Exercise & Nutrition Scientist: The Truth About Exercise On Your Period! Take These 4 Supplements!

Dr. Stacy Sims, an exercise physiologist and nutrition scientist, discusses fundamental sex differences in human physiology that have been overlooked in medical research and sports science. She explains that women are born with more endurance-type muscle fibers while men have more fast-twitch fibers, giving men greater anaerobic capacity and power output. At puberty, these differences expand significantly: girls' hips widen, changing their knee-to-hip angle (Q angle), which increases ACL tear risk 3-4 times higher than men. This biomechanical change, combined with lack of education, causes over 60% of previously athletic girls to drop out of sports by age 14.

Sims emphasizes that sports science research has historically relied on male subjects because recruitment strategies and study designs favor men, and most researchers and principal investigators are male. She recounts how her own research data was discarded in graduate school because it didn't match male results, leading her to discover the menstrual cycle's profound impact on physiology.

On nutrition, Sims explains that women's hypothalamus is more sensitive to nutrient density than men's, meaning women require more frequent food intake to prevent the body from entering a stress state. The baseline calorie requirement for metabolic health is 30 calories per kilogram of fat-free mass for women versus 15 for men. This explains why fasted training and calorie restriction work for men but harm women, causing lean muscle loss and metabolic dysfunction. She advocates against popular fasting protocols for women, recommending instead an overnight fast (eating dinner 2-3 hours before bed, then eating within 30 minutes of waking) to blunt cortisol peaks.

Regarding the menstrual cycle, Sims details how the follicular phase (days 1-13) offers robust immune function and resilience to training stress, while the luteal phase (days 14-28) brings increased insulin resistance and higher carbohydrate/protein needs due to progesterone's effects. Women's core temperature rises 0.5°C after ovulation, reducing heat tolerance. She recommends women track their "sessional rating of perceived exertion" rather than rigidly following cycle phases, as anovulatory cycles are increasingly common.

On supplements, Sims recommends: (1) Creatine at 3-5g daily (not the bodybuilding loading protocol) for gut health, brain health, and muscle performance; (2) Vitamin D3 for every body system; (3) Omega-3s, especially entering perimenopause; and (4) Iron supplementation every other day for women with ferritin below 50, despite lab reference ranges showing 26 as "normal"—she argues reference ranges have shifted to reflect sicker populations.

For cold and heat exposure, Sims reveals sex differences: women need 15-16°C water (versus 0-4°C for men) to experience equivalent cold plunge benefits, and women require longer sauna sessions (20-30 minutes versus men's shorter times) to achieve the same cardiovascular adaptations. She explains this is due to women's greater subcutaneous fat and different vasodilation patterns.

On exercise during perimenopause and menopause, Sims emphasizes that women can no longer rely on hormones for muscle protein synthesis and bone density, requiring external stress through high-intensity interval training, plyometrics, and resistance training 3x weekly. She notes resistance training is crucial for mobilizing abdominal fat and increasing myokines that signal the liver to use free fatty acids rather than storing them as visceral fat.

Sims addresses contraception and menopause misconceptions, arguing that hormone therapy for menopause should be called "menopause hormone therapy" (not HRT) because it's a therapy to attenuate change, not replace hormones to stay young. She notes there's no evidence hormone therapy prevents dementia, contrary to popular claims. She also criticizes prescribing oral contraceptives to teenage girls with irregular cycles without investigating underlying causes.