What I Learned From Tracking My Calorie Burn for a Year

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It has been over a year since I started using MacroFactor, an app that calculates my TDEE (total daily energy expenditure) in real time. It’s a paid app, but as we noted when it came out, there are free tools that handle the same calculations. And whatever the method you use to track your TDEE, the results can be enlightening. I certainly thought so.

What is TDEE?

Before I get into what I learned, here’s a quick refresher on TDEE. As the name states, it is an accounting of your total daily energy expenditure, or calorie burn. That includes calories you burn through exercise, calories you burn by walking around and fidgeting, and calories your body burns just to keep the lights on, so to speak—firing the neurons in your brain, pumping your blood, all that good stuff.

People will often estimate their TDEE using a formula like this one, from tdeecalculator.net. When I plug in my height, weight, age, sex, and activity level into that site, I get an estimate of 2,090 calories per day. Spoiler alert: All people are different, and that rough estimate is nowhere near the number I get when I use a more accurate method.

Some people try to get a better sense of their TDEE by plugging in their numbers as if they do no structured exercise, and then adding in the calorie burn their fitness tracker reports for their exercises sessions. So let’s say the calculator thinks you burn 1,700 calories just by existing, and then you run five miles, and log another 500 burned. That would be 2,200 for the day. But exercise doesn’t burn as many calories as you’d think, so your numbers will likely be off.

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Why does your TDEE matter?

If you eat more than your TDEE, you’ll gain weight. If you eat less than your TDEE, you’ll lose weight. That’s the whole idea behind the concept of a calorie deficit or surplus. (If you eat the same amount as your TDEE, your weight should stay the same.) There are plenty of caveats to this process, but it’s the model we’re working with.

The MacroFactor app, and the spreadsheets that predate it, ask you to track your calorie intake and your weight. So I’ll have some enchiladas, and log them in the app (480 calories). Later I’ll have a banana (105 calories), and so on. By the end of the day, I’ll have a total for how many calories I ate.

Meanwhile, I’m also weighing myself every day, or at least most days. The app or the spreadsheet simply relates the two. If I’m losing about a pound a week, I’m probably burning about 500 calories per day more than I eat. That means if I’m eating 2,000 calories on average, my TDEE must be 2,500. If my weight is staying steady, then the amount I’m eating must be equal to my TDEE.

TDEE calculations are based on a model

People often recite “calories in, calories out” as if it is as reliable as the laws of thermodynamics. But it doesn’t really work that way. The numbers we have available to us are labeled calories from food packages and databases, and we can only estimate our calorie burn from any of a variety of sources. Energy can be neither created nor destroyed in the universe, true, but the way we measure food and exercise do not represent a strict accounting of energy in the physics sense. (As two biochemists once snarked, expecting different metabolic processes to yield identical energy outputs would be the real violation of thermodynamics.)

For example: how many calories your body can actually extract from food varies depending on the type of food and on factors like gut microbes that vary from person to person, and potentially even from day to day in the same person. Our food labels can’t precisely reflect all of that.

Similarly, the number of calories we get from a given food is also a rough estimate. If I eat a banana, I’ll log it as the same food item every day (“banana, medium, 7″ to 7-7/8″ long”) and thus get the same 105 calories in my food log every day. But some of those bananas will be smaller or larger than others, and they’ll release more sugars as they ripen. They’re not all going to be exactly 105 calories.

There are likewise plenty of uncertainties when it comes to calorie burn. You become more efficient at running (burning fewer calories per mile at the same pace) as you get better at running. Even if you’re gauging calorie burn via TDEE based on your weight, there are other things that can change your weight besides whether you’re burning or putting on fat. If you have a salty meal, your weight will be up the next morning. If you drink a few beers, you may be a bit dehydrated and see the scale go down. This could change your calculated TDEE, but it doesn’t change how many calories your body is actually burning.

The idea that our imprecise measure of “calories in” mathematically balances our imprecise measure of “calories out” is hardly a fundamental truth of the universe; it is a model that we simply declare to be true, and then we crunch the numbers and see what we can learn using those assumptions. Or, as the scientists like to put it: All models are wrong. Some models are useful. And this one has been pretty useful for me.

My actual TDEE is pretty different from the calculators

Let’s go back to that estimate I mentioned from tdeecalculator.net. It thinks I probably burn 2,090 calories per day. Well, according to MacroFactor, my expenditure has varied from 2,383 (when I started using it), to 2,179 (when I had COVID and skipped all my workouts for a week), to 2,516 (a few days ago).

Even given the caveats above, this information is helpful. I know that if I want to gain weight to allow for muscle growth, I need to eat foods that total more than 2,516 calories for an average day. (Thankfully, the app does the math for me, recommending a specific calorie target based on my current TDEE and the rate of weight gain or loss I’m looking to achieve.)

Exercise doesn’t increase TDEE as much as you might think

Has my exercise changed during the time I’ve been keeping records? Yes, but not always in the direction my TDEE would indicate. Last winter I rode my exercise bike almost every day and did shorter strength workouts in between my heavy days. Lately I’ve just been doing the heavy workouts and going for a daily morning walk. My TDEE is a good 100-200 calories higher now than it was when I had that Peloton app streak going.

That isn’t surprising when you consider something we know about metabolism: exercise can increase your calories temporarily, but your body tends to adapt so that you save energy elsewhere when you’re spending a lot on exercise. An active person may still have a higher TDEE than a less active person, but not by nearly as much as you’d expect.

This is also why it doesn’t make sense to track the calories you burn in each workout. I don’t track most of my workouts, so sadly I can’t go back and compare the estimates. But I feel more confident than ever in saying that the number on your fitness watch does not represent the number of calories you actually added to your total burn that day.

Eating more increases TDEE

If my calorie burn doesn’t increase much with increased exercise, what does cause those spikes and valleys across the graph? The most noticeable difference is simply how much I’m eating.

It might seem counterintuitive, but the more I eat, the higher my burn goes. This might be because my body has more fuel available, so it’s spending more on activities and metabolic processes that might otherwise be out-of-budget. On the flip side, when I’m eating in a deficit, it might be budgeting a bit more tightly.

But that’s not the only possible explanation. Remember, the TDEE model assumes that your TDEE is a single number, which it deduces from your intake and your weight change. I’ve always preferred to think of maintenance as a range. For me that might be something like 2,350 to 2,550 calories. If I wanted to lose weight, I’d have to get my calories below the bottom of that range, and the app would crunch the numbers and report 2,350 as my “true” TDEE. If I wanted to gain weight, I’d have to go above the top of that range, and the larger number would appear to be my true TDEE.

This is all sort of a gut-feeling-hypothesis, but it fits with my observations: Whatever the explanation, I can “increase” my TDEE by a couple hundred calories simply by switching from a weight loss diet to a bulking diet.

Muscle mass increases TDEE

This one is harder to track from month to month, since muscle growth is fairly slow, but if I look back further than the past year, I can tell there’s been a big jump in how many calories my body uses at a similar activity level. I used to lose weight on 1,800 calories per day, and I was able to gain weight in the low to mid-2000’s. Last year, before I started using MacroFactor, I was gaining weight on roughly 2,700 to 2,800 calories per day.

Now, my maintenance burn is 2,500. If I want to lose weight, I only need to go down to about 2,100 calories per day. To gain, I need to eat close to 3,000.

Why? Well, we know that lean body mass (including, but not limited to, muscle) affects our metabolism. You can read more about that here. Briefly, the bigger you are, and the more non-fat tissue you have, the higher your metabolism. Age, surprisingly, doesn’t factor into it much at all once you account for those two factors.

If I look back to the workouts I was doing years ago, when my TDEE was in the low 2000s, I was a smaller person—maybe 15 pounds lighter—with a lot less muscle. I’m not saying all of the difference is muscle, but probably a lot of it is. And since I wasn’t as strong, I was handling lighter weights. My working weight for a set of squats is probably 50 pounds more now than it was then; that’s going to add up when it comes to my total calorie burn.

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