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What it argues
Roar is exercise physiologist Stacy Sims's argument that women are not small men, and that decades of sports science research conducted primarily on male subjects has produced nutrition and training advice that is systematically wrong for women. Sims spent years as a researcher at Stanford and AUT (Auckland University of Technology) studying female physiology and how the menstrual cycle affects performance, recovery, and nutritional needs. The book translates that research into practical guidance for active women at every level.
The core insight is hormonal: estrogen and progesterone fluctuate across the menstrual cycle in ways that profoundly affect fuel utilization, hydration, training adaptation, and recovery. In the follicular phase (the first half of the cycle, dominated by estrogen), women burn more carbohydrate, recover faster, and adapt better to hard training — this is the time for high-intensity work and personal records. In the luteal phase (the second half, dominated by progesterone), the body is more catabolic, burns more protein, retains more heat, and performs less well at high intensity but tolerates moderate endurance work better. Training and nutrition that ignores these phases is essentially fighting the body's biology.
What it gets right
- 1.
Women's exercise physiology differs from men's in ways that make much standard sports nutrition and training advice either suboptimal or actively harmful for female athletes.
- 2.
The menstrual cycle creates two distinct physiological phases with different fuel preferences, recovery capacities, and training adaptability — scheduling training and nutrition to match these phases improves results.
- 3.
During the follicular phase (high estrogen), women perform better at high-intensity efforts and recover faster; during the luteal phase (high progesterone), intensity should typically be moderated.
What it covers
Who wrote it
Stacy Sims is an exercise physiologist and nutrition scientist who has spent over two decades researching female physiology, particularly in the context of sport and performance. She earned her PhD from the University of Otago and has held positions at Stanford University and Auckland University of Technology. Her research has been published in peer-reviewed journals including The Lancet and Medicine and Science in Sports and Exercise. She is also the author of Next Level, which applies the Roar framework specifically to perimenopausal and menopausal women. Sims consults with elite athletes, national teams, and the U.S. Olympic and Paralympic Committee.
