The assertion that Relative Energy Deficiency in Sport (RED-S) doesn’t exist might sound provocative, but it forms the core of a new 2024 scientific paper. If this makes you wonder, “Of course it exists, what is this paper talking about?”, let’s explore the authors’ arguments.
The central premise of the article, led by the renowned exercise physiologist and nutritionist Asker Jeukendrup, is this: are we overly focused solely on energy balance, and are there other factors explaining the conditions athletes attribute to RED-S? It’s likely that this is indeed the case.
What Does RED-S Share with Other Conditions?
Initially, RED-S was known as the “Female Athlete Triad”—a condition specific to women involving disordered eating, amenorrhea, and low bone mineral density. In 2014, the International Olympic Committee (IOC) broadened this concept to RED-S, making it non-gender-specific and incorporating numerous other signs and symptoms observed in athletes.
Simply put, RED-S is characterized by insufficient energy availability—meaning there’s not enough energy left over to support normal physiological functions after accounting for exercise demands. The latest updates to its definition occurred in 2023.
Many of RED-S’s signs and symptoms are extensive and can affect various bodily systems:
- Reduced metabolic activity
- Poor bone health
- Cessation of menstruation
- Blood test abnormalities (e.g., low iron, B12, folate)
- Reduced libido and erectile dysfunction
- Impaired concentration and athletic performance
- Chronic fatigue
- Sleep disturbances
- Digestive issues (constipation)
In this new work, the authors suggest that RED-S symptoms are likely a result of not just energy deficit, but also many other contributing factors. This viewpoint is supported by the significant overlap in symptoms between RED-S and Overtraining Syndrome.
Stress, the HPA Axis, and Systemic Effects
Any stress on the body—whether from intense training, competitions, lack of sleep, travel, or life difficulties—impacts the hypothalamic-pituitary-adrenal (HPA) axis in the brain. This system is crucial for managing stress.
Since many bodily functions are automatically regulated by the nervous system, disruptions in the HPA axis can trigger a wide range of effects across different systems. This explains why symptoms in overtraining or low-energy states can be so diverse and “scattered.”
A Shift in Approach: General Adaptation Syndrome and Allostatic Load
The authors emphasize that they are not seeking to replace or completely revise the RED-S concept. Instead, they propose using broader models: the General Adaptation Syndrome (GAS) and the Allostatic Load model.
General Adaptation Syndrome (GAS)
The GAS model describes the body’s response to stress in three stages:
- Alarm: Detection of a stressor (intense training, life stress, illness) and activation of a short-term response.
- Resistance: Adaptation and coping with stress. With sufficient recovery, positive changes occur at this stage (e.g., improved physical fitness).
- Exhaustion: If stress continues without adequate recovery, the body’s resources become depleted, leading to fatigue, illness, injuries, or decreased performance.
It’s important to remember that the perception of stress also influences coping strategies. Healthy recovery strategies differ from restrictions, overtraining, or avoidance, and all depend on how we interpret stress. Stress is not only physical but also psychological.
The Allostatic Load Model
The Allostatic Load model builds upon GAS. “Allostasis” means maintaining stability through change. When the body encounters new or increasing stress, hormones, the nervous system, immune function, and metabolism adapt to help cope (e.g., increased hemoglobin mass during altitude training).
However:
- One stressor increases the load.
- Multiple stressors accumulate.
- Over time, cumulative stress becomes an allostatic load.
If this load remains high for too long, it causes “wear and tear” on the cardiovascular, hormonal, immune, metabolic, and reproductive systems.
A clear example of cumulative stress: an athlete maintains the same training load while life stress increases—work deadlines, family responsibilities, or financial pressure. As many coaches say, stress is stress. Perhaps this is worth considering when examining RED-S.
Can there be an energy deficit? Absolutely.
Can this be the primary stressor causing symptoms? Certainly.
But couldn’t it also be that you’re slightly under-fueling, getting insufficient sleep, and experiencing additional life stress this season? Often, though not always, this is the case. It’s a combination of issues that ultimately leads to an athlete’s health and performance decline.
The “Stress Bucket” Analogy
A helpful visualization combining overtraining, RED-S, allostasis, and GAS is the “stress bucket” analogy.
Each of us has a finite capacity for stress—our bucket. As stressors are added (training load, sleep deprivation, children, poor nutrition, illness, travel), the bucket fills up. Without adequate recovery, the bucket overflows.
In the context of athletes, this model explains why performance decline or RED-S-related symptoms rarely have a single cause. Instead, they often result from accumulated stress across multiple domains.
The authors identify eight domains that can contribute to symptoms in struggling athletes:
- Training Stress: Load, intensity, volume, monotony.
- Life Stress: Work, family, competitions, travel, social pressure.
- Mental Health: Depression, anxiety, major life events.
- Disordered Eating: Restrictions or unhealthy eating habits.
- Nutrition: Low energy value, insufficient carbohydrate/protein intake, micronutrient deficiencies.
- Sleep: Poor quality or insufficient quantity of sleep.
- Infections: Anything from frequent colds to lingering illnesses.
- Medical Conditions: Thyroid, metabolic, cardiac, or other pathologies.
The Bigger Picture
When things start to unravel—or when we try to understand the reasons for stagnation in health or performance—it is crucial to consider the complete picture. Assessing these eight domains can be an excellent starting point. Such self-assessment is difficult to conduct alone and objectively. This is precisely why having a team—dietitians, doctors, mentors, coaches, friends—matters.
In professional and collegiate sports, support teams monitor training load, discuss life challenges, and jointly adjust plans to help athletes perform at their best in sport and life. For amateur athletes, or those training independently who often lack such an integrated team, the question arises: can we raise awareness and help them build their own support system?
Because perhaps the question isn’t, “Does RED-S exist?” but rather, “When stress accumulates, what’s the best way to adapt—and who is in your corner to help you protect your health, longevity in sport, and performance?”