Show 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 you probably aren’t average, and your needs will change over time!! In this post I’m going to show you a superior way to think about energy needs and what this means for losing weight. Here’s what we’ll cover:
Let’s begin 😉
 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 a group of 382 real women aged 20-70. Our data comes from Institute of Medicine’s Dietary Reference Intakes. Here’s a few things the data shows us:
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. Of course you never assume want to assume you’re average. I’ll explain why as we go. Calories Burned Per Day By MenMen 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.
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. Again, never assume you’re average! Let’s dig into four reason why our energy needs differ. Young people burn more caloriesAs 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 caloriesTall 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 caloriesHeavier 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 caloriesThe 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 . . ). Calorie Targets for Losing WeightThe last four graphs earlier in this article should hopefully have given you a vague idea of what your own energy might be, even if its just a broad range. To set up a solid calorie target for fat loss you need to apply a deficit to your needs. The deficit is the energy shortfall you need to create in order to lose fat. Because I have no idea where you sit on those bell curves I’m going to use this data to set a deficit for the whole distribution. For someone who is tracking all their food a 10-20% deficit is fine. But because most of our readers are regular people, rather than physique athletes, let’s go for a more aggressive 25% deficit. This should bring the create a 500-1,000 deficit for the vast majority of our sample. This is in line with the National Institutes of Health (NIH) guidelines and big enough to allow some inevitable slip ups. Weight loss targets for womenHere’s what our female distribution looks like after the 25% deficit has been applied. Here’s what we can see.
The average needs women fall into a 1,500-2,100 calorie target range. Women with low energy needs will be forced to eat 1,200-1,500 to shift fat adequately. While high burners can lose well at +2,100. I’ve shaded all the figures below 1,400 calories in orange because because these targets deserve some caution. In this sample 1,400 calorie figure does not meet the resting metabolism needs of 40% of this sample. Although it is well above the NIH safety floor of 1,200 calories for women. Note: You should think of these numbers as sensible starting targets. Our energy needs will decline as we lose weight and we are often forced to cut calories lower that we might hope. Calorie targets for menHere’s our male distribution after the 25% deficit has been applied. Here’s what we can see for men:
The bulk of our men fall into a 2,000-2,700 calorie range. The lucky guys with high energy needs can cut on +2,700 while those will low needs will need to jump straight at 2,000 or below. I’ve shaded all the figures below 1,800 calories in orange because this figure doesn’t meet the resting metabolic needs of 43% of this sample. Although once again this is well above the NIH safety floor of 1,500 calories for men. Note: Once again, please realise these figures are only designed to give you an idea of where to start. Energy needs can easily drop by 500 calories per day over the course of a cut. How we adapt to weight lossIf you’ve ever tried to lose weight, or coached people to lose weight, you’ll likely have been surprised by how high some of these numbers were. To be honest that was my reaction when I first extracted the data from the report. I spent a lot of time trying to validate how representative this sample is, and found it remarkably solid. In fact the average man and woman in the sample is roughly ten pounds lighter that the average American today. Here are the sample means.
So what’s going on with these seemingly high figures then? I’ve got two explanations for you. The first thing worth remembering is that we are universally terrible at counting calories (myself included). Even when trained dietitians where tested they we found to under-report by 220 kcal a day. So unless you are weight every gram of macronutrient you are eating don’t assume you’re are even close to knowing what your numbers are. Secondly, and perhaps more importantly, your body will adapt. During a diet your body actively defends its fat mass by reducing energy use and increasing hunger signals. This is your hormonal defence system telling your brain (the hypothalamus primarily) to protect itself from losing too much weight. Let me give you a concrete example. The graph below comes from a great free living study that looked at how people adapt to caloric restriction. Here’s what the average adaptation of people that started on a 25% deficit looked like after three months in that study. Note: These people lost an average of 6kg (13lbs) 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). So in the process of losing just 6kg the average drop in calories burned was a whopping 450 calories a day!! That’s a 17% drop in their daily total daily energy expenditure. Most of Us Underestimate How Much We EatLastly, it’s important to recognise that when someone tracks their food, it is likely that they are underestimating their energy needs by a considerable amount. This was tested in a UK population recently and the average error was underestimating intake by 32%. With women estimating intake at 1,570 calories the actual amount consumed was estimated to be 2,393. And meanwhile men tracked eating 2.065 but were in fact eating 3,119 (see below). When working with clients it is very hard to know how accurate they might be. Wrapping upHere’s what we’ve learned from this data.
Hope you enjoyed that!! |
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