If you listen to what some experts have to say, you’d think your metabolic rate is the end all be all of health and weight loss. However, just like everything else the truth is a lot more boring than you’d think.
Your metabolic rate is simply the amount of calories you burn on a daily basis to support the regular functioning of your body. There are different ways to measure it but the most common and the one that is most applicable for you is called your Resting Metabolic Rate or RMR for short.
Your RMR is the amount of calories you burn just sitting around relaxing and not exercising. This doesn’t include walking or moving around or working out, it doesn’t even include fidgeting. It’s just the amount of energy you burn up sitting around doing nothing. Unfortunately for many people this describes their activities every day.
So how do you calculate your RMR?
Well we can’t calculate it exactly without multiple trips to a scientific lab, so the best we can do is an estimate (and scientists are still just learning what average resting metabolic rates might even be).
Let me repeat that, the best we can do is ESTIMATE your RMR. Any metabolic rate calculator you find online is just an estimate, and many of them are way off and in need of a serious update.
In research done by Amanda C et al in 2010 the RMR of 47 women was measured and compared it to the popular RMR estimator equations. The average RMR for this group of women was 1027 calories per day. The average height of the group was 5’5.
Interestingly the predictive equations all overestimated RMR, and the worst one (harris benedict) overestimated by 700 calories! It’s tough to hear it, but we all just need to eat way less calories than we’ve been led to believe.
One of the major areas where popular online metabolic rate/calorie burn calculators breakdown is when they add in their ‘activity factor’ calculation. Most of these calculators overestimate the amount of calories we can burn from activity.
This is because the research they are basing their equations on is very old and outdated. These outdated activity factor equations were done on people who were much more active than we are today (think full time lumberjacks).
METABOLIC RATE – Getting rid of some erroneous Myths
You’ve probably been led to believe that lean people have high metabolism, and that most overweight people have slow metabolism. Turns out this is a major false assumption. It’s just flat out wrong.
In further research done by Ravussin et al in 1982 it was shown clearly that the obese people actually had higher resting metabolic rates than the lean control group.
The average metabolic rate of the obese people was measured at approximately 1800 calories per day as compared to 1450 calories per day for the normal weight control group (and the obese group was actually shorter on average than the controls so we would guess based on height that their metabolic rate should have been lower if all other things were equal).
The difference in metabolic rate was because the obese people actually had an average of 30lbs more total Fat Free body Mass than the lean people. This doesn’t mean they had 30lbs more ‘muscle mass’, but rather more of everything including organ mass, bone mass, and residual tissue mass (of which a small amount might have been muscle tissue).
This leads perfectly into another false assumption about your metabolic rate – that your muscles are the biggest contributors to how many calories you burn in a day.
It turns out that out of all these tissues the ones that contribute the greatest proportion to your metabolic rate are your internal organs.
Research by Muller et al, In 2011 shows that not only do your internal organs contribute the largest portion to your metabolic rate but that they scale to the height of your body and to the overall size of your body. In other words, the taller you are and the bigger you are the bigger your internal organs are and thus the more calories they burn.
The following is a list of the relative amount of energy each tissue contributes to your daily metabolic rate per poundof each tissue (data from Bosy-Westphal et al 2009):
Heart = 200 cals/lbs
Kidney = 200 cals/lbs
Brain = 110 cals/lbs
Liver = 90 cals/lbs
Muscle = 6 cals/lbs
Fat = 2 cals/lbs
Bone = 1 cals/lbs
As you can see from this data, your heart, kidneys, liver and brain are the most highly metabolically active tissues in your body and as you will find out they actually contribute the most to your metabolic rate. Muscle is actually much closer to fat when it’s at rest, it really doesn’t burn many calorie when you’re not working out.
Research by Heymsfield et al. in 2002 indicates that approximately 69% of your resting metabolic rate comes from your internal organs (specifically the combination of your heart, liver, kidneys, and brain). The other 31% comes from your bones, muscle, and fat tissue.
I’m presenting this research to show you that striving to add extra muscle isn’t going to increase your resting metabolic enough to change how many calories you can eat to lose weight. I’m also showing you that your metabolic rate is likely lower than you were lead to believe.
There is one final false assumption we have to discuss and that’s the effect of exercise on your metabolic rate. Now, let me say right here that exercise is one of the best ways to control how many calories you burn in any given day.
There are hundreds of research papers and dozens of textbooks on this topic. There are also dozens of metabolic rate calculators online and equations in textbooks that will suggest an ‘activity factor’ that suggest you can burn anywhere from 500 to 2000 extra calories per day just by being active.
In all cases these are best guesses, and I’d say rather optimistic guesses in many cases… you’ve got to be super mega active to actually burn 2000 extra calories in a day! For example if you weighed approximately 175lbs you would need walk for approximately 6 hours to burn 2000 calories.
Or you would need to do approximately 3 and half hours if high intensity interval training. In both cases I’m pretty sure you already shaking your head thinking ‘no way’. And you would be right. This would be total insanity to attempt to burn 2000 calories in a day. Heck even 1000 extra calories would take hours and hours of exercise.
In fact, we cross referenced the actual measured true calorie burn for various activities and exercise from scientific research and compared it to what most metabolic rate and activity calculators suggest.
What we found out was that most calculators grossly overestimate daily calorie burn for most people. This is because the metabolic rate calculators are assuming that an ‘active’ person is doing MULTIPLE hours of activity EVERY DAY, not just a 45 minute workouts 2-3 times per week.
The truth is that most of us don’t even do 1 hour of vigorous activity per day let alone multiple hours. In most cases the only excess calories we will burn in any given day is due to a scheduled workout…and if you don’t even do that, well you are sedentary plain and simple.
If you sit at a desk all day, and do little or no exercise then you are sedentary by any definition. This means that you should click the ‘sedentary’ option every time you attempt to use any online metabolic rate calculator.