“Women are not small men.” This is a common line you’ll hear from me, Dr. Stacy Sims, a female-focused sports scientist and educator. But what does it mean? And why is it shaking up the health and fitness industry?
For years, women have been unknowingly listening to male-centered data: “Fasting is good,” “The keto diet works wonders,” “Carnivore diets are amazing.” Sure, you might feel great temporarily, but at what cost? We’re only just starting to uncover the truth—the majority of these studies were conducted by men, on men, because in research, men are considered the default human. Anything else? An anomaly (Shepard, 2023).
Far too many women are struggling: struggling to fall pregnant, struggling with fatigue, losing their periods, experiencing low energy availability (LEA), and facing relative energy deficiency in sport (RED-S). I’ve been there myself. I trained fasted because I was told it would make me lean and strong. I lost my period for a year. Why? Because the information guiding me was not meant for me—not for women.
Would you ask a weightlifter how to fuel for an ultra-marathon? No. Because different demands require different approaches. The same applies to women vs. men in training, recovery, and nutrition. If we want to age well, go through menopause with grace, avoid being crippled by our period, and feel energized every day, we need to wake up and smell the coffee (but not on an empty stomach).
Understanding Female Physiology
Women are more hormonally intricate than men. Our physiology shifts daily due to the menstrual cycle. We move through two main phases: the Follicular Phase (days 1–14) and the Luteal Phase (days 14–28).
- Follicular Phase: Estrogen rises as follicles in the ovaries mature. During this time, we’re building and breaking down tissue. This phase benefits from higher carbohydrate and protein intake to support tissue regeneration and training.
- Luteal Phase: Estrogen and progesterone peak and then fall if no fertilization occurs, triggering menstruation. Progesterone, in particular, increases resting heart rate, decreases heat tolerance, and slows down recovery. This phase requires more energy, especially from fats and proteins.
Studies (Wohlgemuth et al., 2021) show that estrogen is linked to serotonin, so during the Follicular Phase, mood often improves. Ovulation makes women more stress-resilient, so it’s a great time to push intensity and resistance training (Sims, as cited in WHOOP, n.d.).
In contrast, the Luteal Phase demands a different approach: lower intensity, more recovery. Progesterone increases your basal metabolic rate by up to 10%. Appetite follows, and that’s okay. Your body needs fuel.
Nutrition: Phase by Phase
Let’s break it down:
Follicular Phase:
- Carbohydrates: The AMDR recommends 45–65% of your daily intake from carbs, or 6–10g/kg for performance athletes (Clear Creek Wellness, n.d.).
- Protein: Supports muscle recovery and hormone production (Cleveland Clinic, 2023).
- Fats: Crucial for hormone synthesis. Reducing fat intake may lengthen the follicular phase and impair performance.
Ovulatory Phase:
- Complex Carbs: Sweet potatoes, whole grains, rice—needed for brain signaling during ovulation (Fiona Lawson, n.d.).
- Protein: Demand increases due to hormonal fluctuations (PubMed, 2013).
Luteal Phase:
- Higher Metabolic Rate: Fuel with more calories, particularly carbs.
- Fat & Protein Oxidation: Increases, so dietary fats and proteins are essential (Marolo, 2023).
Hydration is key throughout. Aim for at least 1.5L per day and more if you’re active. Whole, minimally processed foods are ideal. Carbs are not the enemy; they’re the foundation of hormonal health. Low energy availability tells the hypothalamus to downregulate hormone production. That means missed periods and infertility (Sims, 2023).
The Exercise Conundrum
Exercising as a woman isn’t as simple as “move more.” Society tells us to be skinny, but not too skinny; fit, but not muscular; curvy, but not fat. Unsurprisingly, most women will struggle with food or exercise at some point.
Christine Yu notes that our bodies need 1,500 to 2,000 calories just to function. Want to do more than just exist? Ride horses, run, win competitions? You need to fuel that ambition.
Carbohydrate Myths:
Carbs have been demonized thanks to studies largely done on men. That’s why men see gym gains while women experience amenorrhea, bone stress injuries, and infertility (Easter, 2023).
RED-S and LEA
Low Energy Availability (LEA) means your intake doesn’t meet your output. It’s the root cause of Relative Energy Deficiency in Sport (RED-S) (Manore, 2017). And yes, it can happen even if you’re eating what seems like “a lot.” Doctors dismissed my period loss as “normal.” No one assessed my nutrition.
RED-S might not seem catastrophic initially—maybe you look the way you’ve always wanted. But under the surface? Frequent illness, injuries, metabolic disruption, and increased risk of eating disorders. This needs to be openly discussed.
The Problem with Fasted Workouts
Fasted workouts are a form of stress. Add them to an already stressed system, and you spike cortisol. Over time, this disrupts your hormonal balance and leads to burnout, injuries, and even muscle loss.
Even something as simple as a protein coffee or small snack (like toast or dates) before training can curb cortisol spikes and improve performance (Huberman & Sims, 2024).
Rule of thumb:
- If training <1 hr: small carb snack ~30 min prior.
- Morning training: women need 30g carbs. Men can train fasted. Women can’t.
- Post-workout: Eat! Glycogen must be replenished for proper recovery (Derwent, 2021).
Supplements
Be wary of marketing, but some supplements genuinely support female health:
- Creatine: Women have 70–80% lower stores. It’s great for short bursts of high-intensity training. It also supports brain health, menstrual health, and post-menopausal energy (Sims, 2024).
- Iron: Vital during menstruation and especially in women with RED-S.
- Vitamin D & Calcium: Essential for bone health, particularly in endurance athletes (Kunz, 2021).
Female Equestrian Athlete Example
Take Chloe, a 22-year-old equestrian athlete. She rides 1–3 horses daily, aims for 2,000+ calories, prioritizes carbs for endurance, and practices cycle syncing.
Menstrual Phase (Day 1):
- Iron-rich foods: leafy greens, lean meats, legumes.
- Vitamin B: whole grains, eggs, dairy.
- Omega-3s: fatty fish, seeds.
- Magnesium: dark chocolate, avocados.
Dr. Sims’ Tip: This is actually a great time to train! Recovery is enhanced, and carbs are more accessible.
Late Follicular Phase:
- Balanced diet for egg maturation.
- Example breakfast: gluten-free toast, avocado, chicken livers, fruit, and pumpkin seeds.
Ovulatory Phase:
- High fiber and antioxidant-rich foods: berries, leafy greens, quinoa.
- Example breakfast: quinoa porridge with berries, kiwi, nuts, eggs.
Luteal Phase:
- Focus on Vitamin B and healthy fats: avocado, seeds, fatty fish.
- Combat bloating and mood swings with nutrient-dense, high-carb meals.
- Example breakfast: warm oats with egg whites, topped with fruit and seeds.
Final Words
I hope this opens your eyes to the complexity of female physiology. We need more female-centric sports science. Step 1? Support women’s sports. Show up, stream, cheer. That brings funding. That brings research. And that brings change.
Athletes and coaches: educate yourselves. Then educate others. Listen to the podcasts. Read the books. Be the change.
Because remember: women are not small men. And it’s time the world acted like it.