Metabolic Rate: How many calories do I really need?

Recently, several questions from friends, along with a pretty preposterous post on another forum, prompted me to do some research into an area I hadn’t looked into in a while: BMR (base metabolic rate) or RMR (resting metabolic rate) is the rate at which your body burns calories when you’re doing nothing at all.

I have always accepted as fact that muscle burns calories even while resting. Recently, I read an article that stated that a pound of muscle will only burn 4 extra calories per day, a pretty small amount. They quoted some obscure reference, but the article was counter to everything I had ever read. I did a search on the topic and came up with about 4 more articles all stating the same thing and all quoting the same research (for more on this phenomenon, read my article: “Don’t Die of a Misprint”).

I can only assume these authors are Richard Simmons fanatics that are upset at how low their testosterone has plummeted from doing too much cardio and wearing pink shorts. It didn’t take me long to find out how incorrect they were. They had picked out a little bit of theory that supported their point of view, and ignored any other evidence to the contrary.

To get to the answer, I need to explain some theory on BMR. For many years (going back almost a century) scientists have been looking for a formula to predict BMR. Most have been based on Body Mass, Height, Age and Gender. Variations of this basic formula have existed since 1919. However, the formula has had to be revised over the years due to some unknown factor that was changing. The basics of the human body haven’t changed in the last 100 years, but what has changed is the amount of muscle the average person has (due to our currently inactive lifestyles.)

Recently, a new formula was derived. This new formula is more accurate for individuals of all types, and is also simpler: It has only one variable LBM (Lean Body Mass = Muscle).

BMR = 370 + (21.6*LBM)

Where LBM = (1-Body Fat percent)*(Body Mass in Kg)

You may not care much for the math, and may never even care to calculate your BMR, but there are some interesting conclusions we can come to based off the data that generated this formula:

First, short of very rare diseases, your BMR is almost entirely determined by how much muscle you have. Based on the data that generated the formula, muscle uses 21.6 calories per day per pound, not 4 as quoted in the articles I spoke of, and the rest of your body accounts for about 370 calories per day regardless of how big you are or what gender.

This isn’t theoretical, it’s what the researchers tested in thousands of individuals. This means that in one year, one extra pound of muscle will burn over 7600 calories, or over two pounds of body fat. If you consider that the average American puts on 1-1.5lbs of fat per year, you begin to see just how significant a couple extra pounds of muscle can be for your long term weight maintenance!

The next fact we can derive from this research is that neither height, age, or gender affect BMR. The fact that height really doesn’t matter shouldn’t surprise anyone. Age is also no big surprise. You’ll often hear that our metabolism slows down as we age. This is not true to any great extent. Our metabolism slows down as we lose muscle, and since the average seditary American loses muscle as they age, the metabolism slows down. I personaly feel that this misrepresentation of the facts by many health care practitioners does us all a great disservice: What most American’s have been told is normal, may be average, but not normal in any physiological sense.

How about gender? I see the commercials all the time that tell women they are different from guys. They don’t lose weight as easily, or need pills made specially for them. Although there are certainly many difference between men and women, metabolism isn’t one of them. Putting on a couple extra pounds of muscle will help a woman just as much as it will help a man. The smaller amount of muscle many women start with only makes the effect more pronounced. Sorry girls, despite what the commercials tell you, your base metabolism works the same as it does for guys.

If you want to finish calculating how many calories you burn on a daily basis, you have to multiply this amount by your activity multiplier:
• Sedentary = BMR X 1.2 (little or no exercise, desk job)
• Lightly active = BMR X 1.375 (light exercise/sports 1-3 days/wk)
• Mod. active = BMR X 1.55 (moderate exercise/sports 3-5 days/wk)
• Very active = BMR X 1.725 (hard exercise/sports 6-7 days/wk)
• Extr. active = BMR X 1.9 (hard daily exercise/sports & physical job or 2X day training, i.e marathon, contest etc.)

Once you have your total calories, you can subtract some number of calories (say 500 for a 1lb a week weight loss) and get your desired calories per day.

Of course, that factor introduces a large amount of error into the equation. Let’s say your BMR is 1500 cal/day and you use the “Mod. Active” factor when you’re really “Lightly Active”. That error would introduce a calorie error of 370 calories, which would be enough to cause you to lose far less weight than you thought you should, but at least it’s a starting point.

Calories Burned During Exercise:

I hear it all the time: “I did the elliptical today and burned 1000 calories.” People use the number on the machine to justify all sorts of bad dietary practice. Unfortunately, those numbers tend to be fairly inaccurate. I’ve found various elliptical machines tend to be the worst offenders but all the machines are off to some extent.

Why would the companies do that? The answer is: to sell more machines. People tend to use the machines with which they can most easily burn the most calories. Gyms buy the machines people use the most. Personally, I feel this is the entire reason for the popularity of elliptical machines: They burn very few calories for the amount of motion going on (hence are actually not much of a workout), yet the indicated calories tend to be very high. You get the best (or worst) of both worlds: an easy workout that APPEARS to burn a lot of calories. In most gyms, the stairstepper machines tend to be the last to be used, yet this machine BY FAR provides the best workout, and best use of your cardio time.

It seems that virtually all machines tend to exaggerate a little bit, so I wouldn’t trust any of them to justify that post workout Ice cream Sunday. If you want to get an idea of how many calories an activity will burn for a specific amount of time, try this calculator:

http://www.primusweb.com/fitnesspartner/jumpsite/calculat.htm

Although even this calculator and ones like it have two issues. First, they include BMR (Base Metabolic Rate) calories in the results. If it says you’re burning 500 calories for a particular activity, but you would have burned 80 calories just sitting on the couch, then you really only burned 420 doing the activity. Including the BMR calories will cause you to basically double count the BMR calories.

The second error in these calculations is the lack of accounting for post exercise energy expenditure. This is the amount of calories burned after you’re done exercising. For running, biking or virtually any other steady state activity, this is virtually zero. For intervals (sprints), real mtn biking, weight lifting, or any other very high intensity activity, this can be up to three times the amount of the calories burned during the activity itself.

So, even though the calculator says you will only burn 300-500 calories in an hour of weight training, if you do it with enough intensity and are strong enough and experienced enough to lift some heavy weight, your total calorie burn over the course of 48 hours will be upwards of 1000-1500 calories. It is also the reason why doing intervals (sprints) instead of steady state cardio will result in up to three times the total calorie expenditure as steady state cardio.

This, of course, is the basis of why I always recommend weight training combined with interval cardio as the most time efficient method of losing weight.

I also get a lot of questions about whether we should do cardio on an empty stomach or not. Just as with the “Fat Burning Zone” on the heart rate label on the machine, when it comes right down to it, it still only matters how many total calories you consume and how many total calories you use. It really doesn’t matter if you burn body fat while you’re exercising, if you’re just going to put it right back on by eating more the rest of the day.

The two factors that should really affect your decision to do cardio on an empty stomach are as follows: First, can you get a good workout when you’re body is in a fasted state? If the intensity of your workouts is suffering because you don’t have the energy, then exercising on an empty stomach is probably a bad idea for you. The second factor is whether or not you’ll just eat more the rest of the day to compensate. If you do your cardio on an empty stomach but then are SO hungry after your workout that you scarf down twice as much as you would otherwise, then all that fat is just being replaced anyway.

You have to always remember, that fat cells are like little gas tanks: burning fat doesn’t destroy the fat cell. Once your body makes more fats cells, they’re with you for life. Your body is very efficient at using the fat for fuel and then refilling the fat cells once you eat. It is very possible to do workouts that use very little fat for energy WHILE you’re doing the workout, yet cause greater fat loss OVERALL.

You can use the information in this article to calculate how many calories you’re using, and then adjust your food intake accordingly. Just remember, it’s REALLY easy to fool yourself. A little fudging here and there, and the calculation is worthless. Ultimately, the best way to adjust your daily calorie intake is by monitoring your body fat or at least your weight loss (or gain if you’re trying to put on muscle), and adjusting accordingly. The real usefullness of this information is more in how it helps you understand how your body is using calories.

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