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  • Ari Winfield

There's no equal playing field when it comes to biological gender and fitness...

Before I get slated for stating women and men aren’t equal - hear me out a second.

There are so many different biological factors between the sexes that come into play when it comes to diet, exercise and performance.

These factors heavily affect appetite, body composition, hypertrophy (muscle growth), metabolism and fat loss, strength and power, recovery and energy. To name some of the main ones.

And it’s women that generally have the worse hand.

I really think that both men and women (and especially PTs) need to know more about these factors and how they can affect the sexes, so I'm going to go into some of these below.

Body composition and metabolism

Just by existing, men burn more calories than women.

This is partly due to men (in most cases) being physically larger beings; they require more energy to carry that mass around and keep it functioning.

Men also (in most cases) hold more muscle than most women, and do you know what muscle does? Muscle increases your metabolism and helps to burn more energy throughout the day. Muscle requires more energy to maintain than fat tissue.

So, #1 big biological difference: men burn more calories than women.

Something James Smith PT said on social media recently really hits this home, I’ll paraphrase but here’s his example to explain the effects:

“Imagine a man and woman go to a restaurant to eat a meal. They order the same thing. It takes the woman longer to burn off the meal than the man. On average it takes a woman about 30% longer to achieve this.”
“Now imagine that same man and woman go to the gym for an hour. The man will burn more calories in his hour than the woman. To burn the same amount of calories as the man, the woman will have to work out for an hour and a half.”

Body fat percentage

This leads me nicely to #2 big biological difference: men have a lower body fat percentage than women.

Women are supposed to hold more fat than men. They need to have a higher body fat percentage to survive pregnancy: fat reserves are an essential feature from an evolutionary standpoint.

Your body needs an estimated 50,000 calories just to survive pregnancy.

It makes sense that, if a woman doesn’t eat enough, she loses her period – it’s her body’s defence mechanism to protect itself.

On average, women have 6-11% more body fat then men.

And because we have a higher body fat %, we’re more prone to female-associated features like cellulite. Which is totally normal by the way, and I have it, too. We’re also less likely – and it’s more difficult for us - to have visible abs (everyone has abs, but you’re not always able to see them beneath fat tissue).

Hormones and diet / performance

Again, this leads me nicely to the third big biological factor I wanted to talk about, and probably the one that has the biggest physiological impact. #3 - I’m talking about hormones.

The sexual glands in males and females release different hormones that bring about the physical changes of puberty. We know this, right? You should have learned this at school.

For men, there are androgens (male sex hormones) with testosterone being the most important of these.

For women, the main sex hormones are oestrogen and progesterone. But it’s important to note that women also produce small amounts of testosterone, too.

Males produce up to 10x more testosterone than females. (2017. Active IQ Level 3 Certificate in Personal Training. P50.)

So, how do these hormones affect us differently?

Again, there’s the pregnancy thing. Studies show oestrogen reduces a woman's ability to burn energy after eating, resulting in more fat being stored around the body.

There’s also the fact that testosterone is responsible for a greater muscle mass (and therefore higher metabolism), so men are more likely to have a lower body fat percentage. We’ve kind of been over this already.

But here’s one we haven’t covered yet – the menstrual cycle.

So there are four weeks in a typical 28-day menstrual cycle, during which time the hormones in a woman’s body are constantly fluctuating and ‘changing your brain’s energy levels and functionality’.

Follicular phase (days 1 – 14):

Week 1: The week of your period. Surprisingly, it’s probably the most stable your hormones are going to be for the rest of the month! ‘During this phase, the levels of all hormones are low. There’s a slight rise in oestrogen and a slight dip in progesterone. Your energy, focus, and productivity levels are at their lowest during menstruation.’

Week 2: ‘This phase sees a sharp rise in progesterone and oestrogen. Testosterone stays at a steady level, but it may rise toward the end of this phase. You have heightened energy during this phase thanks to rising oestrogen levels. It’s a good time to learn and drive to succeed may be higher.’

Mid-point (typically day 14): Ovulation – this is when you release an egg. It’s when your libido is likely to be highest (it makes sense from an evolutionary perspective that when you’re most fertile you’re also more in the mood!). Your testosterone spikes, and as a result, some of your best gym performances are seen during this time. ‘The hormonal peak of testosterone gives you an outward focused energy, while the oestrogen peak makes you feel energetic and proactive.’

Luteal phase (days 15 – 28):

Week 3 and 4: ‘Both oestrogen and progesterone rise (especially progesterone, which reaches its highest peak) before falling dramatically at the end of this phase.’

Progesterone is believed to affect appetite. Food cravings — specifically for carbohydrates — are associated with the luteal phase.

And in fact, during the luteal phase, metabolic rate increases, by about 300 calories a day. But as a result of increased appetite, women - on average - eat 500 a day more.

It makes sense that last two weeks of the cycle are the most difficult for women to adhere to a calorie deficit diet, making fat loss more difficult for women during this time.

And it’s not just the increased basal metabolic rate and increased appetite women have to deal with.

‘Fluctuations in oestrogen and progesterone levels can also affect neurotransmitters like serotonin.’
‘Serotonin plays a big role in mood swings and food cravings. If you’re lusting after carbs, your body may be attempting to self-medicate when serotonin levels dip during the luteal phase.’

This is especially problematic for those with eating disorders.

'Those who have genetic risks for eating disorders are more vulnerable to “emotional” or “binge” eating during their menstrual cycle, when it feels impossible to stop.'

Hormones and performance

Not only this, but because progesterone has such a calming/slowing effect on the brain, women will have less energy during the last two weeks of their cycle. They’re also more likely to experience worse coordination, have a higher chance of injuring themselves, and will see inferior performances in the gym.

Males have one pretty much constant physiology their entire lives (other than the gradual decrease in testosterone as they age). When you compare this to the constant hormonal changes experienced by women post-puberty, they really have got a good deal - to say it lightly!

To summarise…

This is a brief summary of just some of the physiological differences between men and women that have a big impact on diet, exercise and performance.

I wanted to write this as it’s been super helpful for me personally understanding my cycle and why some weeks I’m smashing the gym, and other weeks I’m smashing packs of biscuits.

It’s important that women track their cycles and understand how their hormones are going to impact their diet, exercise, mood… and to not beat themselves up when they’re having a bad week. There are reasons you feel this way!

And there are reasons why you find it more difficult to stay in shape than your boyfriend (assuming you're a straight woman, that is). He burns more calories, requires more energy - just to exist. Men are in a better position genetically to have higher muscle mass, leaner body composition, stronger and more consistent gym performances.

Give yourself a break girls! Hope this has been helpful...



P.S. For the purposes of this post, when using the terms 'man', 'woman', 'male' and 'female' - I'm talking specifically about biological sexes rather than gender.


‘Several factors determine your individual basal metabolism, including: Your body size and composition. People who are larger or have more muscle burn more calories, even at rest. Your sex. Men usually have less body fat and more muscle than do women of the same age and weight, which means men burn more calories.’

‘Males produce up to 10x more testosterone than females’. (2017. Active IQ Level 3 Certificate in Personal Training. P50.)

‘From puberty to menopause, women maintain more average body fat than men -- even when they take in fewer calories.’

‘Studies show oestrogen reduces a woman's ability to burn energy after eating, resulting in more fat being stored around the body’:

More information on male sex hormones

More information on female sex hormones:

More information on the cycle and its effects:

More information on the cycle and appetite/diet:

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