Burning?! 3500-5000-9000 calories per day,

[oepl]

i try to burn at the very minimum 3500 calories per day which is a thousand more than BMR, but in the last two weeks i have burned between 5000-9000. I'm 6"3 140kgs 100kgs is lean muscle (Dexa Scan) so i'm about high 20% body fat percentage. Goal- I want to get myself back to about 120 which is very lean for me, i know i'm a big bloke but these calories can't be right and there is not a chance i'm eating a traditional 600 calorie deficit. I try to eat about 1500 calories a day unless i burn 8-9 thousand calories and feel exhausted then i usually try to beef up my protein. I'm on a keto diet. i feel tired and sore which is to be expected (not crazily exhausted), i exercise a lot and i'm very active, i have a lot of sport in my history which provided me a very good base and attitude towards training. My question is am i doing damage from how much i'm eating to calories burned? Also is the fitbit calculating calories from total body weight which might skew actual calories burned( because i'm so much bigger than average fitbit user), or does it work out lean body mass?

[OnlyRunning]

I do not believe you are doing any damage to your body. However, you will be very tired and exhausted at the end of the day. If I were you, I wouldn't burn so much calories or I would eat more foods that are high in calories but still healthy.  

[Dominique]

Very unlikely your actual energy expenditure is 5000-9000 calories per day (regardless of what your Fitbit reports), even taking into account size (which Fitbit does), or lean mass (which it doesn’t). Especially if you’re only eating 1500 calories at the same time.

For estimating BMR, Fitbit uses the Mifflin-St. Jeor equation. If you wanted something that would take into account lean mass, you would have to use the Katch-McArdle equation. Not that this would result in a huge difference (you can check it with your numbers using online calculators) anyway.

[emili]

do you have a tracker that has the HR function? Although it will not be completely accurate it is closer than those that measure based on step count and your information. I also don't know what you mean by damage? To what? If you are hungry, tired, lethargic, dizzy or just out of sorts, then you are not getting enough nutrition or your diet is not conducive to how much activity you are doing. I think maybe take a step back and really figure out how high your deficit should be, what nutrition will align with your calorie intake and support your active lifestyle and the rest is measured by the scale and clothes... whatever you decide to do, I would do something, being tired often is not a great way to go through the week... 

[Mukluk4]

Without seeing your profile data (activity breakout that shows active vs. very active) or a detail into what you consider as "exercising a lot" and "very active" it's very hard to tell what is accurate.

I'm 6'1" and right around your goal weight of 120 kg.  Assuming it's not a day where I deliberately take off due to weather or doing something with my kids, I try to burn at least 3800 calories (on the fitbit reading) and currently averaging about 4200 a day over the past 30 days.

As far as activity to get there:

Planned 

MWF - Weight room, 4-5 km jog, some intense pylo activity

T/TH - Morning basketball (roughly 1 hour)

I'm also on a short list for a group of guys that play pick-up a few evenings a week and try to get my boys out in the yard playing some type of sport when the weather holds.

I've personally broken 6k calories a few times and that burns me out to where the next day I have to take it pretty light.

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Now the important part.

Calorie tracking on activity trackers are very spotty. 

If you don't have an HR monitor it takes your steps x stride length to determine pace and distance which then charts to a calorie burn (if you don't believe me double your stride length in the options and watch those calories fly)

For HR monitors, it assumes the standard HR zones which can inflate or even deflate your caloric burn.  Studies have found that these trackers can be off as much as 20%.  

[oepl]

yep my fitbit has a heart rate tracker, its the current charge 2. i put the heart rate tracker on all the time as well. i run my own landscaping company, so currently im forever digging holes and shifting dirt, so id say a very active job. training wise i use do 30mins heavy weight not too much rest and either hiit cardio or circuit for another 30mins. usally try and get a walk in 1-2hrs few times a week.

[oepl]

damage as in going to far on a calorie deficit`

[Dominique]

Excessive caloric deficit (especially over too long a period) results in excessive/unwanted metabolic adaptation, which is sometimes called "metabolic damage". You can assess whether or not your deficit is excessive by looking at your average weekly weight loss: a common recommendation is to lose no more than 1% of your body weight per week in average. In your case (with your starting weight of 140 kg), that would be 1.4 kg per week. If you’re losing much more than that, chances are your caloric deficit is excessive. 

If you were losing 1% of your body weight per week in average, you would be 124 kg after 12 weeks, i.e. not too far from your self-stated goal.

[Shanejgeist]

The damage I would be worried about would be to your  metabolism. If you are burning 5000 calories and only taking in 1500 that will slow your metabolism down so if you ever increase your calories it will be difficult for you to maintain weight. This is a big reason why a lot of people with extreme weight loss end up gaining weight back, their metabolisms are shot.