Do Handheld, Single Breath Metabolic Analyzers Like Lumen Really Work?
Metabolic analyzers — small, handheld breathing devices that claim to measure your metabolism and fat burning capability with a single (or very few) breaths— have surged in popularity recently. But are they too good to be true? In this article, I separate myths from facts and explore if metabolic analysis is truly as easy and accessible as some clever marketing seems to promise.
Some basic background and facts….
Metabolic analysis and breath measurements offer an incredibly detailed insight into a person’s metabolic activity by looking at their oxygen consumption (VO2) and carbon dioxide production (VCO2). This is the gold standard method of measuring how many calories a person burns, including where those calories are coming from – fats or carbohydrates? By combining VO2 and VCO2, one can calculate the number of calories being burned as well as the ratio of participation of fats and carbohydrates using this formula: Kcal = 1440 x (3.94 x VO 2 + 1.11 X VC02).
Keep in mind though, that our bodies have an amazing ability to continually adjust the amount of fuel used for energy throughout our daily activities. Respiratory Exchange Ratio (RER) is a measure of this process, determining how much oxygen we consume and carbon dioxide we exhale as a ratio between 0.7 and 1. With RER at .70, all calories burned come from fat burning, while with RER at 1 it’s 100% carbohydrates being burned – no contribution from fats!
As shown below in Figure 2, throughout this entire 12 min resting (RMR) metabolic test, RER ranges from as low as 0.74 (81% fats, 19% carbs) to as high as 0.92 (27% fats, 73% carbs)! The graph not only illustrates the vast range of RER over a relatively short time period, but also shows the overall volatility of RER on a per breath basis.
This volatility, which is completely normal, is why clinical advice recommends taking an average of at least 1-2 minutes of sample breathing where variability is low and typically includes at least 20 – 30 breaths.
The balance of O2 and CO2 in your breath and your RER is also heavily influenced by how you breathe. For example, shifting from nose breathing to mouth breathing will artificially inflate the levels of CO2 in your breath. This rise in exhaled CO2 will raise RER and make it appear as if less fat is being burned. Changes in posture can also impact measured RER. Even subtle changes can contribute to an upset in the flow of air entering and exiting your lungs, resulting in unexpected variations when measuring RER.
The best advice for capturing the most accurate snapshot of your caloric requirements and fat and carbohydrate burn, is to be sure to keep breathing at a steady rate, while remaining still in one position for at least several minutes. Wearing a face mask that allows the collection of exhaled air from both the nose and the mouth (versus the mouth only) is an excellent way to guarantee that your beathing stays natural and consistent and you get the most accurate results possible.
Metabolic analysis is truly a powerful technique to reveal the nutritional and training regimen necessary for achieving a person’s fitness objectives as well as exposing potential barriers to those objectives. Unfortunately, a representative picture of a person’s metabolism doesn’t exist in a single breath. Making the single breath analysis situation even worse is the fact that taking samples through the mouth delivers artificially altered metabolic readings.
At the end of the day, conducting daily metabolic analyses is unnecessary, and in some cases counterproductive, because our metabolism naturally fluctuates too subtly to make it useful to track on a day-to-day basis.