Dr. Stacy Sims is used to being told she can’t do something—she just never listens. From a young age, she learned how gender could shape, and sometimes limit, expectations. As a child in a U.S. military family, she once announced her dream of becoming a Navy SEAL or an Army Ranger. Her father, a colonel, told her she couldn’t. “You’re a girl,” he explained. That moment sparked a lifelong mission to challenge limits placed on women—not just in the military, but in science, sport, and health.
Now 51, Sims is a globally recognized expert in women’s health, exercise physiology, and nutrition science. Her research focuses on how the female body responds differently to training, diet, and hormonal changes—especially during menstruation and menopause. Her work has changed the way many women think about fitness and nutrition.
Her guiding principle? “Women are not small men.”
For decades, medical and scientific research was led by men—and focused on male bodies. Women were often excluded from studies due to the complexity of their hormonal cycles. As a result, most exercise and nutrition advice is based on male biology. Sims is working to change that.
Today, there’s growing awareness of the gap in women’s health research. Interest in menopause, in particular, is surging. The U.S. menopause market hit nearly US$17.7 billion in 2024 and is expected to grow to US$27.6 billion by 2033, according to Women’s Health Access Matters.
Sims has become one of the most prominent voices in this space. She has appeared on major platforms like The Diary of a CEO, The Mel Robbins Podcast, and the Huberman Lab, reaching millions of listeners. In just one month, her social media following grew by 100,000. She’s even inspired dozens of fake TikTok accounts in her name.
Despite the fame, Sims says the attention can be overwhelming. “There’s not enough of me,” she admits. “I want to give the information, but I don’t want people not to like me.” She describes herself as an “introverted extrovert” who prefers to stay behind the science.
Still, she isn’t afraid to spark debate. Her comments on cold plunging on The Mel Robbins Podcast caused a storm online. “I didn’t say women shouldn’t cold plunge,” she clarifies. “I said the science shows warmer temperatures are better for women.”
Sims holds positions at Stanford University and Auckland University of Technology. She also works with elite athletes in sports like cycling, triathlon, and Formula 1. Before she became an academic, she competed in ultra-running, bike racing, and triathlons.
She first moved to New Zealand in 1999 for a job opportunity, completed her PhD at the University of Otago, and later worked as a senior research fellow at the University of Waikato. In 2020, during COVID-19 lockdowns, she launched her own company. Through it, she offers courses, articles, and books on topics such as puberty in athletic girls, training during the menstrual cycle, and menopause in sports.
A typical day for Sims starts early—around 6:15 a.m.—balancing motherhood, workouts, meetings with international teams, and research. Living in Mt. Maunganui, she often works odd hours to stay in sync with overseas contacts. “It’s really stressful,” she says. “Late meetings for Europe, early ones for the U.S., and constant emails.”
Her path into science wasn’t straightforward. Sims spent much of her childhood in the Netherlands, speaking fluent French. She originally planned to study political science and work as a translator for the UN. But she struggled to stay awake in lectures. A roommate suggested she try exercise physiology—and she was hooked. “This is my jive,” she remembers thinking.
Her passion for women-specific science began while rowing at university. She noticed women on the team would mention being “off” during their periods. Meanwhile, the men seemed to improve more from the same training plans. “Why is that happening?” she wondered.
Sims also saw how female data was often dismissed in research. When she participated in studies, her results were sometimes discarded. “I was the only difference in the group—and they said that made my results invalid,” she recalls. “Then they’d say women’s results cause too many disruptions. But if there’s no difference, why throw mine out?”
Now the author of over 100 peer-reviewed studies, Sims often participates in her own research. Whether she’s stepping into a hot chamber or donating menstrual fluid for analysis, she believes it’s important to understand what participants go through. “Empathy is missing in science,” she says. “It affects outcomes. When participants know you’ve done the study too, they’re more likely to stick with it.”
Though there has been some progress, Sims says the system still needs major change. “Only 3% of sports medicine and nutrition research has been done properly on women,” she told her students during a recent Stanford lecture. She wants to see the scientific and medical world adopt a “female lens” in research and healthcare, offering care that truly supports women.
Why Ice Baths Aren’t Ideal for Women
Cold water immersion is a wellness trend promoted for its physical and mental benefits. While Sims agrees that cold exposure can help regulate blood sugar and improve nervous system function, she cautions that icy baths between 0–4°C can be too extreme for women. These temperatures can cause the body to react with intense stress, constrict blood vessels, and initiate shivering earlier than in men. Instead, women benefit more from cold water around 16°C—similar to ocean water during a New Zealand winter.
Sims prefers heat exposure for women, such as traditional Finnish saunas. She says heat helps both men and women with brain function, blood pressure, and gut health, but women tolerate heat better and longer.
Fasted Training Doesn’t Work the Same for Women
Training on an empty stomach—fasted training—is popular among fitness enthusiasts. While it may help some men, Sims says it can backfire for women. Because of their hormonal differences, women are already efficient at burning fat. Exercising without food can make the female brain believe the body is starving. This leads to stronger cravings for sugary foods later and a drop in daily activity due to fatigue.
“A small snack before a workout helps women control appetite and burn more calories overall,” Sims says. It doesn’t take much—just half a banana, a few spoonfuls of yogurt, or a protein coffee.
How Women Over 40 Should Train
Sims advises women over 40 to skip long cardio sessions and focus on short, intense workouts. She recommends three to four weekly sessions of heavy resistance training, 20–30 minutes each. Building muscle is key, especially during menopause, because muscle burns more calories at rest and supports metabolic health.
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