Calories, Women & Endurance

At over 4,000km in length, the Pacific Crest Trail requires stamina, endurance and plenty of food to fuel the effort. But as Amy Paton moved deeper into the thru-hike, she noticed men and women responded differently to the physiological challenges. Once she got home to Oz, she decided to do some research to understand why. Here’s what she discovered.

Words + Photography: Amy Paton

Contributor’s Note

This article discusses sex-based performance differences in endurance activities. It also interrogates the interplay between sex and gender. I recognise the limitations of my experience as a cisgender female and acknowledge that this article fails to include the experiences of intersex persons, or those whose gender identity doesn’t match their assigned sex. I also recognise that sex-based performance differences exist on a spectrum, and that this piece largely speaks in generalities, while still recognising that individual counter cases exist. The outdoors community benefits from all forms of diversity and, while I’m not the right person to tell those stories, I sincerely look forward to hearing more of them.

“No way!” Matty looks mesmerised as he accepts the proffered phone, his gaze moving between the screen and the man in front of him.

I know exactly what he’s looking at, though I can’t yet see the device myself. I picture it before I’m handed the phone in a well-rehearsed ritual, imagining a shorter beard, cleaner clothes and—the object of most interest—his additional weight.

Sure enough, once the device has made its way into my hand, I’m examining a regular, perhaps slightly overweight man. He looks like your GP, or maybe the bloke at school pick-up whose name you can never remember.

I glance back at Jim, grinning at our reactions. There’s no doubt the weight loss is substantial; his arms hang gangly by his sides and his cheeks are sunken slightly where once there was ample flesh. He’s alright for now—pretty chuffed with himself if he’s being completely honest—but we’re only a little over halfway through this hike and he hasn’t got much left to lose.

The image Matty and I were looking at was taken at the Southern Terminus of the Pacific Crest Trail (PCT), a 4,265km border-to-border hike the length of the US. At the time, we were trudging our way north through the seemingly endless state of California and we’d experienced some variant of this interaction most days.

By this point on trail, I was over a month into my own anecdotal research into weight loss. In the inverted reality of thru-hiking, calorie counting is not a bygone trend of ‘90s diet culture, but a daily ritual of marrying energy output with input and almost always coming up short. If your goal is to complete the length of the PCT in one go, as ours was, it’s not long before 35km and one thousand metres of elevation is an easy day. An interplay between visas and seasonal windows means that some degree of push is required to make the distance in a season.

While town days are essential for doing laundry, contacting home, and attempting to scrub some of the permanent filth from your body, food is the main event. In which diner can you scoff down the most calories for the cheapest price? And once you’ve thoroughly alarmed the staff with your enthusiasm to devour the entire menu, it’s time to resupply. This process involves scouring the packaging of every non-perishable food from ramen to sherbet, with purchasing decisions made almost exclusively on which items have the highest calorie-to-weight ratio. Insider knowledge is passed from hiker to hiker with an air of reverence: Did you know that McDonald’s mayonnaise sachets add an extra ninety calories to any meal? Have you tried crushing potato chips into your tortilla at lunch? And are you aware that if you stand on them, you can fit a dozen bagels in your bear can?

Despite this neurotic focus on maximising energy input, once you’ve eaten, it’s up to your body to make the most efficient use of those calories, and as it turns out, not all bodies are created equal in this respect.

While many hikers, like Jim, offered up stories of their own weight loss, accompanied by photographic evidence, I’d taken to asking as many people as I could about how the trail had changed their bodies. My interest was initially piqued when comparing the effect of the trail on myself and my partner. He lost a few kilos in the first weeks alone and, as his beard began to consume more of his face, he increasingly took on the appearance of Cast Away’s Tom Hanks. By contrast, my own weight remained stable. As I continued my citizen-science interrogation, the correlation between sex and weight loss became harder to dismiss.

Now I’m not a scientist, but I’m familiar with the mantra correlation is not causation. So, armed with my anecdotal evidence, and an enthusiasm for finding new ammunition to use against the doctrine of male superiority, I set about seeing whether there was any meat to this at all. Turns out there’s a bit.

Using available energy efficiently is always the body’s goal, but over longer, slower distances, male bodies don’t always come out on top. Women have been shown to have higher fat-oxidation rates during low-to-medium-intensity exercise than men, meaning female bodies use fat favourably, which helps to preserve glycogen from carbohydrates. This matters because while the body can store near-endless calories in the form of fat, its ability to store glycogen is strictly limited. If you’ve ever ‘hit the wall’ or experienced a sudden energy crash during an endurance event, you’ve likely burned through this scant supply.

Part of the reason for this is that while men boast a higher proportion of Type II (fast-twitch) muscle fibres which are essential for bursts of power and speed, Type I (slow-twitch) muscle fibres cover a greater relative area in women’s bodies. Type I muscle fibres are known for their higher fatigue resistance, partly thanks to their ability to break down fats for energy.

So, while women’s bodies are busy making efficient use of fat for fuel during exercise, male bodies are, paradoxically, losing fat stores at a faster rate. In another masterclass in energy efficiency, women’s increased fat oxidation is reversed after exercise. In these periods of relative rest, female bodies switch to burning carbohydrates and conserving fat. The effect of this post-exercise period of reduced fat oxidation is such that, in the long term, men tend to metabolise more fat than women participating in the same activity.

Oestrogen is the bedrock of these energy systems, optimising efficiency at all but the highest intensity of activity. Oestrogen is at play, too, in recovery. Its role is complex, but a key benefit for women participating in endurance activities—particularly those spanning multiple days, weeks or months, like long-distance hiking or bikepacking—is its function in reducing inflammation.

Back on the PCT, it would still be months before I understood the physiology of why my body was responding differently to the demands of the trail than my partner’s. Nonetheless, it continued to intrigue me, and as I discussed my observations with other hikers, there was one counterargument that arose more than most: Women, it was claimed, simply have less body weight to lose. This isn’t entirely incorrect in the context of the PCT, but it’s incomplete, and the reasons for this are as varied as the individuals themselves. Nonetheless, this argument highlights a significant, and related, barrier to women getting on trail.

For many women, and especially those who might not see an ‘athletic body’ when they look in the mirror, the biggest hurdle is believing they belong in these spaces at all. Whether it’s applying for a job or beginning a thru-hike, you’re more likely to be appropriately, or even overly, prepared if you’re a woman. And it’s not all in our heads. When it comes to adventure and the outdoors, women tend to be questioned more thoroughly about their plans and experience, to be given well-meaning (if often unsolicited) advice, and to be judged categorically for their gender when they make mistakes. We’ve come a mighty long way from frowning upon female participation in the boys’ clubs of outdoor-adventure sport, but these entrenched beliefs and behaviours still narrow the pool of women who make it to the starting lineup today.

It matters that we know and discuss both the physiological disadvantages and the advantages of female bodies if we want to support women’s participation in the outdoors. When women are judged against the standards set by male adventurers, athletes and explorers during their long history of preferential access to sport and the outdoors, we may arrive at the belief that women are less suited to these pursuits. We should instead envision the outdoors as a powerful liminal space where the systemic advantages of everyday life are dulled, and challenge and possibility are more evenly distributed. While men may generally, though not always, enjoy the physiological benefits of proportionately higher muscle mass and strength, we should also recognise that women’s higher proportion of Type I muscle fibres—and their ability to oxidise fat and burn calories more efficiently—confers advantages, particularly when it comes to long-distance outdoor activities. We’re living in an exciting time when female athletes are beginning to overtake their male counterparts in ultra-endurance events, and we need to start seeing and celebrating these women for what they are: not outliers or wildcards, but the beginning. I look forward to seeing how the finish lines of these events change and evolve in the coming years, but I also look forward to taking a wrong turn on a hike and laughing it off without feeling that I’ve played right into a stereotype.

Reaching the PCT’s Northern Terminus (not a kilo lighter than I started) was a sensation of pride and potential no one should feel denied. Women do not thrive in outdoor-endurance activities despite their bodies; we thrive because of them.

About the Author

Amy Paton is a Sydney-based recovering thru-hiker. She’s begun writing about adventure as a way to leverage intrusive thoughts of quitting her day job and living permanently out of her hiking pack.

Originally published in WILD magazine, Spring 2026, pages 52–55. Words and photography by Amy Paton.