Our Verdict
Lumen is a flow meter device that uses carbon dioxide (CO2) sensors to measure the carbon dioxide levels in one’s breath—an assessment of metabolic efficiency. Although relatively new on the market, Lumen’s handheld device, combined with the accompanying app, is a unique tool for metabolism tracking and overall health management.
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Lumen Metabolism Tracker
- World’s first hand-held, portable device to accurately measure metabolism
- Scientifically proven to meet the gold standard of metabolism measurement (RER)
- See how your metabolism is affected by your nutrition, physical activity and sleep
- Achieve sustainable weight loss with daily personalized meal plans
- $299 plus $19/mo, includes one free month of membership
Key Features
- Lumen’s device measures the body’s fuel source (carbohydrates or fats) in real time by analyzing the amount of carbon dioxide in one’s breath so users can make informed nutrition choices based on their unique metabolic needs.
- The companion app helps users track their meals and provides a detailed, individualized macronutrient analysis to promote better nutrition decisions.
- Lumen’s personalized nutrition plans update each morning based on the user’s metabolic data at that time.
Lumen was founded in 2014 by twin sisters Michal Mor and Merav Mor, both of whom have doctoral degrees—Michal in physiology and Merav in cardiac science. While training for an Ironman Triathlon, they realized the most challenging part of intense physical exercise is understanding one’s individual metabolism to give the body the correct nutrition for optimal performance. Today, Lumen is an at-home metabolic tracker that provides actionable insights into one’s unique metabolic needs.
Lumen uses patented algorithms, CO2 sensors, flow meters and other sensing technology to determine the carbon dioxide concentration in one’s breath, according to its founders.
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Lumen at a Glance
- Cost: The device costs $299 plus $19 per month for a subscription to the Lumen app.
- Design: The handheld Lumen device is lightweight and ergonomic with Bluetooth capability for connecting to the smartphone app.
- Health insights: The app displays your metabolism Flex Score, which shows your body’s flexibility at shifting between utilizing fats and carbs for energy, and individualized macronutrient goals and breakdowns based on one’s logged food intake.
How Lumen Works
Lumen is a health technology tool that provides real-time metabolism measurements. The small handheld device links to a smartphone app to provide insights into a user’s metabolism based on the concentration of carbon dioxide in their breath—an indicator of metabolic fuel usage.
After the user takes a breath test with the Lumen device, the app immediately displays their Lumen Level, a score that indicates whether the body is currently using fats or carbohydrates for energy. The goal is to have a balanced metabolism that can efficiently shift between using both types of fuel for energy, which is referred to as metabolic flexibility. Metabolic flexibility supports weight loss and maintenance because the body learns to burn fat as its primary fuel source. Based on data collected each morning, Lumen creates personalized daily nutrition plans for users.
The app also allows users to log meals and view the macronutrient breakdown of what they’re eating to aid in more balanced nutrition decisions. Individuals can also check their recommended macronutrient intake and track these levels throughout the day to get a better idea of how their meals impact their metabolism.
How Much Does Lumen Cost?
The initial investment includes the Lumen device, which costs $299 and ships free. After one purchases the device, a recurring subscription fee of $19 per month unlocks the Lumen app’s comprehensive features, including meal tracking, detailed macronutrient analyses and personalized daily nutrition plans.
Customers can use the Lumen device and app for real-time metabolic measurements, including their Lumen Level and Flex Score, without the monthly plan. However, some of the app’s other features like personalized nutrition insights aren’t available to non-subscribers.
If an individual isn’t satisfied with their Lumen device or experience, the company offers a 30-day money-back guarantee.
Lumen’s pricing is transparent with no hidden costs, though the monthly fee disclosure on the product page is relatively small compared to the surrounding text. Getting the most out of Lumen may also require a commitment to healthier eating and investing in more nutritious food choices, which presents a potential added cost.
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Take control of your health with Lumen and effectively monitor your metabolism, boost fat-burning capabilities and achieve sustainable weight loss.
The Lumen Product
The Lumen device fits comfortably in the palm of the hand and is designed to be held up to the mouth for breath measurements. It’s lightweight and easy to transport as well.
The device pairs with Lumen’s app on both iOS and Android devices. To get started, simply open the app on a phone with an active Bluetooth connection and follow the prompts to take a breath measurement. During my morning check-in, the device automatically logs it as such. However, there are other logging options, such as “before eating,” “after eating” and “custom.”
After choosing a log type, the device is ready to use. The app prompts the user to turn on the Lumen device by pressing the power button. Next, they’re prompted to inhale deeply for four seconds until the purple ball on the smartphone screen (which turns green upon inhalation) reaches the center of the target zone. If a user manages to keep the ball in the center for the entire countdown, the app prompts the user to hold their breath for 10 seconds before exhaling into the device. If one fails to inhale or exhale correctly (the ball drops out of the target zone for more than 1 second), a pop-up with a countdown will display with tips on how to measure properly.
Once a measurement is complete, the app displays the user’s Lumen Level, which indicates whether they’re using fats or carbohydrates for energy. The Lumen Level ranges from one to five:
- Level one indicates burning fat for energy
- Level two indicates burning mostly fat for energy
- Level three indicates burning a combination of fat and carbohydrates for energy
- Level four indicates burning mostly carbohydrates for energy
- Level five indicates burning carbohydrates for energy
After 15 days of consecutive testing, the app displays a second critical measurement called the Flex score, which indicates the user’s metabolic flexibility, or how well their body adapts to different fuel sources.
The Flex Score can be used in conjunction with the Lumen Level to gain an even more comprehensive understanding of one’s metabolism. After the initial 15-day test period, the Flex score updates weekly so users can track progress regularly.
Lumen also tracks and updates a user’s nutrition plan daily. The app provides a detailed analysis of one’s macronutrient intake and can even provide suggestions for healthier food options. However, Lumen users must log all meals and snacks to get the most out of this feature. One’s dietary choices, daily Lumen Level and the time they stop eating at night all influence the nutrition recommendations they receive from Lumen.
The Fine Print
While Lumen offers a uniquely scientific approach to nutrition, it’s not a magic solution for weight loss or health improvement. The device should be used alongside consistent healthy lifestyle choices, including balanced nutrition and regular exercise. Additionally, from a user’s standpoint, the device requires a solid commitment to logging meals daily, which can be time consuming for many and triggering for someone with a history of disordered eating.
The smartphone dependency may also pose a challenge. A user can’t perform measurements without their phone present.
The Lumen device is a tool for understanding one’s metabolic health and not a substitute for medical advice or treatment for specific health conditions. As with any health technology, it’s a good idea to consult with a health care provider before making any significant changes to one’s lifestyle or diet based on the data provided by Lumen.
What Experts Say About Lumen
Companies like Lumen help people—especially alongside a trained health care provider or health coach—leverage metabolic data to personalize daily habits for improved well-being, says Shilpa P. Saxena, M.D., a board-certified physician at Forum Health, a functional medicine clinic in Tampa, Florida. Understanding how one’s metabolism shifts throughout the day and over time can help individuals optimize their nutrition and lifestyle habits.
“The Lumen metabolic tracker was designed to provide users an at-home option for measuring their respiratory exchange ratio (RER), a measure of metabolic flexibility,” says Dr. Saxena. “Metabolic flexibility is simply the degree to which the body can flip between its ability to ‘burn’ fats or carbohydrates as fuel for energy and healing.”
According to Dr. Saxena, research suggests the tracker is accurate compared to laboratory measurements. A 2021 study in the Interactive Journal of Medical Research compared Lumen’s accuracy to the gold standard (metabolic cart) for measuring RER in a laboratory setting. The metabolic cart is a clinical test measuring oxygen use and carbon dioxide production for estimating an individual’s metabolism at cellular levels. The study found the device accurately captured RERs aligned with the metabolic cart[1]Lorenz KA, Yeshurun S, Aziz R, et al. A Handheld Metabolic Device (Lumen) to Measure Fuel Utilization in Healthy Young Adults: Device Validation Study. Interactive Journal of Medical Research. 2021;10(2):17. .
Dr. Saxena also says the app can help users understand how stressors, poor sleep or physical inactivity affect their scores. However, she warns that this information “is just information” unless one takes steps to make changes based on the data.
“Coupling your Lumen experience with a lifestyle medicine coach can help you make sense of all the information and recommendations so you can maximize success with the device regardless of what your goals may be,” she concludes.
The Lumen Experience
I ordered Lumen to better understand how my body converts food into energy. I received my device within five days of placing the order. Setting up the device and app is straightforward, and the user interface is sleek and easy to navigate. I downloaded the Lumen app and logged in using my email address, and I watched a short tutorial video that taught me how to use the device and app.
I was ready to start tracking once I connected my device to the app via Bluetooth. It took me a week to learn how to breathe correctly and maintain the ball in the target zone during readings. If I don’t do it correctly, the app has me start over after taking a small break. I think my asthma made it more difficult to follow the proper breathing technique at first, as I’ve always struggled with holding my breath after filling my lungs to capacity.
Each morning I wake up and use the app to measure my Lumen Level. My very first Flex score was four, meaning I was mostly burning carbohydrates for energy. Throughout the next two weeks, my morning Lumen Level ranged from one to five, indicating my body could (at least partially) switch between burning fats and carbohydrates for energy.
After 15 days of measurements, the app displayed my first Flex score of 12.3, indicating medium flexibility. I wasn’t surprised by my score, as my Lumen Level had mostly ranged from two to four during that time. The app uses a chart to plot my Flex score over time, so I can easily track my progress and see how different lifestyle changes affect my body’s overall metabolism flexibility.
The app also updates my nutrition daily. Depending on your Lumen Level and other factors, the app suggests a carbohydrate consumption amount for that day. There are low, medium, and high-carbohydrate options, which the app adjusts according to your results. For example, if you logged a high-carbohydrate day on Monday and your Tuesday morning Lumen Level shows you’re burning carbohydrates, the app may recommend a low-carbohydrate option for Tuesday’s meals. It’s all part of an algorithm I don’t completely understand, but I notice a correlation between my morning Lumen Level and the carbohydrate recommendations I receive from the app.
After the app displays my recommended carbohydrate level, I go into the nutrition section to see a suggested breakdown of carbohydrates, proteins and fats and a total calorie count for the day. This section also has helpful meal ideas with macronutrient and calorie information. Breakfast, lunch, dinner and snack options (around six to 12 recipes for each meal) are updated daily.
Although I haven’t been using the device long enough to see any significant changes in my metabolism, I’m already feeling more informed about the relationship between my diet and lifestyle. With each test, my Lumen Level is slowly dropping. I’m paying attention to how different activities and foods affect my levels each morning and how I feel throughout the day.
One of the biggest downfalls of the Lumen device is that it only works with smartphones. I don’t always have my phone with me in the morning, so there have been a few instances where I couldn’t use my device when needed. The ongoing membership fee may also be a downside for some; however, the additional expense is worth it if you’re committed to tracking your metabolism regularly and following the app’s nutrition plan.
Overall, I’ve already learned a lot about my body’s metabolic flexibility, including how diet and lifestyle choices affect it. I’m looking forward to seeing how my results change over time.
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Lumen's metabolism tracker can help you monitor and improve your metabolic health by helping you learn exactly what your body is using for fuel, fats or carbs.
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