My god. If I see one more fucking fitness influencer say this, I actually think I’ll lose it.
Ok, not really.
But I’m sure you’ve heard this advice being dished out like Oprah hands out free cars. Or whatever it is she gives away. I dunno, I don’t watch Oprah––I just saw a meme once.
Anyway, where was I? Oh, right–
Here’s the thing: Some people––especially smaller women with low activity levels––will likely need to eat close to, if not below that 1200 number, to lose fat.
Not because their metabolism is ‘broken’.
Not because they’ve damaged their ‘bodies’.
But because their energy expenditure is just really that low. The fact that this is considered ‘controversial’ blows my mind.
So today, I’m going to blow your mind by explaining why blanket statements about how much someone ‘should’ eat are capital D dumb.
Let’s start here
The image below is adapted from a 2021 study where researchers analysed total daily energy expenditure (TDEE) in 6000+ people worldwide. [1]
Note that while heavier people burn more energy, there’s a lot of variation at any given body weight. See that yellow box? Some men and women are burning 1200-1400 calories per day.
We see a similar pattern when we look at the relationship between TDEE and fat-free mass (FFM)––i.e. everything in your body that isn’t body fat.
FFM has the strongest correlation with RMR of all body composition variables, so individuals with more fat-free mass will have a higher metabolic rate. Indeed, when we look at the relationship between FFM and TDEE, we can see that as FFM increases, so do daily energy requirements. But just like body weight, there’s still a surprising amount of variation at any given level of FFM.
An average 30-year-old man has around 35 kg (~78 lb) of fat-free mass, while a woman of the same age typically has about 21 kg (~46 lb). [2] Aa
If you look at the image above, you’ll see that 35 kg of fat-free mass corresponds to a TDEE range of roughly 2400 to 4000 calories per day in males. In comparison, 21 kg of fat-free mass in females could mean a TDEE as low as 1300 calories per day or as high as 2500 calories per day.
So, if someone is maintaining their weight on 1600 calories and wants to lose a pound per week, they’d need to cut about 500 calories per day — which brings them to a daily calorie target of 1100 kcal. What else are they supposed to do?
But let’s put the extremes aside and look at some real-world examples.
I calculated the TDEE for sedentary females across a range of typical body weights using the Mifflin-St. Jeor formula and the number of calories they need to eat to lose a reasonable 0.5% of their total body weight per week.
From the jump, we can see that sedentary females need around 1300 calories to lose 0.5% of their total body weight per week.
Hold on, though, because this is where it turns into fifty shades of what the fu—?
Even the most accurate calorie calculators aren’t perfect in their estimates
In one study, the best equation correctly estimated RMR within 10% of the actual measured value for about 2 out of 3 men and just over half of women. [3]
That means 30 to 40% of people had predictions that were more than 10% off — which can be a difference of 200–300 calories.
And although most people were within 10%, a small number saw errors as high as 30%.
So, assuming the best-case scenario of a 10% error, how would this impact calorie needs?
Here’s what it looks like for the 70 kg female from the previous table, showing her actual TDEE after applying the 10% error, along with the corresponding intake needed to lose 0.5% of her body weight per week.
As you can see, someone whose TDEE was overestimated would lose weight more slowly on the recommended calories, and these are the same people being told they shouldn’t drop their calories below a certain amount.
Can you see the issue? This individual might assume there’s something wrong with their metabolism or be accused of lying about their intake.
Cue the frustration. Or worse, they get so fed up that they fall for the next con artist selling a “metabolic healing plan.” Sigh.
There’s one other thing that can impact calorie requirements: Metabolic adaptation.
As you lose weight, several adaptations occur in the body to reduce your daily energy expenditure, and how much metabolic adaptation occurs can vary between individuals.
Individuals who experience more metabolic adaptation tend to lose less weight than those who don’t experience as much. [4]
In practical terms, two people could start a diet eating the same amount, but the person who experiences more metabolic adaptation would need to eat fewer calories to achieve the same amount of weight loss as the other.
Here’s an example.
In one study, young, healthy men ate in a 50% deficit for three weeks, then a 50% surplus for two. [5]
On average, their metabolic rate dropped by ~100 kcals during the deficit, but the individual response varied a lot. Some saw little change, while others experienced a steep decline.
Strawman!
You might argue that not everyone is sedentary, so I’m intentionally picking that activity level to strengthen my argument — to which I’d respond, touché.
But that only strengthens the point I’ve been making: the idea that nobody should go under a certain number of calories assumes everyone has the same energy needs. But they don’t.
Furthermore, people grossly overestimate both how active they are and how much their activity impacts TDEE. And when you’re in a calorie deficit, physical activity contributes even less to energy expenditure than when you’re eating at maintenance or in a surplus.
So yes, moving more will increase your TDEE, but the increase is often much more modest than people realise, especially during weight loss.
For example, when I did my walking experiment, I doubled my step count from ~5500 to ~11k steps per day––putting me firmly in the ‘active’ category––yet my TDEE only increased by an estimated 170 calories. [6]
And let’s not forget that any increases in expenditure via activity are further dampened when we factor in metabolic adaptation.
To bring this to life, let’s run an example — a 30-year-old woman, 5’4”, lightly active, starting her diet at 75 kg.
Her estimated TDEE is 1996 kcal/day (per the Mifflin St. Jeor formula), and she begins her fat loss phase by eating 1580 kcal/day. After losing 10% of her body weight (7.5 kg), her TDEE naturally drops—a general rule of thumb is that TDEE decreases by about 25 kcal for every kilogram lost due to reduced energy needs of a lighter body. [7]
So that brings her TDEE down to ~1800 calories/day. Next, we’ll adjust for metabolic adaptation––i.e. the additional adaptations that occur after accounting for losses in fat- and fat-free mass. Generally, metabolic adaptation can range between 5-10%, so I’m going with 7% since it’s in the middle. It was also the amount of metabolic adaptation found in a recent study after a weight loss of 11%. [8]
Her TDEE is now down to 1680 calories. If she wants to continue losing 0.5% of her total body weight/week, she needs to eat ~1300 calories. And if we factor in a 10% error margin in the original TDEE estimate, her actual calorie needs could range from ~1100 to ~1400 kcal/day (depending on whether her original TDEE was under – or overestimated).
The point?
Blanket statements about how much someone should and shouldn’t eat aren’t just unhelpful––they can be damaging to people’s progress.
Not only do they ignore individual differences, but they also make people feel like they’re doing something wrong, even when they’re not.
Worse, this messaging scares good coaches from doing what’s needed because they’re terrified they’ll get cancelled for ‘starving clients.’
But instead of having honest conversations so people can make informed choices that actually align with their goals…we’ve got Becky filming TikToks telling everyone they’ll ruin their life if they go below some arbitrary number.
Respectully, Becky, please shut the fuck up.
As for you, dear reader: I hope this article helped you understand why you might need to eat fewer calories than someone else who, on paper, seems pretty similar to you. But more importantly, I hope it showed you that if you’re one of those people who needs to dip below whatever arbitrary calorie number the Society of Collective Internet Fucknuts told you never to cross…
You’ll be fine.
You’re not going to ‘damage’ your metabolism. You’re not going to slip into starvation mode, and you certainly don’t need a shitty ‘metabolic healing plan’.
Instead, you might actually make some progress.
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