Burning Calories as I Lose Weight

One thing I’ve been struggling on lately is getting my daily calorie burn up higher.  In January, I averaged burning 1786 calories a day per Fitbit.  Between January and April that was my highest month, but even my lowest was 1656 calories a day (at a time when I didn’t exercise as much due to my leg/knee issues starting).  But, since June I haven’t cracked a daily calorie burn above 1500 calories.  Now, I know that part of this is because I’ve been less active.  First, I got out of the habit when I wasn’t allowed to even walk due to the trabecular bone injury.  Second, once I could walk again I’ve been cautious not to overdo it.  Still, even on days when I do exercise I don’t usually get above 1600 calories.  Last Friday, for example, I was out and about during the day and exercised on the bike.  Weight Watchers gave me 4 activity points for the day based upon the data it received from my Fitbit.  But, according to Fitbit, I burned only 1584 calories!

I recognize that as I lose weight, I do burn fewer calories as I have less of me to move around.  What I’m realizing now is how dramatic that difference really is.

For example, here is an example of a day from January where I was very inactive.

Fitbit 1-7-2014

I only took 1509 steps and no activities were recorded for the day.  Fitbit said I burned 1546 calories which was very low at the time.  For example, during that month I had lots of days where I burned 1800 to 2000 calories a day, and a couple where I went over 2000.  The Friday before January 7th, I weighed in at 185.8 pounds.

Contrast that with a similar day in early September.

Fitbit 9-9-2014

I took 1552 steps and burned 1423 calories.  The Friday before that day I weighed in at 162.2 pounds.  So, there was a 23.6 pound difference.  And I burned about 120 calories a day less when I weighed less.

I went back and compared several other recent sedentary days to Fitbit records for past sedentary days when I weighed more.  Sometimes the difference wasn’t as much as 120 calories, but other times it was more.  I also compared a few recent days to back in August 2013 when I was in the 190s.  For example, there was a day in August when I walked 1325 steps and burned 1555 calories, versus a day in September when I walked 1334 steps and burned 165 calories.  Or, to even more depressing, a day in September when I used the exercise bike for 40 minutes (4303 steps — some of which were from the time on the bike) and I burned 1527 calories versus that day last August when I burned 1555 calories and basically sat around all the day.

The amount that I burn now compared to when I was in the 190s or the 180s varies somewhat but it seems to be somewhere around at least 100  to 120 calories a day less now than when I weighed 20 to 25 pounds less and around 160 calories or so less than when I weighed 30 pounds less.

I’ve played around with some of the Basal Metabolic Rate calculators.  Using this one, I plugged in my data for when I weighed 185 and it says my Basal Metabolic rate using various formulas was:

  • Mifflin- St Jeor  formula – 1401
  • Harris-Benedict – 1484
  • Katch-McCardle – 1351 (based upon body fat of 46%)

My current numbers based upon my last weigh in of 160 pounds (note I’ve had a birthday since January so that is factored in as well):

  • Mifflin- St Jeor  formula – 1282
  • Harris-Benedict – 1371
  • Katch-McCardle – 1281 (based upon body fat of 42%)

The first 2 formulas would say my basal metabolic rate now is about 113 to 119 calories a day less now than it was in early January.  The Katch-McCardle formula takes body fat into consideration and says the difference is only 70 calories less now than before.  It comes up with a sharply lower BMR than the other formulas because of my high body fat percentage.

It makes sense to me that if you have high body fat you would have a lower BMR than someone with a lot of muscle and low body fat.  So, I like to use the Katch-McCardle formula.  But, of course, most people don’t know their actual body fat percentage.  In my case, I have a Withings scale that gives a body fat percentage.  But, it jumps around a lot so I don’t put a huge amount of faith in it.  I will say that I always seem to lose less weight overall than Fitbit says I should lose. That is, my calorie deficit per Fitbit doesn’t usually translate to losing that much weight, even after averaging it out over a few weeks.

One reason is that I believe that Fitbit uses the Mifflin-St Jeor formula (I’ve read this at various places but don’t know for sure).  And, when I was 46% body fat that formula showed a burn of about 50 calories a day more than Katch-McCardle would show.  Now, with a body fat percentage around 42% the two are almost the same.  It will be interesting to see if my Fitbit calorie deficit becomes more accurate at predicting my weight loss.  It seems to be getting a bit more accurate over time, compared to earlier in the year but I’m not entirely sure yet.

Regardless of which calculator I use, though, the point is that I am burning at least 70 calories a day less  when I’m doing nothing than I was in January.  And, when I do engage in activity my body is smaller so I don’t burn as much as I did back then.



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