It’s been over a year since I started using MacroFactor, an app that calculates my TDEE (Total Daily Energy Expenditure) in real time. It is a paid application, but as we noted when it came out, there are free tools that handle the same calculations. And whatever method you use to track your TDEE, the results can be illuminating. I certainly thought so.
What is TDEE?
Before I get into what I learned, here’s a quick refresher on TDEE. As its name indicates, it is an accounting of your total daily energy expenditure or calorie burn. That includes the calories you burn through exercise, the calories you burn walking and fidgeting, and the calories your body burns just to keep the lights on, so to speak, firing the neurons in your brain, pumping your blood, all those good things.
People will often estimate their TDEE using a formula like this, from tdeecalculator.net. When I plug my height, weight, age, gender, and activity level into that site, I get an estimate of 2,090 calories per day. Spoiler alert: everyone is different, and that rough estimate is nowhere near the number I get when I use a more precise method.
Some people try to get a better idea of their TDEE by entering their numbers as if they weren’t doing structured exercise, and then adding calorie burn to their fitness tracker reports for their workouts. 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 thinkso your numbers are probably wrong.
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 many caveats in this process, but it is the model we are working with.
The MacroFactor app and the spreadsheets above ask you to track your calorie intake and weight. So I’ll eat some enchiladas and log them on the app (480 calories). Then I eat a banana (105 calories), and so on. At the end of the day, I will have a total of how many calories I ate.
In the meantime, I also weigh myself every day, or at least most days. The app or spreadsheet simply relates the two. If I’m losing about a pound a week, I’m probably burning about 500 calories a day more than I eat. That means if I’m eating 2,000 calories on average, my TDEE should be 2,500. If my weight stays stable, then the amount I’m eating should equal my TDEE.
TDEE calculations are based on a model
People often recite “calories in, calories out” as if it were as trustworthy as the laws of thermodynamics. But it doesn’t really work that way. The numbers we have available to us are labelled calories from food packages and databases, and we can only estimate our calorie burn from any of a variety of sources. Energy can’t be created or destroyed in the universe, it’s true, but the way we measure food and exercise doesn’t represent strict energy accounting in the physics sense. (What two biochemists once gruntedexpecting different metabolic processes to produce identical energy outputs would be the real violation of thermodynamics.)
For example: The amount of calories your body can actually extract from food varies depending on the type of food and 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 accurately 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 will record it as the same food every day (“banana, medium, 7″ to 7-7/8″ long”) and therefore get the same 105 calories on my food log every day. But some of those bananas will be smaller or larger than others, releasing more sugars as they ripen. Not everyone will be exactly 105 calories.
There are also many doubts when it comes to burning calories. You become more efficient at running (burn fewer calories per mile at the same pace) as you get better at running. Even if you’re measuring calorie burn via TDEE based on your weight, there are other things that can change your weight besides whether you’re burning or gaining weight. If you have a salty meal, your weight will increase the next morning. If you drink a few beers, you may be a little dehydrated and see the scale go down. This might 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 simply to declare to be true, and then we crunch the numbers and see what we can learn using those assumptions. Or, as scientists like to say: All models are wrong. Some models are useful.. And this one has been quite useful to me.
My actual TDEE is quite different from the calculators
Let’s go back to that estimate I mentioned from tdeecalculator.net. He thinks I probably burn 2,090 calories a day. Well, according to MacroFactor, my spending has ranged from 2,383 (when I started using it), to 2,179 (when I had COVID and skipped all workouts for a week), to 2,516 (a few days ago).
Even considering the caveats above, this information is useful. I know that if I want to gain weight to allow for muscle growth, I need to eat foods that add up to more than 2,516 calories on an average day. (Thankfully, the app does the math for me, recommending a specific calorie goal based on my current TDEE and the rate of weight gain or loss I’m looking to achieve.)
Exercise doesn’t raise TDEE as much as you 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 stationary bike almost every day and did shorter strength workouts in between my heavy days. Lately I’ve only been doing heavy exercises and going for a walk every day in the morning. My TDEE is 100-200 calories higher now than it was when I had the Peloton app streak.
That’s not surprising when you consider something we know about metabolism: Exercise can temporarily increase your calories, 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 as much as one might expect.
This is also why there is no point in keeping track of the calories you burn each workout. I don’t track most of my workouts, so unfortunately I can’t go back and compare estimates. But I feel safer than ever in saying that the number on your fitness watch does not represent how many calories you actually added to your total burn that day.
Eating more increases TDEE
If my calorie burn doesn’t increase much with more exercise, what does it causes those peaks and valleys across the graph? The most noticeable difference is simply how much I am eating.
It may seem counterintuitive, but the more I eat, the bigger my burn. This could be because my body has more fuel available, so it is spending more on activities and metabolic processes that would otherwise be out of budget. On the other hand, when I’m eating on a deficit, I might be budgeting a little tighter.
But that is not the only possible explanation. Remember, the TDEE model assumes that your TDEE is a single number, derived from your intake and weight change. I have always preferred to think of maintenance as a range. For me that might be something like 2350 to 2550 calories. If I wanted to lose weight, I’d have to cut my calories below the lower end of that range, and the app would process the numbers and report 2350 as my “true” TDEE. If I wanted to gain weight, I would have to go above the upper limit of that range, and the higher number would appear to be my true TDEE.
This is kind of an intuitive hypothesis, but it fits with my observations: whatever the explanation, I can “increase” my TDEE by a couple of hundred calories just by switching from a weight loss diet to a bulking diet. diet.
Muscle mass increases TDEE
This one is harder to track from month to month as muscle growth is quite slow, but if I look further back than last year I can say there has been a huge jump in the number of calories my body uses in a similar level of activity. I used to lose weight on 1,800 calories a day, and was able to gain weight in the 2,000s to 2,000s. Last year, before I started using MacroFactor, I was gaining weight on about 2,700 to 2,800 calories a day.
Now, my maintenance intake is 2,500. If I want to lose weight, I only need to get down to about 2,100 calories a day. To win, I need to eat about 3,000.
Why? Well, we know that lean body mass (including but not limited to muscle) affects our metabolism. You can read more about it here. Simply put, the bigger you are and the more non-fat tissue you have, the higher your metabolism will be. Age, surprisingly, doesn’t count for much once those two factors are taken into account.
If I look back at the workouts I was doing years ago, when my TDEE was in the 2000s, I was a smaller person, maybe 15lbs lighter, with a lot less muscle. I’m not saying everybody of the difference is the muscle, but probably a lot of it is. And since he wasn’t as strong, he handled lighter weights. My working weight for a set of squats is probably 50 pounds heavier now than it was then; that’s going to add up when it comes to my total calorie burn.
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