For many athletes, body fat has become something to fear. It’s often viewed as unnecessary weight… something to reduce in the pursuit of better performance.
The message is everywhere:
“Leaner is faster.”
“Less body fat equals better performance.”
“If I could just lose a little more body fat…”
But here’s what many athletes aren’t told:
Body fat hormones play a critical role in regulating health, recovery, and athletic performance.
Body fat isn’t simply stored energy. Adipose tissue is a metabolically active endocrine organ that produces hormones influencing metabolism, reproductive health, bone health, appetite, and energy availability.
When body fat becomes too low, or when an athlete experiences chronic low energy availability, the body’s hormonal systems begin adapting to conserve energy. These adaptations are at the core of REDs and can affect nearly every system in the body.
Understanding how body fat hormones work can completely change the way we think about athlete health. Instead of seeing body fat as something to eliminate, we can begin to recognize its essential role in supporting recovery, resilience, and long-term performance.
Body Fat Does More Than Store Energy
For years, adipose tissue was thought to function primarily as the body’s energy reserve. Now, we know a lot more. Adipose tissue is an endocrine organ, meaning it produces hormones and signaling molecules that communicate with nearly every system in the body.
These hormones help regulate:
- appetite
- metabolism
- reproductive function
- immune function
- inflammation
- bone remodeling
- energy balance
In other words, body fat is not biologically “inactive.”
It is constantly communicating with the brain and the rest of the body about whether there is enough energy available to support normal physiological function.
Leptin: The Hormone That Connects Body Fat and the Brain
One of the most important hormones produced by adipose tissue is leptin. Think of leptin as the body’s energy messenger.
As body fat and energy availability change, leptin communicates those changes to the hypothalamus, the part of the brain responsible for regulating many essential physiological processes.
When energy stores are sufficient, leptin signals:
“We have enough energy available.”
When body fat or energy availability decline, leptin levels decrease.
That message tells the brain:
“Resources are limited.”
The brain then begins making adjustments to conserve energy. These adaptations are not a mistake… they are survival mechanisms.
How Low Leptin Triggers the REDs Cascade
Leptin doesn’t work in isolation.
Lower leptin levels influence multiple hormonal systems throughout the body.
As leptin declines, the brain may begin downregulating:
- reproductive hormones
- thyroid hormones
- metabolic rate
- bone formation
- appetite regulation
This is one reason REDs affects so many different body systems simultaneously.
What begins as inadequate energy availability eventually becomes a coordinated endocrine response designed to protect survival.
Unfortunately, those same adaptations often impair athletic performance and long-term health.
Body Fat Supports Reproductive Health
One of the most recognized consequences of chronic low energy availability is disruption of reproductive hormones.
For female athletes, this may include:
- irregular menstrual cycles
- loss of menstrual periods
- decreased estrogen production
For male athletes, it may include:
- reduced testosterone
- decreased libido
- impaired recovery
These changes are often viewed as isolated reproductive issues.
In reality, they represent the body’s response to insufficient available energy.
When the brain perceives energy scarcity, reproduction becomes a lower priority.
Body fat and the hormones it produces help communicate whether conditions are favorable for maintaining normal reproductive function.
Body Fat Helps Protect Bone Health
Many athletes associate stronger bones with calcium and vitamin D.
Those nutrients are certainly important, but healthy bones also depend on adequate energy availability and normal hormone production.
When estrogen, testosterone, leptin, and other hormones decline, bone remodeling slows.
Bone breakdown may begin exceeding new bone formation.
Over time, athletes become more vulnerable to:
- bone stress injuries
- stress fractures
- decreased bone mineral density
- osteoporosis later in life
This is one reason REDs can have consequences long after an athlete’s competitive career has ended.
Body Fat Influences Mood, Recovery, and Overall Health
The effects of low body fat and chronic low energy availability extend beyond bones and reproductive hormones.
Athletes may also experience:
- persistent fatigue
- brain fog
- mood changes
- irritability
- anxiety
- poor sleep
- slower recovery
- increased illness
These symptoms are often viewed separately, but they typically stem from the same underlying physiological adaptation.
When energy becomes limited, the body begins reallocating resources toward immediate survival. Functions that support long-term health and optimal performance become secondary.
Why Lower Body Fat Isn’t Always Better
In sport culture, body fat is often treated as something to minimize.
But physiology doesn’t work that way.
Every athlete has a range in which their body can:
- fuel training
- recover effectively
- maintain hormonal health
- build bone
- adapt to exercise
- support immune function
- perform consistently
Trying to push below that range may not improve performance.
Instead, it may increase the risk of REDs and compromise the very systems athletes depend on.
Body Fat Is Only One Piece of the Performance Puzzle
Body composition matters, but not for the reasons many athletes believe.
The goal isn’t achieving the lowest possible body fat percentage.
The goal is supporting a body that is healthy enough to train consistently, recover fully, and perform at its highest potential.
An athlete with slightly higher body fat but excellent fueling, recovery, hormonal function, and resilience will often outperform an athlete who is chronically underfueled in pursuit of an arbitrary number.
Performance isn’t determined by body fat alone. It’s determined by how well the entire system functions.
Why Body Fat Hormones Matter for Athlete Health
For too long, body fat has been viewed as the enemy of athletic performance.
In reality, body fat plays an essential role in maintaining hormonal health, supporting recovery, protecting bone health, regulating metabolism, and signaling that enough energy is available for the body to function optimally.
Without adequate body fat, and more importantly, without adequate energy availability, the body begins making hormonal adaptations designed to conserve energy.
Those adaptations may help ensure survival.
But they often come at the expense of health and performance.
Rather than asking:
“How can I lose more body fat?”
A better question is:
“Does my body have the energy it needs to perform, recover, and thrive?”
Learn to Assess Athletes Beyond Body Fat
If you’re ready to move beyond outdated conversations about body fat and learn how to assess athletes through a comprehensive, REDs-informed lens, I invite you to join the REDs Informed Provider Certification Program®.
Inside the program, you’ll learn how to:
✔️ Understand the hormonal adaptations of low energy availability
✔️ Assess athletes beyond body composition and BMI
✔️ Recognize early signs of REDs across all body sizes
✔️ Interpret laboratory markers through a REDs-informed lens
✔️ Apply evidence-based strategies to support athlete health and performance
This research-based program equips providers with the knowledge and tools to care for the whole athlete, not just their body composition.
Join the REDs Informed Provider Certification Program® and learn how to see body fat as part of physiology, not the enemy.