The Most Accurate Way to Measure Your Metabolism

By , SparkPeople Blogger
If you're like most people who are struggling to lose weight, you've started watching what you eat and counting (and cutting back) on your calories. We all know that weight loss is the result of a simple equation: burning more calories than you take in each day. But how do you know how many calories you REALLY burn—or how many calories you should be eating for optimal weight loss?
We all have our own unique metabolic rates—the amount of calories our bodies use just to stay alive; this is called your resting metabolic rate (RMR). Even at total rest—and without moving—your body is using ("burning") calories just to breathe, circulate blood, digest food, think, blink and more. This actually takes more calories than you might think—hundreds or even thousands. On top of your RMR, even if you don't work out, you burn additional calories by performing basic activities of daily living: brushing your teeth, typing on your computer, and driving your car.
When you visit most nutritionists, sign up for a free weight-loss plan at, or even follow a diet plan you read about in a book or magazine—you're getting some good estimates of your calorie needs, usually based on your weight, gender and possibly your age and height. But these widely used formulas are just that—estimates. They are reasonably accurate for a lot of people, but they are not always accurate for everyone. "Calorie Plan A" may be too few calories for you but be perfect for your sister to lose weight. "Calorie Plan B" might not cut calories enough, yet be too many calories for your friend who weighs the same amount you do. Since we are all unique, estimates don't always work. And when they don't, it can stall your weight loss or bring it do a grinding halt despite your efforts of tracking, counting, measuring and eating within a specific calorie range.

"There are a few people who really struggle in determining their accurate weight-loss calorie range," says SparkPeople's head dietitian, Becky Hand, RD, LD.  "They just don't seem to 'fit' the standard formulas, and 'experimenting' with their calorie intake brings about more and more frustration."
So what's a person to do? You can tweak your plan, adding or cutting back on calories to see how your body responds. This is what a lot of people do throughout their journeys until they find the magic number that starts peeling away the pounds. It takes guessing, checking—and time. And it can work.
But there is another option: You can take a simple test to find out exactly how many calories you're burning each day. This eye-opening RMR test is non-invasive, takes a few minutes of time, and is pretty widely available for a fee. I recently tried it myself along with two SparkPeople employees, Jeff and Jaime, both of whom have been struggling to lose weight.
The test uses a device called the MedGem (similar RMR tests go by other names, such as "New Leaf").  According to Becky, "These hand-held indirect calorimetry devices can help provide another vital piece to solving their weight loss puzzle." You'll find these tests available in many health and fitness clubs, doctor offices, training facilities and weight-loss clinics. While some might offer tests as part of a weight-loss or training package, others offer the test on its own for a fee, which can range from as little as $50 to $100 or more.

Dawn Weatherwax, RD, CSSD, LD, ATC, CSCS, is a registered dietitian, athletic trainer and certified personal trainer who specializes in nutrition and fitness plans for both competitive and recreational athletes. She recently invited SparkPeople to check out her Sports Nutrition 2 Go facility in Liberty Township (just outside Cincinnati) to try the MedGem test, which normally costs $65 per person at her facility.
So How Does a MedGem Metabolism Test Work?
The MedGem is an easy-to-use, handheld device that accurately measures oxygen consumption (VO2) to determine resting metabolic rate (RMR)—the number of calories your body burns at rest. Knowing your RMR helps you understand your unique metabolism so you can develop a personalized plan to reach your goals.
The MedGem itself is basically a mouthpiece that you breathe into through your mouth while your nose is plugged. It takes about 10 minutes. It's neither uncomfortable nor difficult to do—you just sit still and breathe. The machine is hooked up to a computer that measures how much oxygen you use, which its software uses to determine your metabolic rate.

How to Get Accurate Metabolism Testing Results
When you prepare for an appointment, you have to follow this protocol for the most accurate reading:
  • Do not consume any food for 4 hours prior to your appointment.  
  • Do not consume any caffeinated beverages (i.e. coffee, soda, energy drinks, etc.) for 4 hours prior to your appointment.  Sipping on water is OK.
  • Do not perform any strenuous physical exercise (i.e., vigorous running, strength training, etc.) for 4-hours prior to your appointment.
  • Abstain from all tobacco products for 1 hour prior to your appointment.
  • Continue taking all prescribed medications as indicated.

We chose an early morning appointment to make it easiest to stick to these guidelines.

Our Results
Here's a chart of our results. I'm sharing our heights, weights (as taken that day), and ages as well so you can see how each of our metabolisms compare given those differences.
Name Age Height Weight RMR Result
Jaime (F) 35 5'5" 182 2,190 calories
Jeff (M) 42 5'6" 247 2,230 calories
Nicole (F) 29 5'8" 145 2,410 calories

I was particularly fascinated in how we all have very different body sizes yet our RMRs were within just a couple hundred calories of one another. I would have assumed that people who had more fat mass would have much slower metabolisms, and that would be one of the big reasons that they struggle with their weight. But at least as far as the three of us are concerned, we're all pretty close to one another, assuming we all got accurate results.

What I can say for sure is that all of us were pretty close in actual "lean" (non-fat) body mass, based on other tests we did that day. So regardless of how much fat each of us carries, Jaime and I, for example, were within 1 pound of each other in our lean mass, and Jeff had about 30 pounds more of lean mass than each of us. These results seem to make sense to me considering those other facts--but I'm no expert in this field of testing either.

So How Accurate Are These Results?
According to Becky, "Recent studies indicate that for 'healthy' adults, these hand-held, easy to use,  indirect calorimetry devices provide similar results when compared to the more expensive, and more cumbersome large cart equipment that also requires careful calibration and isn't widely available." Current studies are now investigating their accuracy with specialty populations such as older adults, children, hospital patients on vents, and the malnourished, she explains.

Of course, a person's activity level adds another level of calorie burning on top of this.  The more active you are throughout the day (taking the stairs, walking around, etc.) and the more you exercise—the higher your body's calorie needs will be.
So What Does This Mean for Weight Loss? How Do You Use This Information?
Having witnessed the results of more than 3,000 metabolic tests, Dawn has noticed quite a few trends. Her first step is comparing the result of test with the amount of calories a person actually eats. If a person is eating more than they burn, then the issue is clear: They are simply eating too much and need to cut back.
But more often than not, individuals who have been eating far less than their RMR but still aren't losing weight can mean one of two things, according to Dawn:
  1. They are actually eating far too little. She's seen it more times than she can count, both in overweight individuals and in people who only have another 5-10 pounds to lose. When a person consistenly eats too little, your metabolism can lower, mainly because you can't "give your all" to your daily life or your workouts. In these cases, she advises people to slowly increase their calorie intake by a hundred calories a week until they find that "sweet spot" where they have more energy, feel better, and allow their bodies to let go of some of its body fat.

    My co-worker Jaime thinks this may explain why she has struggled to lose weight even though she exercises five days a week and maintains a calorie-controlled diet. "I now understand why my body has not been losing fat as quickly as I had hoped despite all my efforts," she said after the test. "I essentially was not fueling my body enough (eating around 1,200 calories a day) for it to feel comfortable with letting go of fat! I’m now working on increasing my daily calories to 1,600 on non-workout days and just over 1,800 calories on the days I do exercise."
  2. There are underlying medical or hormonal issues interfering with their weight loss. Hormonal imbalances, such as low testosterone or thyroid issues, can affect your weight as well, says Dawn. "If a person is eating within an appropriate range for weight loss but is gaining weight or not losing weight, hormones may be to blame," she says. When the numbers simply don't add up, she advises that people get a full hormone profile at their doctor to see if anything is out of whack. Often, getting those hormones back into their healthy, normal ranges (via medical intervention) can be just the ticket to speed up weight loss. "Low testosterone is more common than you might think—in both men and women. So is a low-functioning thyroid," she explains.

    Jeff has been eating within a reasonable calorie range for weight loss without getting results—but he does have thyroid problems and realized he may need to check-in with his doctor and see about increasing his medication. "Since I have hypothyroidism, this will prove invaluable information to have while undergoing my other routine medical testing," says Jeff. "I think this is a great baseline for trying to kick-start my weight loss quest again. Knowing how many calories my body burns each day, and being able to use SparkPeople's free Fitness Tracker and Nutrition Tracker to calculate calories in and out should give me a great idea of how well I’m doing at burning calories and losing fat."

For the cost of the test, I think this is a worthwhile investment, especially if you've been on a long-term plateau or are truly doing "everything right" but not seeing progress. Most of these tests are administered by dietitians, fitness professionals, doctors and other wellness providers who are trained and capable at interpreting the results and offering valuable advice on how to use the results to reach your goals, although working directly with a licensed and/or registered dietitian would be ideal. To find a location near you that offers MedGem metabolism testing, click here.
"The whole experience was extremely valuable in helping me understand my caloric needs with the current condition of my body, but more importantly helped me 'reset' in my mind what I need to focus on moving forward," says Jaime.
Jeff had a great experience as well, both as a jump-start to get him focused on the right things to lose weight and to better understand how his body uses calories. "I was surprised to learn how many calories his body uses just standing still and not doing anything," he commented.
Thanks again to Dawn Weatherwax and Sports Nutrition 2 Go for letting us try the MedGem metabolism test! Stay tuned for a follow-up blog about another fun and interesting test we tried during our visit.
What do you think about the MedGem test? Would you try it? Have you ever had your metabolism tested?