Two experts just blew up everything we thought we knew about women's bodies and exercise.

For decades, women have followed fitness and nutrition advice developed for men, only to end up frustrated when the same protocols fail to deliver expected results. According to Dr Stacy Sims, exercise physiologist and nutrition scientist, the problem isn't a lack of effort — it's fundamentally misunderstanding the female body.

"Everything from what happens in utero until we die is different for women than men," explained Dr Sims in a recent interview on The Mel Robbins Podcast.

"All the guidelines for exercise, mental health, sociocultural pressures... we experience things differently as women than men do, but that's not ever really explained."

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Dr Sims, from Stanford University, has pioneered a transformative approach to women's fitness. Her mantra — "women are not small men" — challenges the fitness industry's tendency to simply "shrink and pink" male-focused protocols rather than develop women-specific approaches based on female physiology.

The morning metabolism myth.

According to Dr Sims, one of the most pervasive fitness myths affecting women involves morning exercise routines. Many women follow the male-centric advice to exercise on an empty stomach, believing it maximises fat burning.

"If you get up and start your exercise without any food, the hypothalamus is like, 'wait a second, this is a stress to the body,'" Dr. Sims explained. "One of the first things that starts to get broken down is your muscle mass."

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Unlike men, women's brains require a fuel signal first thing in the morning to properly regulate stress hormones. Without this signal, cortisol remains elevated, triggering the body to preserve fat stores while breaking down muscle tissue — the exact opposite of desired fitness outcomes.

"For women, when we're looking at getting up and holding a fast or going training without food... we're going to continuously be breaking down the tissue that we want to keep to age well," Dr Sims cautioned.

The solution? Eat something small before morning exercise. Dr Sims recommended options like protein coffee (protein powder mixed with milk and espresso), overnight oats with Greek yoghurt, or even just a few tablespoons of yoghurt. This small change triggers the metabolism to work properly while protecting muscle mass.

The most effective way to train.

Another key difference centres around resistance training protocols. While cardio has traditionally been emphasised for women, Dr Sims revealed strength training offers particular benefits for the female body — especially as hormones change with age.

"When we talk about the science of strength training right now, we know that with age, we lose muscle really quickly, starting when we hit 30," said Dr Sims. "It's really important because it's an active tissue, so it helps maintain so many different systems in our body."

Beyond physical strength, resistance training offers profound cognitive benefits. "If we're strength training... it's creating signals to the brain to increase its ability to be really plastic," explained Dr Sims. "For women, strength training is great because we're changing our body composition. But for the long term, we want to have a good body and a good mind."

Dr Sims recommended that women in their 30s and beyond focus on heavier weights with fewer repetitions, rather than the traditional 10 to 12 rep approach commonly recommended.

"When you're doing the higher reps, it's more of what we call metabolic stress... but it's not an impetus to build lean mass or to become stronger," she notes. Instead, she advises using weights heavy enough that you can only perform six to eight quality repetitions.

Why cold plunges and saunas work differently for women.

The trending practice of cold water immersion illustrates another significant gender difference. While men may benefit from ice-cold plunges, women require a different temperature approach.

"When a woman gets into ice-cold or cold water, it invokes such a severe, strong stress response, much stronger than a male's response, that her body goes into more of a shutdown phase," explained Dr Sims. "If you were to take a woman and put her in 15 or 16 degrees Celsius, she'll end up with the same responses that a man has."

Conversely, women excel in heat exposure. "Women can tolerate heat a lot more than men," said Dr Sims, noting that sauna sessions provide numerous benefits, including improved cardiovascular health, better blood glucose control, enhanced fat metabolism, and improved exercise tolerance. Just 10 to 15 minutes twice-weekly can deliver significant health benefits.

Exercise as stress resilience.

Perhaps Dr Sims' most revolutionary perspective reframes our understanding of exercise itself. Rather than viewing it primarily as a calorie-burning activity, she presents exercise as a positive stressor that builds resilience.

"Exercise is a stress, the body is very adaptable to stress," she explained. "If we're looking at doing a longer, harder walk up a hill, after a couple of weeks of doing that, it's going to be easy because your body has adapted to that stress."

This adaptation extends beyond physical fitness to help manage all forms of stress. "We're teaching our body that flight by exercising and your body is like, this is a stress, I need to understand it, overcome it, get stronger," said Dr Sims. "If we're resilient to stress in a meeting, our immune system is also really resilient to stuff that's going around."

For women seeking both physical and mental health benefits, Dr Sims recommended a combination of strength training (three days weekly) and sprint interval training (30-second bursts of maximum effort with full recovery). This approach delivers maximum benefits in minimal time — often just 45 minutes to an hour total weekly exercise.

"I want women to feel ownership of their own body," concluded Dr Sims. "It starts with consistency and making time for yourself. It doesn't have to be a lot of time. It could be 10 minutes first thing when you get up... but something that is you and you own it."

By understanding and working with female physiology rather than against it, women can achieve better results with less effort — building stronger bodies and minds for lifelong health.

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Feature image: Getty/Dr Stacy Sims.