Metabolic Testing Can Help You Lose Weight *If* You Know How To Interpret Your Results
Do you have that one friend who can eat whatever she wants without gaining weight? Maybe she credits a speedy metabolism for her ability to chow down on fries and never feel like her favorite pants are feeling the tiniest big snug. Meanwhile, you’ve been trying to eat nutritiously for months and still can’t seem move the numbers on the scale. Been there.
Here's the thing: It's actually possible that your metabolism is just different, (meaning, slower) than your friend’s. In case you’ve forgotten from your high school biology class, metabolism is the rate at which your body burns calories for energy. And it’s a complicated process that also involves your oxygen intake and carbon dioxide output (a.k.a. your breathing), the Mayo Clinic explains.
Everyone's metabolism is different, and those differences are generally based on height and weight, your activity levels, and the biggie, genetics. But knowing how your metabolism operates could be the key to losing weight more successfully—although getting deets on your metabolism is not as simple as, say, taking your temperature or timing how fast you can run a mile on a treadmill.
Understanding how your metabolism works requires specific kinds of testing, as well as a qualified professional to interpret those results and translate them into a customized weight-loss program. Interested in learning more? Here's all the info from experts on what various types of metabolic testing involve, plus who should be getting tested.
First: What does a metabolic test reveal exactly?
Metabolic testing measures how many calories a person burns while at rest (also called resting metabolic rate, or RMR), according to the Center For Metabolic and Weight Loss Surgery at Columbia University.
RMR tells you what your basic daily caloric needs are for maintaining your weight if you sit around doing nothing all day. Knowing that rate paves the way to more accurately calculating how many calories you would need to consume per day to lose weight.
In other words, if you’re dieting constantly but not getting the results you’re hoping for, metabolic testing could help you understand your body better and lead to more weight loss.
“A metabolic test can be very helpful for weight-loss goals because it is a fairly accurate way to know how many calories you need [to lose weight] while still allowing your body to function properly,” says Joanne Donoghue, PhD, exercise physiologist and associate professor at NYIT College of Osteopathic Medicine.
Striking that just-right caloric balance is important, says Donoghue. On a very basic level: Consume more calories than your body requires at rest and you gain weight; too few calories, and your body may slow down its metabolism in order to conserve energy, which can also lead to weight gain.
If your metabolism seems like one big mystery, that’s because it typically is for the average adult who hasn't done a metabolic test. But a metabolic test gives you actual numbers to work with so you aren’t just guessing at your caloric needs.
What are the different types of metabolic tests out there?
There are a few different ways to approach metabolic testing, but not all of them are the best choice—or even available—for the average person. These are the most common metabolic tests and what they involve:
Direct calorimetry: This measures your body heat to determine the number of calories you burn. Typically, you would sit inside a special chamber for about an hour while the machine does its thing. It’s basically considered the gold standard for RMR testing in terms of accuracy—but it’s so expensive and high-tech that it’s very rarely used outside of a research or laboratory setting.
Indirect calorimetry: This measures how much oxygen you consume compared with the amount of carbon dioxide you breathe out. It’s more portable, affordable and accessible than its counterpart, meaning this is likely the option you’ll be given if you’re signing up for testing through your gym. You simply wear a mask or lie down under a hood while a machine takes your oxygen and carbon dioxide measurements for about 15 to 20 minutes. Even though it’s lower-tech, Donoghue says it’s still pretty accurate.
VO2 max test: If you are an athlete who wants to optimize caloric intake or lose weight, you may also benefit from something called a VO2 max test, which measures your body’s ability to consume oxygen. For this test, you wear a breathing mask while running on a treadmill to determine how much oxygen you consume when you’re running at your hardest. It’s one of the most accurate tests for cardiorespiratory fitness, according to the University of Virginia School of Medicine.
If you’re not an athlete, you should probably stick with just testing your RMR using one of the first two options.
How accurate is metabolic testing?
In general, metabolic testing via indirect calorimetry is a reliable way to obtain information about your body that you might not otherwise have. But it’s also important to remember that a lot of the testing accuracy comes down to the equipment being used and who’s doing the testing and interpreting the results—more on that in just a sec.
Be wary of body composition tests that claim to predict your RMR and stick with indirect calorimetry, when possible. “There are body composition tests like hand-held dynamometers or scales that try to predict RMR, [but those] are prediction values and some more accurate than others,” Donoghue explains. “Indirect calorimetry, when done correctly, has the least amount of error."
A 2017 review of data in the Indian Journal of Endocrinology and Metabolism concluded that while predictive methods of testing are “questionable,” indirect calorimetry is a valuable resource for calculating nutrition needs and managing chronic health conditions.
If I want to get my metabolism tested, where can I do it? How much does it cost?
Originally, getting a metabolic test was a pretty exclusive thing, offered only at hospitals and weight-loss clinics. Now, it’s much more accessible, with many gyms and fitness centers, sports medicine facilities, and dietitian offices offering the testing.
Of course, that’s a “buyer beware” situation. Private- or corporate-owned facilities, like your local health club, may not be using the most accurate equipment (or keeping it running smoothly). Don’t be afraid to ask questions about the equipment being used and the professional guiding you through the test. Ideally, it should be a certified personal trainer, registered dietitian, or an exercise physiologist.
As far as the expense goes, Donoghue says a typical price range is $75 to $100.
Anything I need to know before going in for a metabolic test?
There’s not much you need to do to prepare—except fast the morning of your test, and not just from food.
“Restrain from having any caffeine, alcohol, or nicotine—and don’t exercise,” advises Donoghue. “If you’re tested within a few hours of any of these, the accuracy of your test will be greatly affected.” Beyond that, because it’s your resting metabolic rate that’s being tested here, there’s no pressure on you to do much of anything (basically, you get to chill).
One final thing: Remember that your results are just numbers, and without a plan in place to do something based on those numbers, it won’t change your weight-loss results.
The bottom line: Metabolic testing can definitely give you insight into how many calories your body burns at rest and how to create a calorie deficit. But shelling out for a metabolic test is only step one; step two is working with a personal trainer or registered dietitian to create a personalized caloric goal and fitness routine for weight loss.
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