Learning from Dr. Susan Kleiner
The nutritionist who proved "women are not small men"—and co-founded sports nutrition as a profession
The Story
In the 1980s, sports nutrition barely existed as a field. Athletes got their advice from coaches ("steak and eggs before games") or bodybuilding magazines (often wrong, sometimes dangerous).
Dr. Susan Kleiner helped change that.
As a co-founder of the International Society of Sports Nutrition (ISSN), she built the professional infrastructure that now governs the field. Her book Power Eating became the blueprint for strength and power athletes.
But her most important contribution might be simpler: she proved that female athletes have fundamentally different nutritional needs than males—and shouldn't be treated as "small men."
Who is Dr. Susan Kleiner?
| Credential | Detail |
|---|---|
| Education | PhD in Nutrition and Human Performance from Case Western Reserve University |
| Certifications | RD, FACN (Fellow of the American College of Nutrition), CNS, FISSN (co-founder) |
| Teams | Seattle Storm (WNBA champions), Cleveland Cavaliers (NBA), Seattle Seahawks (NFL) |
| Known For | Power Eating; The Good Mood Diet; female athlete nutrition research |
Kleiner bridges academic rigor and elite sports—bringing research to the locker room.
What ISP Students Learn
Lesson 1: Eat for Output, Not Restriction
The "Power Eating" philosophy flips the script on diet culture.
Traditional approach: "How little can I eat?"
Kleiner's approach: "How do I fuel performance?"
| Old Mindset | Power Eating Mindset |
|---|---|
| Food is the enemy | Food is the tool |
| Restrict to lose weight | Fuel to build power |
| Count calories | Time nutrients |
The insight: Athletes who restrict food often get the opposite of what they want—less muscle, more fat, worse performance. Athletes who fuel strategically get leaner AND stronger.
What this means for young athletes: Think about what food DOES for you, not just what it weighs.
Lesson 2: Carbs Are Not the Enemy
In an era of low-carb trends, Kleiner defends carbohydrates for power athletes:
The science: The glycolytic pathway (which powers efforts lasting 30 seconds to 2 minutes) runs exclusively on glucose. Without carbs, you can't fuel high-intensity work.
The warning: Without adequate carbohydrates, athletes feel like they're working hard—but their actual output is "mediocre." The brain governs down neural drive to protect limited fuel.
Kleiner's recommendation: Up to 2g of carbohydrate per pound of lean body mass for muscle building.
What this means for young athletes: Don't fear carbs. Fear low energy.
Lesson 3: Women Are Not Small Men
For decades, sports nutrition research excluded women because the menstrual cycle was a "confounding variable." Kleiner called this "pure laziness" and dedicated her career to female-specific nutrition.
Her key finding: Hormonal fluctuations fundamentally alter how women use fuel.
| Phase | What Happens | Nutritional Implication |
|---|---|---|
| Luteal (high hormone) | Progesterone raises body temperature, increasing metabolic rate by ~300 kcal/day | EAT MORE—despite feeling bloated |
| Luteal | Liver's gluconeogenesis suppressed | MORE reliant on carbs during exercise |
| Follicular (low hormone) | Physiology more similar to males | Can moderate carbs slightly |
The counter-intuitive advice: When women feel bloated and want to restrict (PMS), they should actually eat MORE.
What this means for young female athletes: Track your cycle. Adjust your fueling to your phase, not despite it.
Lesson 4: Hydration Is the Forgotten Performance Enhancer
Kleiner's research shows that a fluid loss of just 2% of body weight triggers:
- Fuzzy short-term memory
- Difficulty focusing
- Reduced performance capacity by up to 21%
- Reduced aerobic capacity by nearly 50%
Her protocol:
| Timing | What to Do |
|---|---|
| Pre-exercise | 3-5 cups over 2-3 hours before; another 1/2-1 cup 15-20 min before |
| During | 1/2-1 cup every 15-20 minutes |
| After | 16-24 oz for every pound of weight lost |
The key insight: Don't wait until you're thirsty—by then, performance is already impaired.
What this means for young athletes: Weigh yourself before and after practice. Replace 150% of what you lost.
Key Takeaways
| Lesson | One-Liner |
|---|---|
| Fuel for output | Eat to perform, not just to manage weight |
| Carbs power intensity | Glycolytic work requires glucose |
| Women differ | Menstrual cycle affects fuel utilization |
| Hydrate proactively | 2% loss = significant impairment |
How This Shows Up at ISP
Dr. Kleiner's "Power Eating" philosophy shapes the Bio Skill Tree:
- We teach eating FOR performance, not just to manage weight
- Female-specific nutrition is integrated, not ignored
- Hydration protocols are taught with specific volumes and timing
- The connection between fuel and mood is emphasized
When ISP students think about nutrition, they think about power and performance.
The Good Mood Diet
Kleiner's research extends beyond muscles to the brain:
The serotonin-carbohydrate link: Carbohydrates help tryptophan cross the blood-brain barrier, where it becomes serotonin (the "feel-good" neurotransmitter).
The implication: Low-carb diets can strip the brain of serotonin, causing irritability, brain fog, and depression.
For athletes whose mental game matters, this is critical information.
The 30% Fat Floor
Kleiner advocates for fat intake at approximately 30% of total calories.
Why not less?
- Fats are required for vitamin absorption (A, D, E, K)
- Fats are required for hormone synthesis (testosterone, estrogen)
- Very low-fat diets crash hormone levels
The sources: Mono- and polyunsaturated fats—avocados, nuts, olive oil, fatty fish—for inflammation control.
Learn More
"Most diets cause chemical changes in the brain that make the dieter feel depressed. For an athlete, this state is unacceptable."