Calculating your metabolic rate

Q. How accurate are the various methods of estimating Resting Metabolic Rate? After checking several calculators, I had my RMR tested using a mask that measured oxygen levels for 20 minutes while I read a book. It resulted in an RMR of 720. I was expecting it to be closer to 1200. I'm very confused now.

A. According to this post by our resident fitness expert, Steve Cabral, the test you had done is fairly accurate when properly administered.  So, I'm also a bit surprised at the discrepancy between your test results and the various calculators.  I wonder if it would be worth having it retested.

Obviously, RMR calculators, which take into account your size, age, gender and body composition, can only provide an estimation of your true metabolic rate. For most people, though, these estimates are pretty close. This article explains other factors that can affect your RMR and estimates your RMR using 5 different formulas. When I plugged in my data, all five calculators estimated my RMR within 100 calories.

To estimate how many calories you actually burn in a day, our Daily Needs Calculator starts by estimating your RMR and then estimates how many calories you expend in your normal daily activities, plus exercise, plus a relatively small number of calories attributable to the thermic effect of food (which is bascially the energetic cost of converting food to energy).   The resulting figure is an educated guess about how many calories you expend, which can help you gauge how many calories you should be consuming. But short of going through every day wearing an oxygen/CO2 mask, there's no way of knowing your exact calorie expenditure.

It's tempting to think of the human body as a machine, for which we can simply calculate a "miles per gallon" figure. And in a way, it is a machine, but one so complex that it resists reduction to simple formulas.  In his book Good Calories, Bad Calories, Gary Taubes argues that attempting to manage our body weight by manipulating the calories in/calories out equation is a waste of time anyway, because the body will recalibrate its engine to compensate for changes in input and output. Taubes holds that it's the type of fuel, not the amount, that determines fuel efficiency.

So, I guess my point is that the calculators are merely a way to get you on the green. Once there, you've got to get out your putter. And by that I mean that despite your best efforts to figure out how many calories you should be eating, you may need to adjust that if you find you are gaining or losing weight when you don't expect to.

Anyone else have any experience with RMR testing?