Lumen - Metabolism Tracker Device

Lumen is the world’s first hand-held, portable device to measure metabolism accurately. And it claims to fame is that it is designed to “Hack our Metabolism.”

Lumen tracks your breath to determine if you are burning more fat or carbs. If you are burning fat, you are closer to your weight loss goals. If you are burning mostly carbs, well, you may have some work to do (maybe more physical activity) to get closer to your weight-loss goals.

Founders Michal and Merav Mor, twin sisters and PhDs in physiology and cell biology, were in the final year of their education when they began training for an Ironman competition. The Mors felt that their research could inform how they worked toward the grueling experience, which is comprised of a 2.4-mile swim, 112-mile bicycle ride and 26.22-mile run. “It takes you 12 to 15 hours,” Merav explains. “And in order to do that, you must use nutrition in order to support your workout and to improve your performance.”

Merav says they noticed “a huge gap between the basic science and the clinical practice, meaning the technology and the knowledge and the insights that you can find in the science world is amazing, but eventually, what you can really use on a daily basis to make smarter decisions is very limited.” Eight years ago the pair founded Lumen, with a mission “to close this gap, to bring the technology that is already being used in the scientific world to the consumer.”

The device syncs to an app that includes metabolic tracking, personalized nutrition plans, and research on several other resources to learn more about living a healthy lifestyle overall s you can lose weight for good.

Lumen also has daily insights that improve your metabolism by improving metabolic flexibility. Metabolic flexibility is your body’s ability to shift efficiently between using fats or carbs as a source of energy. And it’s scientifically proven to meet the gold standard of metabolism measurement (RER) in multiple validation studies.

In a hospital or clinic setting, metabolism is measured by the respiratory exchange ratio, or RER, which is the ratio between the amount of carbon dioxide produced in metabolism and the oxygen used. This measurement estimates if your body is using carbs or fat for energy. The Lumen has a "sensor and flow meter" in it that uses the data from the RER tests to get that measurement at home.

The device is generally easy to use, though it's sometimes difficult to get an accurate reading. The app (Android or iPhone) instructs you to inhale through the device until a colored ring pictured on the screen expands to meet the outer circle. If you go even a fraction of a second too long, you have to try again. After holding your breath for 10 seconds, you exhale through the device until the ring on the screen disappears. You have to keep your exhaling steady, to keep an additional onscreen ball in the middle of a bar (as pictured in the screenshot above). This is less prone to error, though you'll again have to start over if you blow out with too much force. The whole process is tough. I got so frustrated a few times that I had to set it down and take a break.

Once you succeed at breathing through the device two to three times this way, the app gives you a score of 1 to 5, which tells you if you're burning mostly fat (1-2) or mostly carbs (4-5); level 3 means you're in the middle. Levels 1 and 2—burning mostly fat—are ideal for the morning. But a 4 or a 5 in the morning, after at least eight hours of no eating, means your body is still trying to burn through what you ate the day before. The app also suggests you take a breath measurement before a workout, to make sure you have enough energy. This is helpful for the newbies among us, but if you're well versed in nutrition, regularly work out, and eat well, you probably already know how your body reacts to certain meals and don't need a device to tell you. Having a score made me think twice about what I was snacking on, even if no one but myself was seeing it. It was just enough of an incentive to make smarter choices, instead of, say, spending an entire day eating nothing but frozen tater tots and rice sides. (Please tell me I'm not the only one?) Based on your score, Lumen builds a day plan for you, with a suggestion of eating low-, medium-, or high-carb foods. This was especially helpful for me because it offers advice in a way that's easy to digest (pun intended). It doesn't recommend you start an intense diet or make you feel like you're starving yourself, as some diets do. The app offers many suggestions for each of your three meals—like grilled shrimp with broccoli, cauliflower, and walnuts for dinner—and you can customize them. For example, one of its breakfast suggestions is scrambled tofu, beans, and a green salad. When you click on the meal, it gives you alternatives for each ingredient that still offer the ideal grams of carbs, protein, and fat. Instead of beans, you can substitute hash brown patties (my favorite); instead of tofu, you can have two boiled eggs and one can of tuna. This is a plus for anyone who does not want to follow a one-size-fits-all plan or doesn't instinctively know a good substitution for a food item they don't have or don't like. These suggestions also make it more likely you're going to enjoy the meal you're eating and not consider it a frustrating concession to a diet. To further personalize, you can choose if you're a vegetarian (or vegan), mark if you have any allergies, or if you don't eat a certain type of food, like soy or pork, for example. It's nice to have everything in one place, so you don't have to go searching for your own interpretations of meals. In time, it would be nice to see a larger, revolving menu of meals. The app helped me better understand what goes into a properly balanced meal, so even when I don't eat what it suggests, I'm more aware of what a normal meal should look like.

The app's learning section is also particularly useful. It offers quick explanations on a range of health-related topics, from how to properly use the Lumen device to what exactly the correct serving of carbs really looks like. You click through short slides like someone's Instagram story. Because you're not using the actual device much more than a few minutes a day, the battery lasts a while. The site claims it will last two weeks on one breath measurement per day, but since you're supposed to do more breaths than that, expect to charge it weekly, which is still great. It has a dock connected via USB-C for charging. I've noticed that the battery level can fluctuate. One day it may sit at 25 percent and the next morning jump to 30 or 35 percent, so charge it early when it's getting low.

Lumen's goal is to help you "hack" your metabolism so that you're capable of "metabolic flexibility"—meaning your body can efficiently shift between using carbs and fats as fuel—which is a result of time-restricted eating like intermittent fasting, exercising, and "macronutrient manipulation," or the process of altering the amount of protein, carbs, and fat you consume. This flexibility, according to the Mors sisters, can improve your insulin sensitivity, which will help your body effectively burn fat more. It will also make your blood glucose levels more consistent, resulting in more energy and fewer cravings, and help you sleep better and strengthen your immune system.

You need to use the Lumen every day for at least a month to get your flex score (a big commitment), because it's determined by your daily morning measurements and measurements after high-carb meals. The score ranges from 0 to 21, and I got a 6.7, which means I have low flexibility. Basically, I have some work to do, which isn't surprising. Eating and living healthy is a new journey for me, but after using it for six weeks, I do feel equipped to continue eating right.

I hated the Lumen for a few weeks, but in time I've grown to like it. It was refreshing to get straightforward information on how my body was working and reacting to the food I was ingesting, instead of trying to decipher the pages and pages of information on the internet written for and by already well-versed health pros. I also highly appreciate that this is an alternative to weighing myself on a scale each day.


Metabolic health has been touted as one of this year’s wellness trends as we look to more scientific-backed methods to reach peak health. And with that, you should expect to come across the term ‘metabolic flexibility.

Metabolic flexibility is the body’s ability to efficiently switch between burning fats or carbs as fuel. The benefits of good metabolic flexibility include a stronger immune system, weight loss/maintenance, the ability to build lean muscle, and enhanced workout performance.

Until recently only elite athletes have been able to measure their metabolic flexibility in a lab. But now you can do it at home using a device you breathe into every morning.

According to the Lumen app, you need to use the device for 2 weeks to get your personalized Flex Score. So I wanted to try it out every day for at least that time.

During this time, I did the Lumen breath test device at times they recommended, which include:

  • When I first wake up

  • Before I work out

  • 30 minutes after I work out

  • After lunch

  • After dinner

I also tried to follow the low-carb diet nutrition guidelines recommended in the app. While I was not always successful with this, I tried my best to stick to the meal plan.

Alongside the breathing exercise, Lumen relies on user-submitted data points: the number of carb servings eaten the day before, how long breaks between meals lasted, the number of steps taken, workouts, how long users slept, and their current weight. All this data is considered and condensed to an assigned number from one to five, with one being burning fat exclusively and five being burning carbs only. Rather than a score or a grade, the assigned number provides a status update without praise or criticism.

With these numbers, Lumen guides users through the ups and downs of their metabolism—training them to burn fats some days and carbs others. This training ensures that even without the device, bodies will bounce back from more unhealthy days. It also debunks diets and alerts users when a current eating plan doesn’t seem to be working for their body.

“If you are on a low-carb diet for too long, you actually lose the ability to use carbs as legitimate fuel, which means that once you will eat carbs, your body will take those carbs and convert them to fat and store them as fat,” Michal adds. “In order to maintain your body’s ability to use both types of fuel, the app is, all the time, changing the personal ambition plan based on your own unique metabolism.” The personal ambition plan allows users to create their own goal: be it boosting energy, increasing muscle mass or losing weight. It also suggests daily nutrition plans and the adjacent app offers meal suggestions and recipes.

“The science is already there,” Merav says. “There’s an understanding that a healthy metabolism—a flexible metabolism—is actually the main player behind everything that you want to achieve. It’s not important if your goal is weight loss, athletic performance, or avoiding diabetes—all these are an outcome of a healthy metabolism. And, of course, this technology is not new. It’s something that’s already been used since the ’60s to measure metabolism. Athletes are using it all the time, people with diabetes use it in hospitals. It’s just that this technology has several disadvantages, and Lumen makes it all far easier.”

“The main questions our users have when they wake up in the morning are: ‘How is my body functioning? What did I do and the past two or three days that affected my metabolism? What should I do today? What should I eat?'” Michal tells us. “They want Lumen to tell them exactly the number of carbs and the amount of fat and protein they should receive. We provide our users a sense of control and the data to empower them to make smarter decisions.”


I’ve been using Lumen for just under two weeks and I’ve found the experience fascinating.

Firstly, let’s address its usability. The Lumen is a sleek little gadget that’s easy to navigate after a few practice rounds. You breathe into the mouthpiece, hold your breath for 10 seconds and then exhale, which sounds simple enough. However, exhale too quickly or too slowly and it’s not able to get an accurate reading.

You’re supposed to record your breath first thing in the morning, having fasted for at least 12 hours – not a problem if you eat your evening meal early enough.

Most days I’ve been waking up in a state of fat burn (a score of 1-2), which Lumen says is the goal. Largely, I think this is down to the fact I eat the bulk of my carbs earlier in the day thereby giving my body a longer window to metabolize them.


This brings me on nicely to my next observation regarding macros. Lumen provides you with a daily breakdown of carbs, protein, and fat based on that morning’s reading. The app doesn’t yet have a built-in food logging function, which is my only gripe, but you can use other apps like MyFitnessPal.

I found the nutritional advice especially helpful in terms of when to have a low-carb or a high-carb day (also called a ‘boost day’) to stay in fat-burn mode.

Lumen can also be used to indicate what eating (and drinking!) habits could be derailing your health and fitness goals. My most interesting reading of the fortnight was the one after a virtual Friday night vino party. I tracked a score of 5 the next morning, which means I was only burning carbs for energy (remember, 1-2 is the desired score).

The app explained this was because my body had been metabolizing the alcohol and then had shifted to using available carbs. Of course, confirming what I already knew – alcohol is the devil.


I’m yet to find out how flexy my metabolism is but I’m hopeful of a pretty decent score. My biggest takeaway from using Lumen is that I’m in tune with my body and fuelling it correctly (most of the time!).

My final thoughts? Throw away your bathroom scales because metabolic tracking is the future.

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