body must manage, even if calories are replaced later in the day. Consistent fueling around training is essential.
Bone Health is Paramount: The most significant long-term consequence is compromised bone health. Peak bone mass is built during adolescence and young adulthood. Damage done during this critical window is largely irreversible. An athlete who suffers from RED-S in their teens or twenties may face a lifetime of recurring stress fractures and an early onset of osteoporosis.
Prevention and Intervention:
Education: The primary preventative tool is education for athletes, parents, and coaches about energy needs and the risks of underfueling.
Prioritizing Fueling and Recovery: Nutrition and sleep should be treated as integral parts of training, not as optional extras.
Professional Guidance: For athletes struggling, a multi-disciplinary team is often necessary, including a sports-focused registered dietitian and, if disordered eating is present, a therapist or psychologist.
Shifting Cultural Norms: Challenging the “leaner is better” mentality within sports culture is crucial. As highlighted in the podcast, focusing on being the “best-fueled athlete on the start line” is a powerful and healthy mindset.