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?

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CHERYLHURT 3/19/2021
Thanks Report
LOSER05 1/10/2021
thanks Report
EVIE4NOW 1/10/2021
Interesting.. thanks. Report
BTINCHER2001 12/21/2020
I have had that test done twice, 5 years apart. The results were fairly consistent. I use RMR as a baseline for my caloric intake. ALL exercise I do is additional calories burned. I do get consistent weight loss. The balancing game starts when I go into maintenance! Report
RO2BENT 10/10/2020
It should get you close. I found mine empirically over time. Report
ROSSYFLOSSY 10/10/2020
Informative article. Report
DEE107 9/16/2020
thanks Report
Did that long time ago, back when I was counting calories and working out every day. The test said I could eat some 3000 calories a day and not gain weight. Less than that and I should loose wight. I was eating less than that amount and was not loosing. Report
Good need-to-know information. Knowledge is the power to make good choices! Report
Thanks! Report
I don't need to measure metabolism. It shows on the scale. Report
very interesting! Report
very interesting! Report
Very interesting! I have realised it more what I eat, rather than only the quantity that really affects me..... Report
Good to know info! Thanks! Report
very interesting. I would like to take this test and see what it tells me. I struggle all the time with my weight and this article has opened my eyes to a new possibility. Report
Thank you for the information. Report
good to know. wish i'd read when first started to see if it has increased Report
Sounds interesting Report
very interesting! Report
Interesting article. Report
Nice article and learning from it. Thank you for the article Report
Very informative. Thanks. Report
Thanks. Report
Thank you for an interesting article. Report
Interesting article Report
Thanks for sharing Report
Yes there is a lot more to losing weight than calories in, calories out. Report
good article Report
Yes, I've had my metabolism measured a couple of times. And I'm one of those who was eating too few calories, and messing up my results. I went to Kaiser's Member Education center to sign up for the test which costs $50 for a Kaiser member. Report
Interesting information. Report
Interesting article Report
Sounds like a useful tool to have when planning a weight-loss or maintenance diet. I think I'll look into it after I've achieved my target weight. I have to say, though, that I would DEFINITELY gain weight if I ate that many calories. I am 5'9"and USED to weigh between 135-140. Eating that many calories (over 2,000/day -- I know because I tracked it) is what caused me to GAIN 80 lbs. over the decade. Since I am not experiencing ANY difficulty losing that weight despite being in menopause, I have to assume that there is NOTHING wrong with my hormones. Report
Interesting Article about metabolism! Report
I haven't had my metabolism checked, but I do have thyroid problems. Am on medication for hypothyroidism. May have to check with my doctor about med adjustment.. Report
My situation was similar to BTINCHER2001. I was eating within my SP range and not losing, I was GAINING! If I stayed at the low end, I would maintain. I was getting extremely frustrated. I had my hormones checked, and the were fine. I contacted the weight management program affiliated with the hospital I work for, and they did the MedGem. My RMR was 300 kcals BELOW my minimum! I have been slowly losing since readjusting my calories. (15 lbs down since late October) Report
never had it done but may ask Dr when i go back in August Report
I had this done at Kaiser (fee $50, in the Education dept). I found out that my SP calorie range was too high. The minimum value was at my Base Metabolism Rate. So although I was eating the minimum allowed by SP, that was a maintenance level for my body. I have to adjust the SP calorie/fat/protein goals down for me. I'm down 62 pounds, and still losing. It works for me! Report
My RMR is measured at 15% below average at 1400 kcal. I did it twice with a space of five years and got almost the same results (I'm lower now). It sucks. Report
Okay, so when the article suggests adding "100 calories per week" I assume this means "add 100 calories per day for a week before making further changes." Can anyone confirm/deny? Report
This is great info but for those who don't want/can't afford to go through testing just search for a metabolic rate calculator online. I was working out and staying around 800 calories a day and had not been lossing weight for months. I was not hungry and was eating healthy but the calculator said I should be eating at least 1200 calories. I up my intake of things such as nuts to get to the 1200 minimum and I have been steadily lossing. 2 pounds this week! Report
Best article on SP and one I will take to my first one on one with an RD scheduled for mid January. And I will also have this discussion with my Chiro and md who was a physiotherapist previously. This comprises my team of experts yet I have not heard of this test. I am committed to tracking as accurately as possible with some success but struggle with injury and new limitations in the gym. And there is that inevitable age component and for most active seniors the notion that eating less is the only way to go.
This information has sparked me ... Power to the Spark People.

I always think it's funny when things say "abstain from smoking for 1 hour" or any period of time. If I could do that when I was a smoker, I wouldn't have been a smoker. How stupid.

It doesn't really explain why oxygen input would reveal your metabolism. I would think that lots of things could impact your oxygen levels.

I think that it would be simpler to just try eating at different calorie levels until you find one that works for you. Report
The ADA published research last fall reporting that the MedGem "significantly overestimates REE in middle aged, overweight, and obese individuals." They recommend using the traditional devices (where you breathe into a hose and all the oxygen is collected in the device for analysis) rather than the hand held ones. (J Acad Nutr & Diet 2013 Sept 16). It really is valuable information, but only if it is accurate. I'd find a doctor or trainer using good equipment before I'd pay money for a test. Report
When they say this test works for "healthy" individuals, what besides hormone and thyroid imbalances would throw the test off? The minute I saw that mask you have to breathe into, I worried that my asthma would cause problems with the results. Report
I have done a test at my gym with my trainer, and I burn about 1800 calories a day. This was super helpful for me, as I had been following a 1600 calorie per day plan, since I workout about 5 days per week. Well when my weightloss stalled , I recently tried a different way of eating, Paleo, but stayed within my calorie range, but am around 1300-1400 calories per day. Now the weight is flying off, for me it is a matter of listening to your body, not your head. That being said knowing my DCN (Daily Caloric Needs) helped me to see why/what wasn't working.

If you can find this test, do it, I feel the information is invaluable. Report
It sounds hopeful and beneficial to try to find out what we need to continue. I am sure that for many of us the hormones may be the culprit, although the calorie intake is quite a subject within itself because of all the myths about dieting. And its starting to sink in just how harmful those myths can be. I would definitely look forward to get GEM Tested... wonder what the cost would be. It must be very beneficial by far!! Report
I can only WISH that my body would burn 2400 calories a day just by breathing! I can't even burn that many when I work out strenuously. The most I have ever burned using a GoWearFit and walking at least 12 miles all around Rome one day was 2000. When I got my fitbit last year, I was incredibly disappointed that it indicated my gowearfit wasn't at all accurate! Now it takes a strenuous one-hour workout and constant activity all day to burn 1,700 calories. Clearly, we are all not created equal! If I ate what the sparkpeople website says I should eat, I'd gain weight. There's no two ways about it. So I am limiting myself to 1100 calories or under each day and consistently burning between 1500 and 1600 calories per day. I wish it were different. :( Report
This proves that we live in a cookie cutter world where everyone is expected to be the same. Thank God some people are challenging that notion and realizing God created us equal yet different.