BMR/TDEE Calculation

Just want the forum to scrutinize my process here:

I have detailed records of food intake for the last 32d, as well as Kj from workouts. Also, I have lost 4.7 lbs in the process.

I created a formula in which daily BMR + KJ’s is my nutrition requirement and the aggregate deficit should be equal to 4.7 x 3500.

In my case, seems that I need to eat at least 2640 kcal daily + the KJ’s of the bike to not lose or gain weight, theoretically, based on the last 32 days.

This seems practical and data based. Can you guys poke any holes to these calculations or any potential blind spots, and explain how those issues can ruin a nutrition plan?

Current Weight 64kg
BF% ~12-15%
10-12h biking a week
FTP 270w
VO2Max = 64 mL/kg/min
Age 58

Thanks, Old

Can you lay out your assumptions more clearly?
For example, you’re assuming a defeicit of 3500 calories equals 1 lb of body weight?
So you assume your BMR is your calories eaten plus MJ burned on workouts minus 3500x4.7 lbs lost?

I think the flaw to backing out your BMR that way is the high variability of body weight and fluid retention. You’re assuming body weight loss is only from fat/muscle loss and not merely water weight, correct?

Correct. Just a convention I found on internet. This indeed can be a source of error.

Yes, you bring a good point about fluids, but I have no way to control for this.

I can only bet that in the long run the calories ins and out are what matter and the other stuff averages out to 0.

I wonder how much metabolic efficiency plays into this. 1 Cal = 4.184 kJ, so getting to the 1 Cal ≈ 1 kJ per your power meter assumes an efficiency of 23.9%. That’s on the high side for most people and can vary based on intensity.

With higher volume/more kJ’s, you could potentially be underfueling if you stick firmly to that estimate.

But then you factor in water weight, food estimates that can be within a 20% margin of error (per FDA anyway), and power meter accuracy, there’s a whole lot of fuzziness here.

At least that’s my excuse for not dropping my weight faster :thinking::rofl:

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This isn’t BMR but it would approximate TDEE less exercise from cycling.

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You are correct

Yes, the only correction is to measure its accuracy with respect of bodyweight. Wonder what @WindWarrior would say, he is the king of fuzzy measurements.

Hey Old and all…

Calorie is a calorie, but not in the nutrition/dietary context.

Dr Ben Bikman is a leader in the area and talks through how calorie counting gets messed up after food enters the body. We all love the simple explanations in life — that’s everyone’s bias, myself included — but ultimately it just doesn’t work here. That’s because of what hormones do in our body to those calories. Adrenalin and insulin have way bigger impact on metabolism than any calorie input you give your body from food, and this explains every problem anyone has ever noticed when they have tried counting calories (the research studies with issues here are in the 1000s).

This 10 min video from Dr Bikman explains some of the problems.

FWIW, I tell my athletes to focus on what matters. Training, quality food, sleep and stress control. In comparison to those, you’re wasting your time with calories. WRT food, focus on food quality that came from the Earth and eat when you are hungry to fuel your training and life. Simple.


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FWIW in the past I successfully implemented the following:

  • On inactive days my calorie burn estimate is about 2200, both from wearing a Fitbit about 10 years ago, and more recently wearing an Apple Watch. So that is my baseline.
  • add kJ of work from the power meter
  • add those two, and subtract 500 calories for a 1 pound/week deficit target. Thats what I would target for eating.

And that seemed to work fine. I’ve used that multiple times.

This year I took a slightly different direction, and I’ve been all-in on using the Apple Watch. I’m wearing the watch while sleeping to track HRV, and only take it off to charge while out on the bike.

Over the last 8 weeks I’ve been losing just under a pound a week, using a 500 calorie deficit a day target. No issues completing workouts on the bike.

Been using the Lose It! app for 50 days (got a congrats from the app this morning). Lose It is receiving calorie burn estimates from Apple Watch (I’m using RunGap app to sync Garmin biking kJ/calories to Apple Health, and Lose It reads from Health).

With that, here is yesterday:

Using my old method the calc would have been 2200+1500 = 3700 total energy burn. Using the Apple Watch it estimated 4412 total burn, which is +700 higher than my old method. Interesting.

And thats how I ate yesterday:

just slightly over budget my -500 calorie deficit target, yesterday was roughly -450 calorie deficit. Same same in my world view.

and macros:

Carb timing - Monday was a rest day, Tuesday I had something come up and didn’t ride but instead walked for an hour with my wife. Yesterday was 2 hour ride with ~45 minute at 90% ftp, so upped my carbs a little before the ride.

Summary. What I found interesting is that I’m eating more using AppleWatch/LoseIt than using my old simple math, but still losing weight and fueling performance.

Hope that helps.


How are you determining your BMR?

I’m bypassing it, given the variables I do know, I calculate TDEE directly (for everything else, except cycling).

@oldandfast Just so I understand correctly, you came up with this calculation in retrospect after the 32 days?
Were you trying to lose weight during that time and did you change your food intake including macros during that time?


I made a plan on day 0 and executed it. The plan included changes in macros. more protein and less carbs and more fats. I started working with the assumption that my TDEE was around 2350 and then ate about 1/2 of the kJ of the bike. Been training hard, feeling with good energy all around, but sort of surprised how much weight I’m losing.

I started working with the assumption that my TDEE was around 2350 and then ate about 1/2 of the kJ of the bike.

That is approximately what I’m doing as well. Trying to do a calorie deficit based on the fuzzy BMR/TDEE + half of the calories from the bike. I’m down about 10lbs so far this year but I have definitely not been as disciplined/consistent as I could be. I will say that my workouts mostly feel good which has not always been the case when trying to lose weight while doing a lot of endurance exercise.

I’ll be 50 this year and I’m currently 189lbs/85kg at 6’4/193cm at ~20%bf.

Congrats on the weightloss and keeping your energy levels up. You must have been in a deficit to lose the weight. Sometimes the body responds really well to changes in macros and adhering to a diet like yours. Some of that weight could’ve been water weight loss since you cut down on carb intake. If all things are kept equal now with your calculated tdee and macros - you should level out. If you increase carbs you could see the scale move up even without any visual changes. Another metric to consider is body measurements - often the body will change composition but the scale will be the same.
As far as ruining a nutrition plan goes it’s pretty simple - making changes to your current macros by increasing the calories to quickly can lead to a rebound. It’s best to make incremental changes if that is the direction your are going. Also, you would want to have about the same amount of time in a maintenance phase and keep your body weight steady to allow your body adjust to your current body weight and energy intake. Hope that helps.

It has been revealing how these changes improved my energy levels, sleep quality, performance……contrary to the carb patrol message….I mean, I still get plenty of carbs, whatever is not protein gets split 45/55 carbs and fats.

Thanks for chiming in!

I see that you dabble in the dark arts of low carb :joy:. Me too!!!

But refresh my memory, remember NuSi initiative?, there were a couple of strong studies circa 2015 that basically debunked the calories are not equal hypothesis. The Amstrong foundation pull out their money after those results.

At this point is only Gary Taubes sounding that alarm. Petter Attia moved on to make $$$ with concierge medicine.

I’m the last person to tell you to chug carbs on the bike, but have been surprised that increasing calories and carbs off-the-bike, versus a year or two ago, I’m still consistently losing weight and getting stronger (both muscle strength and endurance fitness/power curve). At sixty effing one. Go figure. And I appear to be under fueling, when referencing to latest recommendations for endurance athletes.


Yes - I dabble for sure. Dark side.

Sorry but don’t know the details of the studies you mention. Would like to read if you can dig up.

Here’s the background story and there are some links and information about the studies.