Women are not small men. They have different bodies, different needs.
For generations, medicine built its map of the human body using only half the population as its guide, then handed that map to everyone. Dr. Stacy Sims, an exercise physiologist working in New Zealand, has spent her career charting the territory that was left blank — the distinct hormonal, metabolic, and physiological landscape of women's bodies. Her work arrives at a moment when science is slowly reckoning with the cost of its own blind spots, and when the question of what it means to care for a body is finally being asked with the full range of human bodies in mind.
- Decades of medical research built on male subjects has left women following fitness and nutrition advice that was never actually tested on them — a quiet but consequential form of exclusion.
- Women's bodies respond to exercise differently: after intense effort, blood pools outward rather than returning to the heart, causing dizziness that a cold drink post-workout can help correct.
- Popular trends like intermittent fasting and Zone 2 cardio were developed largely on men and can actively work against women's physiology rather than supporting it.
- Women approaching menopause face accelerated muscle loss and fat gain a decade or more before men experience similar shifts, making strength training and high-intensity intervals especially urgent — not optional.
- Protein recommendations for women still trace back to studies of elderly men; Sims argues women need up to 1.1 grams per pound of body weight daily, with precise timing around workouts to preserve muscle.
- A 2024 executive order and a 2016 NIH policy signal institutional momentum, but compliance remains uneven — many studies that include women still fail to analyze their data separately by sex.
For decades, medical researchers studied men, published their findings, and applied those conclusions to women — assuming a smaller body was simply a scaled-down version of a larger one. The consequences have been lasting. Women received incomplete guidance about their hearts, muscles, and nutritional needs, often without knowing the advice they followed was never tested on them.
Despite a 2016 NIH policy requiring sex to be considered as a variable in research, a 2022 analysis found women remain underrepresented in medical literature, and many studies that did include women failed to analyze their data separately by sex. The problem traces back to the founding of modern science, when women were excluded from laboratories and male researchers never questioned whether their findings applied universally.
Dr. Stacy Sims, an exercise physiologist and nutrition scientist based in New Zealand, has built her career around a deceptively simple premise: women are not small men. Their hormonal profiles, recovery mechanisms, and metabolic responses to exercise and food differ in ways that matter. The COVID-19 pandemic made this undeniable — men faced worse acute outcomes, while women suffered more severe vaccine side effects and more debilitating long COVID, forcing researchers to confront differences they had long ignored.
On exercise, Sims argues women should prioritize strength training and high-intensity intervals over the steady moderate cardio long recommended to them. Women's bodies are already well-suited for endurance; what they need is the metabolic and neurological benefits of resistance work and true high-intensity bursts. This becomes especially urgent around perimenopause, when hormonal shifts between ages 40 and 50 accelerate muscle loss and fat gain — changes men typically don't face until decades later.
Recovery differs too. After hard effort, men's blood vessels constrict, pushing blood back to the heart. Women's vessels dilate, causing blood to pool outward — which is why dizziness after intense exercise is common. Drinking something cold immediately afterward helps redirect circulation and speeds recovery.
Nutrition guidance has fared no better. Current protein recommendations for women derive from studies of elderly men. Sims recommends one to 1.1 grams of protein per pound of body weight daily, with specific amounts timed around both strength and cardio sessions — and higher targets for women in perimenopause, whose bodies grow more resistant to the muscle-building effects of both exercise and protein.
The fitness trends dominating popular culture — intermittent fasting, Zone 2 training — were largely developed and tested on men. Most people never think to ask which population a trend was studied on. Sims's work is an effort to change that. In 2024, as President Biden signed an executive order aimed at improving women's health research across federal agencies, the question of what works specifically for women has finally begun receiving the attention it has long been owed.
For decades, the medical establishment built its understanding of human health on a foundation of male bodies. Researchers studied men, published their findings, and then applied those conclusions to women—assuming that a smaller body was simply a scaled-down version of a larger one. The consequences of this assumption have been profound and lasting. Women have received incomplete advice about their hearts, their muscles, their recovery, and their nutritional needs, often without knowing that the guidance they followed was never actually tested on them.
This gap in medical knowledge persists even now. A 2022 analysis found that women remain broadly underrepresented in medical literature, and despite a 2016 policy from the National Institutes of Health requiring researchers to consider sex as a variable in their studies, the results have been mixed. Many studies that did begin including women failed to actually analyze their data separately by sex, rendering the inclusion largely meaningless. The problem runs deep: it traces back to the founding of modern science itself, when women were excluded from laboratories and lecture halls, and male researchers simply did not question whether their findings applied universally.
Dr. Stacy Sims, an exercise physiologist and nutrition scientist based in New Zealand, has spent her career documenting how women's bodies actually work—and how they differ from men's in ways that matter for fitness and health. Her central insight is simple but radical: women are not small men. They have different hormonal profiles, different recovery mechanisms, different metabolic responses to exercise and food. The COVID-19 pandemic, paradoxically, helped make this case. The virus hit men harder, yet women experienced more severe vaccine side effects and more debilitating long COVID, including greater cognitive effects. Suddenly, researchers had to confront sex differences they had long ignored.
When it comes to exercise, Sims argues that women should prioritize strength training and high-intensity intervals over the steady, moderate-intensity cardio that has long been recommended to them. Women's bodies are naturally suited for endurance work—they can already go long and slow. What they need instead is the metabolic boost and brain protection that comes from resistance training and true high-intensity bursts of 30 seconds to one minute. This matters especially as women approach menopause, when hormonal shifts between ages 40 and 50 trigger rapid muscle loss and fat gain. Strength training slows that decline and protects bone density and balance—changes that don't typically affect men until their late 50s or 70s.
Recovery from exercise looks different in women's bodies too. After a hard workout, men experience vasoconstriction—their blood vessels tighten, pushing blood back toward the heart for rapid recovery. Women experience vasodilation, the opposite: blood pools in the periphery, which is why they often feel lightheaded or dizzy after intense exercise. A simple fix exists: drinking something cold immediately after exercise helps redirect that blood back to the center of the body and speeds recovery.
Nutrition presents another area where women have been given inadequate guidance. The recommended daily protein intake for women is based on studies of 70- to 80-year-old men—a population that bears little resemblance to most women. In reality, women should aim for one to 1.1 grams of protein per pound of body weight daily. For strength training, they should consume 15 grams before a session and 30 to 35 grams after. For cardiovascular work, 15 grams of protein paired with 30 grams of carbohydrates beforehand helps stabilize blood sugar, which women's bodies burn through quickly. After cardio, 30 to 35 grams of protein is needed, or 40 grams for women in perimenopause or early menopause. This matters because as women age, their bodies become more resistant to the muscle-building effects of both exercise and protein—a phenomenon that doesn't occur in men to the same degree.
The fitness trends that dominate popular culture—intermittent fasting, Zone 2 training, and other widely publicized approaches—were largely developed and tested on men. They may work well for male bodies but can be counterproductive or even harmful for women. Yet most people don't pause to ask what population a trend was studied on, or whether it applies to them. Sims's work is an attempt to change that conversation, to make women ask not just what works, but what works for women specifically. In 2024, as President Biden signed an executive order aimed at improving women's health research across federal agencies, that question has finally begun to receive the attention it deserves.
Notable Quotes
Women are not small men. If we work with our physiology knowing that women are women and men are men, imagine the health outcomes.— Dr. Stacy Sims, exercise physiologist and nutrition scientist
Most of the trends out there are great for men, but it's a different story for women. The question is: what was the population it was studied on?— Dr. Stacy Sims
The Hearth Conversation Another angle on the story
Why has it taken so long for medicine to realize that women aren't just smaller versions of men?
Because the people who built science were men, and they didn't question their own assumptions. They thought they were being universal when they were actually being narrow. Tradition is hard to break.
But surely by now, with all our modern research tools, we would have caught up?
You'd think so. But even after the NIH required sex-based analysis in 2016, most studies still didn't actually separate their data by sex. The policy existed, but the follow-through didn't.
What changed people's minds?
COVID did something unexpected. When the virus hit men harder but women had worse vaccine reactions and longer-lasting cognitive effects, researchers couldn't ignore the differences anymore. Suddenly sex-specific research became good science instead of an afterthought.
So if a woman reads about Zone 2 training or intermittent fasting, should she assume it doesn't apply to her?
Not necessarily. But she should ask: was this studied on women? If it was studied on men, it might not be appropriate for her body. That's the question most people never pause to ask.
What's the single biggest mistake women make with exercise?
Doing too much steady cardio and not enough strength training. Women's bodies are already built for endurance. What they need is the metabolic and brain protection that comes from resistance work and high-intensity intervals.
And nutrition?
Eating too little protein. The recommended amount is based on old men, not on women's actual needs—especially as they age and their bodies become more resistant to building muscle.