Stayin’ Alive - Resting Metabolic Rate

  • Last week I contemplated how many calories it would take to maintain my weight while leading a sedentary lifestyle.  The American Cancer Society’s tools suggested that I would need to consume over 3500 calories each day to stay at my current weight.  Wow, that seemed unreal but I decided not to stop there. 

     

    This week I searched for basic information regarding metabolism and how many calories are burned within my body if I simply do nothing.  What does it take to feed my body the energy it needs?  I wanted to know...

     

    What is Resting Metabolic Rate (RMR)?

     

    The Marquette General Bariatric & Metabolic Center answers this question.  "Resting Metabolic Rate is a measure of the number of calories your body needs just to stay alive. If you were to curl up on the couch all day with a good book, essentially “at rest”, there would still be metabolic activity being performed by your heart, lungs, brain and other body cells.

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    The most active cells in our body are those found in muscle. In a lean individual, skeletal muscle accounts for about 75% of resting metabolic rate. Muscle cells are the “energy hogs” of the body. Two people may weigh the same on the scale; however, the person with a higher portion of lean muscle will require more calories to maintain their weight.  Reducing caloric intake too far below resting metabolic rate causes the body to start to “conserve” calories."

     

    Can I easily calculate my own Resting Metabolic Rate?

     

    Another website I found, Calories Per Hour, explains the difference between Basal Metabolic Rate (same as Basal Energy Expenditure) and Resting Metabolic Rate (same as Resting Energy Expenditure) while providing a simple BMR & RMR Calculator.  However, they do recommend that a more accurate estimate of how many calories you need, or burn, in a day would be to consider the actual activities you perform in a 24 hours period.

     

    Some simple observations to keep in mind:
        * When your age goes up, your BMR and RMR go down.
        * When your height goes down, your BMR and RMR go down.
        * When your weight goes down, your BMR and RMR go down.

     

    This means that as you get older, shorter, and lose weight, your BMR and RMR will go down and you will need to eat less or exercise more to maintain your current weight.  Wow, it seems almost everything makes the metabolic rate go down, even eating too little.

     

    To use the BMR & RMR Calculator, you need to know gender, age, height, and weight.  Note that today I used 265 lbs as my current weight.  ;)

    • BMR & RMR Results (in calories):    1918 (BMR)        1868 (RMR)

    As BMR and RMR only represent resting energy expenditure or calories burned during a day of rest, an adjustment must be made to reflect activity level which can be done by multiplying by an activity factor listed below:

    • Multiply BMR by 1.200 for Sedentary: Little or no exercise and desk job
    • Multiply BMR by 1.375 for Lightly Active: Light exercise or sports 1-3 days/week
    • Multiply BMR by 1.550 for Moderately Active: Moderate exercise or sports 3-5 days/week
    • Multiply BMR by 1.725 for Very Active: Hard exercise or sports 6-7 days/week
    • Multiply BMR by 1.900 for Extremely Active: Hard daily exercise or sports and physical job

    Use of these activity factors produces a very rough estimate. For a more accurate estimate, calculate the actual activities that you perform as described on the Calculating Daily Calorie Needs page.

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    Why exactly do I need to know my Resting Metabolic Rate?

     

    Shape Up America!, a not-for-profit organization committed to raising awareness of obesity as a health issue and providing responsible information on healthy weight management, shares some simple ideas on this topic as part of their Shape Up & Drop 10™ program.

     

    When you cut calories to BELOW your RMR, your body fights back. Restricting calories below your RMR is like asking your car's engine to run on too little gas. If your car is sitting in the driveway with the engine on, it is burning gas as it sits there. If you put the car in drive and step on the gas, it burns gas at a faster rate. What happens if you choke off the supply of gas to your engine? It sputters and eventually stalls. The same is true for your metabolism.

     

    When you restrict calories too severely, your body is forced to make tradeoffs. Your body will struggle to preserve the highest priority bodily functions. Brain and heart function will be a very high priority whereas reproductive function and bone will be sacrificed.  Shape Up America! also offers a Resting Metabolic Rate Calculator.

     

    Bottom line: I think that the message is clear that I should not try to lower my daily caloric intake much below 1900 calories if at all.  I certainly don’t want to sacrifice any brain or heart functions at this time.  But I’m sure that this still leaves plenty of room to eat less and more healthily.

     

    January 24, 2010
    Weight:   265.2 lbs
    BP:         134/88
    Pulse:     70

     

    January 31, 2010
    Weight:   264.6 lbs
    BP:         125/79
    Pulse:     64

     

    So tell me, what is your Resting Metabolic Rate and does knowing it affect your decisions in watching what you eat?

     

    Lisa Emrich is author of the blog Brass and Ivory: Life with MS and RA and founder of the Carnival of MS Bloggers.

Published On: February 01, 2010