Learning from De Souza & Loucks
The scientists who discovered why under-eating—not exercise—causes athletes to lose their periods
The Story
For years, doctors blamed exercise for menstrual dysfunction in female athletes. "Train less," they'd say. "Your body can't handle the stress."
Anne Loucks proved them wrong.
Through elegant experiments at Ohio University, she demonstrated that exercise itself doesn't shut down the reproductive system. Under-eating does.
Mary Jane De Souza then translated this discovery into clinical practice, developing the "Female Athlete Triad" framework and creating the protocols that help athletes recover.
Together, they've changed how medicine approaches female athlete health.
Who are De Souza & Loucks?
| Scientist | Institution | Contribution |
|---|---|---|
| Anne Loucks | Ohio University | Discovered the "Energy Availability" mechanism; the 30 kcal threshold |
| Mary Jane De Souza | Penn State University | Created the Female Athlete Triad model; led clinical treatment trials |
Their work forms the scientific foundation for understanding Relative Energy Deficiency in Sport (RED-S).
What ISP Students Learn
Lesson 1: Energy Availability Is the Key Variable
Loucks developed a formula that explains everything:
Energy Availability (EA) = (Calories Eaten - Exercise Calories) ÷ Fat-Free Mass
This tells you how much energy is available for basic body functions AFTER accounting for training.
The threshold: When EA drops below 30 kcal/kg of fat-free mass per day, reproductive hormones shut down.
Your body interprets low energy availability as famine. In famine conditions, reproduction is a "luxury" function that gets shut off to conserve resources for survival.
"It's not the exercise. It's the failure to eat enough to cover the exercise."
What this means for young athletes: If you're training hard, you MUST eat more. Your body doesn't care that you're "trying to stay lean"—it responds to energy signals.
Lesson 2: A Missing Period Is a Medical Emergency
This is the most important lesson from their research:
Amenorrhea (loss of period) is not normal. It's not "what happens to serious athletes." It's a warning sign of under-fueling that predicts:
- Bone loss and stress fractures
- Immune suppression
- Hormonal dysfunction
- Cardiovascular problems
- Impaired performance
De Souza's research showed that even "regular" periods can hide problems. Up to 30% of athletes with monthly bleeding are actually anovulatory (not releasing eggs), indicating subclinical dysfunction.
What this means for young athletes: Getting your period isn't a hassle—it's proof your body is functioning. Losing it means something is wrong.
Lesson 3: The Fix Isn't Massive—But It Must Be Consistent
The REFUEL Study (led by De Souza) tested exactly how much extra food athletes needed to restart their cycles.
The answer: about 300-350 extra calories per day.
That's:
- A Greek yogurt + banana
- A peanut butter sandwich
- An extra substantial snack
The athletes who recovered gained only about 1.9 kg (4 lbs) on average. They didn't need to gain massive weight—they needed to close the energy gap consistently.
What this means for young athletes: Recovery from under-eating doesn't require dramatic changes. It requires consistent, adequate fueling.
Lesson 4: Carbohydrates Matter Specifically
Loucks discovered something important: the brain's "fuel sensor" specifically detects glucose availability.
Even if total calories are sufficient, severe carbohydrate restriction can trigger the same shutdown as overall under-eating. The brain interprets low carbs as "starvation" even if you're eating plenty of fat and protein.
This challenges trendy low-carb and keto approaches for female athletes. The reproductive system specifically needs to see adequate carbohydrate.
What this means for young athletes: Don't fear carbs. Your hormones need them.
Key Takeaways
| Lesson | One-Liner |
|---|---|
| Energy availability matters | EA below 30 kcal/kg FFM triggers shutdown |
| Missing periods are emergencies | It's a warning sign, not a badge of dedication |
| The fix is modest | ~300-350 extra calories daily can restore function |
| Carbs are necessary | Your reproductive system specifically monitors glucose |
How This Shows Up at ISP
De Souza and Loucks' research shapes how we approach athlete health in the Bio Skill Tree:
- Energy availability is taught as a critical health metric
- Menstrual health is part of female athlete education
- "Under-eating to stay lean" is identified as dangerous, not dedicated
- Adequate carbohydrate intake is emphasized for female athletes
When ISP coaches see warning signs of under-fueling, we respond with education and support—not praise for "dedication."
The Female Athlete Triad
De Souza's framework connects three related problems:
Low Energy Availability → Menstrual Dysfunction → Low Bone Density
These exist on a spectrum:
- Mild: Slightly low EA, subtle cycle changes, slightly reduced bone density
- Severe: Clinical eating disorder, amenorrhea, osteoporosis
The key insight: you don't have to be at the severe end to have problems. Subclinical dysfunction still causes damage.
Why Birth Control Pills Don't Fix It
Many doctors prescribe the pill to "give back" periods to amenorrheic athletes.
De Souza's research proved this doesn't protect bones. The synthetic hormones in pills suppress IGF-1 (a bone-building hormone), negating any benefit.
The real fix: Increasing energy availability (eating more). The period should return naturally—that's how you know the underlying problem is solved.
Learn More
"The athlete who loses her period isn't training too hard. She's eating too little."