Has anyone ever told you that a woman burns 2,000 calories a day?
Or that a man burns 2,500 calories a day?
These two numbers are repeated so often, by so many people, that they are assumed to be true. But here’s the thing . . .
These numbers are both wrong, and simplistic. And if you plan your fitness or weight loss goals around them it can cause you a lot of heartache.
The average calories burned per day by a real American woman is actually closer to 2,400, while for a man it’s about 3,100. But even more accurate averages can easily mislead us.
In this post I’m going to show you a superior way to think about the energy needs of men and women. Rather than use some textbook definitions or formulas we are going to use real data from Institute of Medicine’s Dietary Reference Intakes. Our sample is 382 women and 264 men aged 20-70.
Let’s destroy this myth that we are all ‘average’!
Calories Burned Per Day By Women
Calories needs are like like shoe sizes.
Some people need small shoes, some need big shoes, but most people are somewhere in the middle. Shoe sizes have what we call a ‘normal’ distribution. This is a bell curve shape.
The energy needs of women have a very similar distribution (they are linked by height). Here’s how calories burned per day are distributed among our group of 382 women.
Here’s a few things the data shows us:
- 20% of these women burn less than 2,000 calories a day (low needs)
- 65% need between 2,000 and 2,800 calories (average needs)
- 16% these women burn more than 2,800 calories a day (high needs)
- the median woman in this sample burns 2,365 calories
There isn’t a single women among this group that needs exactly 2,000 calories a day. In fact the average calories burned per day by a woman in this sample is closer to 2,400 calories.
But never assume you’re average!
Calories Burned Per Day By Men
Men are lucky!
They have have more muscle, less fat and larger organs (liver, kidneys, heart) at similar bodyweight which means they have higher metabolic rates.
Here’s what the distribution of our 264 men looks like.
And these are the quick takeaways from our males.
- 19% burn less than 2,600 calories a day (low needs)
- 59% need between 2,600 and 3,600 calories (average needs)
- 20% burn more than 3,600 calories a day (high needs)
- the median man burns 3,076 calories
Once again there isn’t a single man in this sample that needs exactly 2,500 calories a day. In fact the average calories burned per day by men in this sample is closer to 3,100 calories.
But again never assume you’re average!
Update: I had a number of colorful emails asking to explain the data.
First, here are the sample means:
- Women: 43 years, 69kg (153lbs), 164cm (5’5), PAL: 1.74
- Men: 43 years, 83kg (183lbs), 178cm (5’10), PAL: 1.77
Now although there are genetic factors which are hard to pin down I can shed a little light on four key drivers: age, height, weight and activity level.
Let’s look at each in more detail:
Young people burn more calories
As people get older their energy needs tend to decline. Explaining this phenomenon is not straight forward. Some of it is lost muscle mass, some changing lifestyle and some seems to be things changing at a cellular level too.
Whatever the reason is you can see it clearly in the data.
The first thing to note is the enormous variation. The second is the clear decline in energy needs with age. Average needs for women drop from 2,700 calories at age 20 down towards 2,000 at age 70. While for men they begin way up near 3,400 at 20 and fall to 2,800 by 70 (which seems surprisingly high).
Tall people burn more calories
Tall people generally burn more energy than shorter people, so they can afford to eat more while maintaining weight and have more energy to play with when cutting. Part of this is simply having more surface area to dissipate heat. Here’s how the data looks.
Virtually all the women with slower metabolisms (below 2,000) are shorter than 170cm (5’7). In the black dots for men you can see that the bulk of the high energy users (above 4,000) are up around the six foot mark.
Heavy people burn more calories
Heavier people generally have higher metabolic rates. This reflects the fact that more energy is required to move a larger body and that larger people often have bigger muscles and organs (resulting in higher resting metabolisms). Here’s how the data looks for weight:
In this graph you can see that even for the same weight men typically have an energy expenditure that is 500 calories higher than women. Light women who clock in around 50kg (110lbs) average just 2,200 whereas a 100kg (220lbs) woman could expect to use 2,800.
The effect of weight on energy needs is even greater in men. With 100kg (220lbs) men regularly clocking in around 3,500 calories a day it’s little wonder big men often drop weight the fastest. It’s again important to stress the huge variation.
Active people burn more calories
The primary reason you should be careful with a TDEE calculator, or any weight loss calculator for that matter, has to do with their treatment of activity level. Almost all calculators estimate your resting metabolism (which already has a degree of variability ±20%), and then multiply it by an activity multiplier based on exercise levels (typically 1.2, 1.375, 1.55, 1.725, 1.9). But getting these multipliers right is very hard. And pretending they are determined largely by exercise is plain false. They are a complex function of genetics, work life, exercise patterns, muscle mass, postural control, propensity to fidget . . .
Here’s what the correlation looks like between TDEE and activity level.
Activity level is a stronger explainer of TDEE than age, weight or height. In this data set it explains 40-50% of the variation.
If you’ve ever known one of those people that just doesn’t seem to put weight on regardless of what they eat you’ll probably find they are a world class fidgeter. Other things that drive up activity levels are physically active jobs (think labourer) and endurance training (think triathlete). People with low activity levels (below 1.5) are likely to combine desk jobs, limited exercise and low spontaneous activity (fidgeting, posture control, shivering . . ).
Let’s wrap this up!
Don’t be too simple
Einstein is understood to have once said:
Everything Should Be Made as Simple as Possible, But Not Simpler
Assuming your energy needs are average, or static for that matter, is a simplification too far. Your energy needs could be very different from the average and they will decline if you lose weight, or increase if you bulk up.
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