While menstrual dysfunction is certainly an important warning sign, it’s only one piece of a much larger physiological puzzle.
REDs isn’t simply a reproductive hormone disorder. It’s a whole-body adaptation to prolonged low energy availability, affecting nearly every endocrine system in the body.
When the brain senses there isn’t enough energy to support both survival and performance, it begins making strategic decisions about where energy should and shouldn’t be spent.
Hormones are often the first systems to change.
Understanding these hormonal adaptations helps explain why athletes with REDs experience symptoms that seem unrelated at first glance, from fatigue and poor recovery to recurrent injuries, mood changes, and declining performance.
The Endocrine System Is Trying to Protect You
Hormones act as the body’s communication network.
They regulate nearly every physiological process, including:
- metabolism
- reproduction
- bone remodeling
- recovery
- mood
- sleep
- appetite
- stress response
- body temperature
When energy availability remains low for an extended period, the brain recognizes that resources are limited.
Rather than maintaining normal hormone production, it begins conserving energy.
This isn’t a malfunction, it’s a survival response… the body doing what it’s supposed to do.
Unfortunately, survival and optimal athletic performance are not always the same thing.
Thyroid Hormones: Slowing the Metabolic Engine
One of the earliest hormonal adaptations seen in REDs involves the thyroid.
The active thyroid hormone, triiodothyronine (T3), often decreases as energy availability declines.
T3 helps regulate:
- resting metabolic rate
- body temperature
- energy expenditure
- protein synthesis
- normal cellular function
When T3 falls, athletes may experience:
- persistent fatigue
- feeling cold frequently
- sluggish recovery
- decreased training adaptations
- constipation
- lower resting metabolic rate
This isn’t because the thyroid is “broken.”
It’s because the body is intentionally reducing energy expenditure to conserve fuel.
In some athletes, TSH and T4 may remain within normal laboratory ranges, making the decline in T3 easy to overlook if providers aren’t viewing labs through a REDs-informed lens.
Cortisol: When Stress Never Turns Off
Cortisol often gets labeled the “stress hormone,” but its role is much broader.
It helps regulate:
- blood glucose
- inflammation
- immune function
- recovery
- energy availability
Training itself is a healthy stressor.
The problem arises when hard training is combined with inadequate fueling.
Without enough energy to support recovery, cortisol can remain elevated for longer periods of time.
Chronically elevated cortisol has been associated with:
- impaired recovery
- increased muscle breakdown
- sleep disturbances
- decreased immune function
- mood changes
- reduced bone formation
Athletes often describe this as feeling “tired but wired.”
They’re exhausted, yet struggle to fully recover.
Reproductive Hormones: The System Most People Recognize
The reproductive system is one of the first systems the body downregulates when energy becomes scarce.
For female athletes, this may include:
- irregular menstrual cycles
- absent menstrual periods
- low estrogen
- disrupted ovulation
For male athletes, chronic low energy availability may contribute to:
- lower testosterone
- reduced libido
- decreased muscle protein synthesis
- reduced recovery capacity
These hormonal changes aren’t random.
From the body’s perspective, reproduction is not essential for immediate survival.
If there isn’t enough energy available to support normal physiological function, reproduction becomes a lower priority.
Leptin: The Hormone That Signals Energy Availability
One of the most important hormones discussed in REDs is leptin.
Produced primarily by adipose tissue, leptin communicates the body’s energy status to the brain.
When energy availability is adequate, leptin tells the brain, “we have enough resources.”
When energy availability declines, leptin levels fall.
This change contributes to many of the downstream hormonal adaptations seen in REDs.
Lower leptin signaling can influence:
- reproductive hormone production
- thyroid function
- appetite regulation
- bone metabolism
- metabolic rate
Leptin acts as one of the body’s earliest indicators that energy conservation measures should begin.
The Brain Feels It Too
Hormonal changes don’t just affect physical performance. They affect the brain.
Many athletes experiencing REDs report:
- increased anxiety
- depressed mood
- irritability
- difficulty concentrating
- brain fog
- poor sleep
These symptoms are often blamed on stress, school, work, or overtraining.
In reality, neuroendocrine changes associated with low energy availability may be contributing significantly.
The brain is one of the body’s highest energy-consuming organs.
When energy is limited, cognitive and emotional functioning can be affected as well.
Bone Health: The Hormonal Consequence That Can Last for Years
One of the most concerning consequences of hormonal disruption is impaired bone health.
Bone is constantly being remodeled.
This process depends on adequate energy availability and healthy hormone production.
When estrogen, testosterone, IGF-1, leptin, and thyroid hormones decline while cortisol remains elevated, bone formation slows.
Over time this can increase the risk for:
- bone stress injuries
- stress fractures
- reduced bone mineral density
- osteoporosis later in life
This is why REDs is never “just about performance.”
Its consequences can extend well beyond an athlete’s competitive years.
The Hidden Hormone Cascade
| Hormone/System | What Happens in REDs | Common Signs & Symptoms |
| T3 (Thyroid) | Decreases to conserve energy | Fatigue, feeling cold, slowed metabolism, constipation |
| Cortisol | Often remains elevated | Poor recovery, sleep disruption, anxiety, muscle breakdown |
| Estrogen/Testosterone | Production decreases | Menstrual dysfunction, low libido, impaired recovery |
| Leptin | Decreases with low energy availability | Hormonal downregulation, altered appetite, metabolic adaptation |
| Neuroendocrine System | Brain adapts to conserve energy | Brain fog, mood changes, poor concentration |
| Bone Remodeling | Bone formation decreases | Stress fractures, reduced bone density |
Looking Beyond Missing Periods
One of the greatest misconceptions about REDs is that hormonal dysfunction begins and ends with menstrual health.
It doesn’t.
REDs creates a cascade of hormonal adaptations affecting nearly every system in the body.
- Fatigue.
- Poor recovery.
- Sleep disruption.
- Mood changes.
- Recurrent injuries.
- Difficulty concentrating.
- Low libido.
- Feeling cold all the time.
These symptoms are often connected.
When viewed through a REDs-informed lens, they tell the story of a body working incredibly hard to survive on insufficient energy.
Learn to Recognize the Full Hormonal Picture
Understanding REDs means looking beyond one hormone or one symptom.
It requires recognizing how the endocrine system adapts as a whole when energy availability becomes insufficient.
Inside the REDs Informed Provider Certification Program®, we take a systems-based approach to understanding REDs so you can identify these physiological adaptations before they progress.
You’ll learn how to:
✔️ Interpret hormonal adaptations through a REDs-informed lens
✔️ Understand how low energy availability affects multiple endocrine systems
✔️ Recognize non-stereotypical presentations of REDs
✔️ Assess athletes beyond weight, BMI, and menstrual status
✔️ Implement evidence-based strategies to support recovery and long-term athlete health
If you’re ready to move beyond symptom-based care and better understand the physiology behind REDs, I’d love to have you join the REDs Informed Provider Certification Program®.