One of the most common misconceptions in sports nutrition is that if an athlete’s weight hasn’t changed, they must be eating enough. At first glance, it seems logical. If you’re training hard, have weight stability, and are not experiencing dramatic changes on the scale, then surely your nutrition is meeting your needs, right? Not necessarily.
In fact, some of the athletes I see struggling the most with Relative Energy Deficiency in Sport (REDs) haven’t lost weight at all. Their weight is stable. Their BMI falls within the “normal” range. They may even be told they’re healthy because they don’t fit the stereotypical image of an underfueled athlete.
Yet beneath the surface, their bodies are showing clear signs of physiological dysfunction.
The truth is that weight stability does not equal adequate fueling.
The Body Is Designed to Adapt
One of the most remarkable things about the human body is its ability to adapt.
When energy intake consistently falls short of the body’s needs, the body doesn’t simply wave a white flag and stop functioning.
Instead, it gets resourceful.
The body begins conserving energy wherever possible to prioritize survival.
This is one of the hallmarks of REDs.
Rather than continuing to operate at full capacity, the body starts making trade-offs:
- Metabolism slows
- Hormone production decreases
- Recovery becomes less efficient
- Bone turnover is altered
- Immune function declines
- Performance begins to suffer
Unfortunately, these adaptations can occur long before noticeable weight loss appears.
Suppressed Resting Metabolic Rate: The Hidden Adaptation
One of the most important physiological adaptations seen in REDs is suppression of resting metabolic rate (RMR).
Resting metabolic rate represents the energy your body uses simply to keep you alive, supporting essential functions such as breathing, circulation, temperature regulation, hormone production, and cellular repair.
When energy availability remains low for an extended period of time, the body may reduce energy expenditure in an attempt to conserve fuel.
In clinical practice, researchers often assess this using the ratio of measured RMR to predicted RMR. A ratio below 0.90 is considered a potential marker of metabolic suppression and may indicate chronic low energy availability.
In practical terms, this means the body is intentionally burning fewer calories than expected.
This adaptation may help preserve body weight in the short term, but it comes at a cost.
Athletes may find themselves experiencing:
- Persistent fatigue
- Feeling cold frequently
- Poor workout recovery
- Decreased training adaptations
- Sleep disturbances
- Brain fog
- Reduced motivation
Yet because their weight remains stable, the underlying problem is often missed.
Why Weight Can Stay Stable Despite Underfueling
Many athletes assume that underfueling automatically leads to weight loss. However, the body is not a simple calorie calculator.
As metabolic adaptations occur, weight loss may slow dramatically or stop altogether. Some athletes even experience weight gain while chronically underfueling.
This can feel incredibly frustrating.
They may be eating less, training more, and seeing little change on the scale. In response, they often restrict food further, unknowingly deepening the cycle of low energy availability.
This is physiology at play and the body doing exactly what it was designed to do… protect itself from perceived famine.
The Hormonal Cost of Chronic Underfueling
When energy availability drops, the endocrine system is one of the first systems to respond.
The body begins downregulating processes that are not essential for immediate survival.
For female athletes, this may show up as:
- Irregular menstrual cycles
- Missing periods
- Reduced estrogen production
For male athletes, it may present as:
- Reduced testosterone
- Low libido
- Decreased recovery capacity
Beyond reproductive hormones, other systems are affected as well.
Athletes experiencing REDs may develop:
- Suppressed thyroid hormones
- Elevated cortisol levels
- Reduced leptin
- Changes in appetite regulation
- Altered glucose metabolism
These changes are not random. They represent the body’s attempt to conserve energy in response to chronic underfueling.
The Symptoms Clinicians Shouldn’t Ignore
One of the reasons REDs is so often missed is because many providers still rely heavily on body weight as a screening tool.
But athletes rarely walk into a clinic saying: “I think my resting metabolic rate is suppressed.”
Instead, they report symptoms such as:
- Fatigue
- GI issues
- Poor recovery
- Frequent illness
- Sleep disruption
- Anxiety
- Mood changes
- Persistent soreness
- Decreased performance
When viewed individually, these symptoms may appear unrelated. When viewed through a REDs-informed lens, they often tell a very different story.
A Case of REDs Hidden Behind Weight Stability
I once worked with a 42-year-old endurance athlete who came to me feeling exhausted.
She had spent years participating in marathons, hiking events, and ultramarathons while trying to navigate what she believed were normal age-related changes.
She reported:
- Irregular menstrual cycles
- Poor sleep
- Persistent fatigue
- Chronic GI symptoms
- Anxiety
- Difficulty recovering from training
Multiple healthcare providers had attributed her symptoms to perimenopause, stress, or simply getting older.
No one had assessed her fueling. No one reviewed her training demands. No one evaluated low energy availability.
When we took a deeper look, it all started to make sense.
Her labs revealed:
- Low ferritin
- Suppressed thyroid markers
- Low estradiol
- Low white blood cells
- Multiple indicators of chronic energy deficiency
Her weight had remained relatively stable throughout the process. Yet physiologically, her body was struggling.
After implementing a phased fueling approach and increasing energy availability, improvements began to emerge.
Her sleep and mood improved. Her laboratory values began normalizing. Most importantly, she finally understood that weight stability had never been proof of health.
Looking Beyond the Scale
The sports world has conditioned us to believe that body weight tells us everything we need to know about health.
But athletes are far more complex than a number on a scale.
Stable weight can coexist with:
- Hormonal dysfunction
- Metabolic suppression
- Impaired recovery
- Poor performance
- Low energy availability
This is why providers, coaches, and athletes must learn to look beyond weight and BMI when assessing health and performance.
The question is no longer: “What does the athlete weigh?”
The better question is: “How is the athlete functioning?”
Learn a Better Way to Assess Athletes
If you’re ready to move beyond weight-centric assessments and learn how to identify REDs before significant health consequences develop, I invite you to join the REDs Informed Provider Certification Program®.
Inside the program, you’ll learn how to:
✔️ Assess athletes using a systems-based approach
✔️ Recognize metabolic and hormonal adaptations to low energy availability
✔️ Screen for REDs across all body sizes
✔️ Use evidence-based assessment tools beyond BMI and body weight
✔️ Implement practical REDs care with confidence
This research-based certification program is designed for providers who want to better understand, assess, and support athletes experiencing REDs.
Join the LIVE cohort of the REDs Informed Provider Certification Program® and learn how to see what the scale cannot.