I finally did resting metabolic testing, this process is where you breath into a monitor for 10+ minutes and it uses the oxygen conversion % to measure your actual metabolism at rest. There were a couple interesting take aways:
First, and a sad one, for me it confirmed what I was already pretty sure of: my metabolism is far lower than expected. My expected RMR is 2150, my actual RMR is 1650. So if I ate what I was supposed to calorie wise to maintain weight I would gain roughly 50 pounds a year (which Ive done at least 4 times in adulthood). I had pegged it around 1700-1800 so this wasnt a shock, but it’s also nice to know for sure.
Second, I was at the University of Texas lab and the person doing the test was a professor, he said he “never trusts a single reading”, he requires two matching readings back to back to feel confident, and we ended up doing 4 readings (tests 3-4 matched, with 1-2-3 the measurements went down each time as I got more relaxed).
Third, I really wish I had earlier data from my life. I believe my metabolism has always been slow, but I also suspect that dieting habits, losing 100 pounds when I was 18 and having consistent low calorie intake for years to maintain triggered my body to stay in permanent “famine mode”. One of the biggest take aways with “theremogenic adaptation” studies is that consistent caloric deficits will often trigger the body to further restrict metabolism beyond the lower caloric use expected from the lower weight. Most people when they return to consistent non-deficits will return to close to expected RMR in 6-12 months or so but some individuals never do. I think Im one of the “permanent adapters”, but I dont know for sure, and likely wont ever. I have about 8 more months of weight loss at my current rate, I will try to do a retest in another 18 months or so once Ive been done with weightloss for 6 months
My guess is that your muscle mass is relatively low for your BMI due to the lifetime of weight loss cycles you described. In other words, you’re less muscular than the average person with the same BMI. So, your RMR is lower than expected.
RMR is the body at rest, those are the calories your burn just not doing anything except laying there relaxed. But what about TDEE?
TDEE is usually what I think of when someone says their metabolic rate is above 2000. I mean, burning 2000 calories without moving is quite a lot, so 1600 for a RMR sounds like a really good number to me? You can burn 1600 calories just resting and relaxing? I wish!