Food Matters: Calculating your metabolic rate

By Chuck NewcombMarch 5, 2012 

Dear Chuck, I would like to find out how many calories my body burns. Is there some way calculate or to test what my metabolic rate is? Josh

Dear Josh, everyone has a unique amount of calories (energy) they burn through the day. There are basically two parts to the calorie burning question. First, it would be good to know how much you burn just for taking up space on the planet and using the air you breathe. That is the Basal Metabolic Rate (BMR), the energy burned to live, breath, pump blood and to think. That is a pretty fixed rate that will stay the same no matter what you are doing.

Then there is the variable activity rate, the energy you burn with the exercise and other regular daily activities like walking, cleaning, working, eating, etc. This can change by hundreds of calories from day to day. This rate can also change with stress, injury and illness. Exercise not only helps you burn more energy but it helps to maintain or increase muscle mass which then increases the metabolic rate up to 15 hours after the exercise is completed.

Your BMR is affected by gender, age and the amount of muscle you have compared to body fat. The BMR for males is higher than females because of testosterone. Infants and growing children or teenagers have higher metabolic rates than adults because of growth hormone. The BMR for males is fairly consistent until about age 70 when testosterone levels drop off. The rate for females increases during pregnancy and is even higher when breast-feeding, but drops when they go through menopause.

The most accurate way of measuring total metabolic rate is to put you in an enclosed chamber and measure the amount of heat you produce over a period of time. That heat is measured in calories. Another more practical way is to wear a mask that is connected to a machine that measures the amount of oxygen consumed. Both of these methods are pretty impractical.

An easier way is to figure out your metabolic rate is to do a calculation using age, sex, height, and weight in the equation. For an even simpler method, use weight in pounds and multiply by 12, 14 or 16 depending on age and activity. A 150 pound person, 40 years old might need about 2400 calories per day. The older you are the lower the number. The more active you are the higher the number.

For those that are overweight it is a good idea to use Ideal Body Weight (IBW) to do the calculation. To figure out the IBW for females figure 100 pounds for the 5 feet, and 5 pounds for every inch above 5 feet. A woman 5 feet 5 inches tall would ideally weigh 125 pounds. Males would be 106 pounds for the first 5 feet, and 6 pounds for every additional inch (e.g. 166 pounds if they are 5 feet 10 inches).

The best way to figure out if you are getting too many or too little calories is to see if you gain or lose weight. Too little calories and you obviously lose weight. Too many calories and you gain weight. So, balancing food and exercise is important to maintain a healthy weight. It doesn't really matter if you actually know you need 1500 or 3000 Calories per day. What matters is what you individually need. Don't be surprised if you are totally off in your estimations.

Chuck Newcomb, MS, RD, CDE is a consulting Registered Dietitian currently providing medical nutrition therapy services for Memorial Hospital Los Banos. He has a Masters of Science in Clinical Nutrition from New York University. E-mail questions to the Attention of ChuckRD at: MHALosBanos@SutterHealth.org or on his website MySmartRD.com.

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