Imagine if you walked into a shoe store, asked to try on a pair of sneakers and were told they only have one size. For all of their shoes!!
I’m talking about a store that only stocks a Size 7.
It’s a silly idea right? We all know people need different size shoes.
So tell me this?
Why on earth do government and fitness websites across the globe persist with the idea that ‘a woman burns 2,000 calories a day’? Then proceed to dispense advice designed for this mythical 2,000 calorie a day woman?
The idea that ‘women burn 2,000 calories a day’ is a simplistic fallacy. Female energy needs have a broad bell shaped distribution and can change over time in response to diet and activity. Telling women they ‘burn 2,000 calories a day’ sets many women up for failure even before they start.
In this post I’m going show you why its a myth that women ‘need 2,000 calories a day’, then give you a good sense of what type of calorie intake is required for a woman to lose weight.
Let’s begin 😉
A Bell Curve of Female Energy Needs
I used the metaphor of shoe sizes for good reason.
Female shoe sizes have a largely normal distribution. That is to say the’re spread out in a bell curve fashion around Size 7 in the middle. This curve looks a lot like the distribution of female energy needs (its connected by height).
To illustrate this I’ve grabbed some data from the Institute of Medicine’s Dietary Reference Intakes. Here’s a histogram showing how energy needs are distributed among 382 women aged 20-70.
A few things stick out about these women.
- 20% burn less than 2,000 calories a day
- 65% need between 2,000 and 2,800 calories
- 16% need more than 2,800 calories a day
- the median woman burns 2,365 calories
That’s right. The woman in the middle needs 2,365 calories a day! In fact not a single women burns exactly 2,000 a day.
Bottom line: Women’s energy needs have a bell shaped distribution
The Problem With “2000 Calories A Day”
Treating all women like a homogeneous group of 2000 calorie burners often results in women setting a wildly inappropriate calorie target for their goals. It can also promote inflexibility by leading people to think their needs stay stable (they aren’t).
Let me give you an example.
The National Health Service in the UK dispenses the following advice to help people achieve healthy weight loss of 0.5kg to 1kg (1lb to 2lb) each week.
For most men, this means sticking to a calorie limit of no more than 1,900 a day, and 1,400 for most women.
These figures have their origin in data suggesting that the typical British female ‘needs 2000 calories a day’ to maintain a healthy weight, while for a male ‘the figure is 2500’. From this they simply subtract 600 kcal a day, which is the size of NICE’s deficit guideline for sustainable fat loss.
Now subtracting 600 kcal a day from your true calorie needs is a solid way to set calories. And if all women did need 2,000 calories a day then a 1,400 target would be solid. But let’s take a look a what type of deficit eating 1,400 calories creates for the 382 women in our data set.
Ok, I admit this chart looks a little daunting. But this is important!!! Stick with me 😉
Let’s group our women together. From left to right on the chart.
- In a surplus (3 women): The three women eating a surplus are all 60 years plus and can actually gain weight on just 1,400 calories!
- 0-500 deficit (51 women): They will see slow weight loss which might be hard to perceive on a scale due to water weight fluctuations.
- 500-1,000 deficit (146 women): These women are probably the sweet spot to begin with! The 500-1,000 deficit will result in steady losses without stressing hormonal defences too much.
- 1,000-1,500 deficit (130 women): These are pushing it dangerously hard, over the often cited limit of 1,000.
- +1,500 deficit (52 women): This is pure masochism!
Now remember the goal of this 1,400 calorie diet was create a 600 calorie deficit, but in reality it ranges from a surplus of 150 calories to a deficit of more than 2,200 calories.
Sure 1,400 calories might be perfect for a 60 year old women that is a desk bound executive. But for her 28 year old sport loving daughter that spends her day on her feet as a teacher 1,400 could be a crash diet.
Bottom line: One size fits all calorie targets are not scientific
Setting Smart Calorie Targets
OK, so its pretty clear the one size fits all targets is not fit for purpose. What should you do instead?
The world experts in fat loss (natural bodybuilders) track their calorie needs before dieting work out their ‘maintenance’. Then they cut 15-25% from this to get things moving. This creates a personalised target which is adjusted down further as the diet progresses.
This is an invaluable process if you can be bothered. And its something I wish I’d done for just two weeks before starting out. But at the same time doing this properly means weighing every gram of food. You can’t just throw a ‘tablespoon of peanut butter’ into MyFitnessPal and pretend like you know what your macros are.
If weighing all your food sounds too obsessive (that’s why I don’t do it) then a great alternative is to aim for a target rate of weight loss (0.5-1% of bodyweight a week). With this approach you just focus on eating a consistent diet and then adjust calories up or down based on results. Ideally you won’t even need to track calories to do this either. It’s much more about focusing on consistency and then making adjustments.
Now at this point I realise lot of people will be asking ‘what is a good calorie target for me?‘ So let’s try to come up with something smart.
To kick things off I think a 25% deficit is aggressive but practical. I say this because your average dieter needs to see results early on and benefit from some wiggle room for a few misses. Also by using percentages we allow women with higher energy needs to cut harder, because hey can afford it!
So lets see what our distribution looks like with a 25% deficit applied to it.
Ok, here’s what we can see.
- low energy needs: target range 1,200-1,500 calories
- average energy needs: target range 1,500-2,100 calories
- high energy needs: lose weight at +2,100 calories
I think this graph gives a great ballpark idea of how many calories women need. I’ve shaded all the figures below 1,400 calories in orange because such low targets should be approached cautiously. Particularly by younger women.
Bottom line: Fixed calorie targets aren’t smart
Start high then finish low
The first problem with the idea that women need ‘2000 calories a day’ is that this it’s a wildly inaccurate generalisation. The second problem is that it reinforces the idea that your energy needs are static.
This is not the case.
Your body is will actively defend its fat mass. If you have recently lost 20lbs it’s a solid bet that your energy needs will now be 300-500 calories a day lower than when you began. You’ll also likely be hungrier.
This is your bodies hormonal defence system telling your brain (the hypothalamus primarily) to protect itself from losing too much weight by reducing energy use and increasing hunger and food awareness.
Let me give you an concrete example.
The graph below comes from a great free living study that looked how people adapt to caloric restriction. Here’s what the average adaptation of people on a 25% deficit looked like after three months in that study.
These people lost 6kg (12lbs) in 3 months. At the start of the diet the deficit averaged 712 calories but by the end it had dwindled to just 258. The downward adaption was largely due to the decline in spontaneous activity (NEAT).
This type of adaptions is why bodybuilders keep adjusting their calories down as their preparation continues. They need to outsmart their body and there is only so much time in the day to add calories with cardio.
What does this mean for a ‘normal woman’?
A typical woman (in the middle of the distribution) will do really well starting her diet at 1,800 calories to begin with. But as time goes by she will need to cut calories further to progress. If she’s patient should could spend a month at 1,800, then 1,700, 1,600 and 1,500.
Without making these adjustments reaching her goal weight could take years instead of months. And by starting high and then moving lower as time goes she’ll be much more skillful when she has to go digging at 1,500.
So that’s they take away.
Bottom line: Start as high. Be patient. Finish low
Wrapping this up
OK, so what did we learn?
- Female energy needs are a bell curve centred around 2,400
- Fixed weight loss targets like 1,400 are not fit for purpose
- 1,500-2,000 is good range for most women to start losing weight
- You may well end up going lower that 1,500 to keep things moving
That was an lot of science!! I you made it this far, it was a pleasure 😉
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