During the entirety of my weight loss, I have been really curious about my activity level, or to put it another way, the "calories out" portion of the CICO equation. So, I decided to do a deep dive into the data I've been collecting on myself, to see what my activity levels REALLY were, and share the results with all of you. It's a bit of a long post!
Before we start, here are my stats: 33F 167cm/5'6" SW: 127kg/279.4lbs CW: 97kg/213.4kg. I've been logging my calories since the beginning of August 2018.
So, most of us here know what our CI (calorie in) is: we log and track our intake in MyFitnessPal/Loseit/etc. And, most of us here ALSO know that fitness trackers and exercise equipment is not very reliable to determine our calorie burn (our CO/calories out). So, what most of us suggest is that we set our calorie limits to sedentary, and be very cautious with eating back "earned calories" that our apps and fitness trackers tell us we burned during the course of a day. Before I go any further, let me just say: this is a good strategy! I did this from August through December 2018, because I didn't have a fitness tracker/way of estimating CO. I did just fine during that time period, and lost plenty of weight.
I got an Apple Watch for Christmas, however, and that really motivated me to see if I could peek inside the black box of my metabolism, and see what was really going on. I started using the 3-Suns Adaptive TDEE Spreadsheet to see what was really going on with my TDEE (calculating it myself, instead of relying on My Fitness Pal's calculations for me at sedentary). I wanted to see how my calculations of my TDEE compared to my Apple Watch's measurements.
In January 2019, I started swimming 3 times per week. My Apple Watch says that I did 27 workouts that month (including walks, or whatever else I was logging with it), for 15 hours and 45 minutes of total workout time (with the average workout lasting 35 minutes). Everything sounds good here, right? ~16 hours of work-outs is about 3 hours per week! Sounds like what "lightly active" on the calorie calculators say! Apple Watch told me I was killing it, and burning 5-700 calories per swim! My weight loss didn't track with those really high numbers from the Apple Watch, however. My calculated TDEE from the spreadsheet showed my workouts were boosting my TDEE by about 100-150 calories (maybe they just weren't intense enough!). I'm glad I kept eating at my "sedentary" calorie allowance, because jumping up to "lightly active," would have been a mistake.
During the month of February, I kept swimming, kept wearing my Apple Watch, kept collecting data, and, by the end of the month, had a new job. That job was (and still is) to be a mail carrier, by bike. That means, in a week, I walk/bike about 13-14 hours just to deliver the mail. I also commute to work by bike (~10 minutes each way). So now, in an average week, I am doing an active job (or commuting back and forth from it) for about 15 hours. It's not particularly high intensity, but, as the data shows, the duration matters.
This is the first graph I made, showing what my Apple Watch thinks my TDEE is, what I calculated my TDEE to be (through the 3-Suns website), what Apple Watch thinks my "sedentary"-activity level TDEE is*, and what my BMR is (using the Mifflin St. Jeor formula). *Just a note: Apple Watch breaks up activity measurements into "move calories" and "resting calories. "Resting calories" are "an estimate of the energy your body uses each day while minimally active. Additional physical activity requires more energy over and above Resting Energy (see Active Energy)." So, without the Apple-ease, "resting calories" are supposed to be your sedentary TDEE. "Active Calories" are, as defined by Apple, "an estimate of energy burned over and above your Resting Energy use. Active energy includes activity such as walking slowly, pushing your wheelchair, and household chores, as well as exercise such as biking and dancing. Your total energy use is the sum of your Resting Energy and Active Energy).
In that graph, you will see that Apple wildly overestimates my "Active Calories" (yellow). What I would have expected to see (if the Apple Watch were very accurate) is that the green line (sedentary TDEE/Apple Watch "resting calories" would be about 200 calories higher than the red line (my calculated BMR). Likewise, I would have expected the blue line (calculated TDEE from the 3-suns sheet) to be about the same as the yellow line (Apple's "Active Calories). That was obviously not the case. What is clear to see, however, is that in the first months of wearing my Apple Watch, it measured my "resting calories" (green line) fairly close to what my actual TDEE was (blue line). After my job started, in the end of February, however, my calculated TDEE goes above Apple's prediction for "resting calories," but stays well below Apple's predictions for my "Active Calories."
Although it looks like my Apple Watch is slowly getting more accurate, it clearly isn't very accurate right now. So, I made a second graph, to plot my calculated TDEE (3-suns sheet) against what Mifflin St. Jeor would predict at 3 activity levels: sedentary, lightly active, and moderately active (what most of us are choosing from while making our calorie allowance budgets). The results were interesting.
Prior to getting beginning my job (when I was just swimming 3x/week), my calculated TDEE tracked pretty well with "lightly active," but was definitely still below it. Glad I was careful with eating back "exercise" calories! After starting my job, however, there is a clear spike. I'm not quite "moderately active," but my calculated TDEE definitely puts me a little above "lightly active." I have to admit, I thought for sure that ~15 hours per week of walking/biking would put me squarely in "moderately active," but, it's just not the case!
I'll keep collecting data on my Apple Watch, and keep minding my calorie budget for now. I hope that my experiences and data from my Apple Watch helped someone out there: while closing the rings are motivating, and the monthly challenges can be fun to accomplish, in my experience, the Apple Watch really shouldn't be trusted to calculate a reasonable TDEE. However, the trusty ol' Mifflin St. Jeor equation, in conjunction with my own data/TDEE spreadsheet, has been really interesting, and quite accurate!
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