Lumen claims to ‘hack’ your metabolism. I tried it to find out.

It’s 9 a.m. and a small breathalyzer-like device called a Lumen — which looks sort of like a bulbous silicone vape — is about to tell me what I already know. I sleepily inhale through it, hold my breath for 10 seconds, then exhale back through the device and wait for the results to come in on the Lumen app. Yes, it’s confirmed: I overdid it on the tacos and wings last night.

Lumen is a new health product that officially launches Tuesday. Through the device and app, Lumen aims to give people more information about how they process food in order to achieve fitness and weight loss goals by “hacking” their metabolism. Each time you breathe into it, the device analyzes your breath, giving you a score on a scale of 1 to 5 to tell you whether your body is running on energy from your fat stores (the ideal “fat burning” 1 or 2 state), the carbohydrates you’ve consumed (a 4 or 5), or a combination of both (a 3). It follows with a recommended meal plan of approximately how many carb, fat, and protein servings you should be eating, with the ultimate goal of making your metabolism more efficient.

“Lumen comes to answer some very basic questions users have … how my body’s functioning, how the things that I did in the past few days affected me, and what should I do today, what should I eat in order to achieve my goals?” Michal Mor, one of Lumen’s co-founders, told Mashable.

Michal Mor and her twin sister Merav Mor are both Israeli physiology PhDs and triathletes who co-founded Lumen in 2016. Lumen ran an explosive IndieGoGo campaign in 2018, raising over $2.3 million with nearly 10,000 backers. Since then, the company has raised over $17 million in venture capital, according to , and has received for the innovation of bringing a test that’s usually done in a lab environment to a compact consumer device. It distributed its first orders to backers earlier this year, and begins shipping out orders of the product, which you can buy for $299 on Lumen’s website (that includes the device and app), Tuesday.

To actually understand Lumen, you need to know a bit about metabolism science, so bear with us for a sec. Measuring a person’s metabolism usually takes place in a lab, and is not typically something people do regularly — let alone daily. Surprisingly, the amount of oxygen you breathe in, and CO2 you exhale, can contain a lot of information about how you process food. When you go in for a metabolism assessment, one number you’ll get back is your Respiratory Exchange Ratio (RER), which is the amount of CO2 expelled divided by the amount of oxygen inhaled. This ratio reveals what kind of fuel a person is running on; lower ratio means fat, higher means carbs.

Lumen’s internal studies and a have found that Lumen’s measurements are “comparable” to an RER measurement taken by a traditional device. However, the experts Mashable consulted — two members of U.C. Davis’ Health Sports Medicine program — aren’t entirely convinced of its accuracy, or usefulness. The SFSU study concludes that “Lumen can be seen to be an effective instrument for monitoring relative, individual changes in metabolic responses (within-subject consistency), rather than a substitute for laboratory-grade RER measurements.” In other words, the Lumen scale is a relative score that can track change over time, but is not an analog for a measurement you’d take in a lab.

“Without knowing how that correlates, it’s difficult to judge their scientific standard,” Dr. Brandee Waite, the Director of Physical Medicine and Rehabilitation at U.C. Davis, said.

I’ve been trying out Lumen for the past two weeks and am intrigued, if not totally sold. It has certainly made me more mindful of how the amount of carbs I eat, and the late-night snacks I consume — Lumen recommends overnight fasts of around 12 hours — might be undermining my weight goals in more physiologically complex ways than just packing in extra calories. For example, a Sunday Chinese food binge could prevent me from going into fat-burn mode for days. However, the daily breathing in the morning, and at additional times depending on other information the app asks for, is a bit of a slog, and I’m not sure the information Lumen gives me is something I can’t pretty much intuit for myself.

“If the device is helping you figure things out, awesome,” Judd Van Sickle, the head of the UC Davis Sports Performance and Wellness program, who runs a metabolic measurement lab, told Mashable. “If not, it’s a lot of breathing.”

If the device is helping you figure things out, awesome.

Using my Lumen on day one started with an exciting unboxing. The actual Lumen device is sleek, friendly, and comfortable to hold, and the box greets you with a friendly “Hello, I’m Lumen.” My new pal! 

First off, I had to download the Lumen app, connect my device, and answer a series of questions about my health goals, physiology, and lifestyle. After a set-up day comes a “calibration day,” which is when the actual breathing fun begins. On calibration day, you breathe into the device multiple times at certain intervals after waking up and eating. This is how Lumen gets to know your lung capacity, and what the founders describe as your “baseline” for how you metabolize carbohydrates, since that differs from person to person.

After that, Lumen is supposed to become a daily part of your routine. For the past two weeks, my morning has gone like this: First thing, I roll out of bed and make coffee (duh). But before I drink that coffee, eat, or do much of anything at all, I bust out my Lumen. The app guides me through a couple “Lumen breaths,” which involve inhaling steadily into the device, holding my breath for 10 seconds, and exhaling steadily until a soothing circle on the screen disappears. The design of the whole experience is easy to understand and almost meditative in its own right. There are worse ways to start a day than taking some deep breaths.

Once I’ve breathed two to three times, Lumen gives me a “score” out of five. The ideal zone in the morning is a 1 or a 2 because it means my overnight fast successfully switched me into a fat-burning state. It’s OK — even good — to score higher after carb-heavy meals. However, if I score above a 1 or 2 in the morning despite an overnight fast, which naturally depletes the energy from carbs (called glycogen), that seems to mean I’m still burning the calories I’ve consumed the previous day. The morning after the tacos and wings? I scored a 4. Yikes. On the flip side, on the mornings I woke up with a 1 or a 2, I felt triumphant.

Based on my morning score, and the scores over the past few days, Lumen delivers a daily food plan. This isn’t a detailed menu, but rather a guide about whether you should be eating a low-carb, medium-carb, or high-carb diet that day. 

“We are not trying to recommend a specific food, [like] today eat chicken with rice and some vegetables,” Michal Mor said. “That’s not sustainable.” 

Instead, they want to empower users to make their own food choices, guided by the carb, fat, and protein serving parameters the plan suggests that day. The Lumen founders even promised me that on some days, Lumen would actually recommend I eat a high-carb diet. After three days of recommended low-carb diets (to which I thought, “duh”), I was amazed and, to be honest, THRILLED when Lumen suggested I have a “medium”-carb day. Lumen mixes in medium- and high-carb days when you’ve been in a fat-burning state for a while, to make sure your body doesn’t get too carb-starved and start squirreling away carbs when it gets them, instead of using them like it’s supposed to (this is a popular criticism of the keto diet, which attempts to cut out almost all carbs). 

I like that Lumen has education modules, presented sort of like social media stories, that taught me about metabolism, diet, and food. They were comprehensible and as easy to consume as delicious, delicious carbs — except they were about topics like how exercise affects your metabolism. While the main time to use Lumen is first thing in the morning, Lumen also encourages users to get their Lumen score before a workout, to help determine if they’re sufficiently fueled up. Then, 30 minutes after a workout, you can take your Lumen score again to see how running, weightlifting, or yoga affected your metabolism. Seeing my score decline after a hard workout was gratifying.

After one month of using Lumen, and in subsequent months, I’ll get what the company calls a “Flex score.” This is the long game of Lumen: to improve a person’s “metabolic flexibility,” which is how capable a person’s body is at switching between fuel sources at appropriate times. The daily plans of low-carb days with medium- and high-carb days in between are all in the service of working your metabolism’s agility.

“Metabolic flexibility is the main player that extends behind everything,” Michal Mor said. “Behind performance, weight loss, longevity, energy. So, we first want our user to achieve healthy metabolism, a flexible metabolism, and the outcome of that is weight-loss improvement.”

While some recent studies and experts endorse the general idea of metabolic flexibility, the “flex score” is a calculation of Lumen’s own creation based on the weeks of data users submit. There is not a scientific analog of the score.

“I like the idea of metabolic flexibility,” Van Sickle said. “What I see is that most people are metabolically inflexible in that they can’t use fat appropriately, because of too much glycemic load [carbohydrates] in their meal for their activity levels. So, if we have a tool to help guide us towards better fat utilization, that’s good.”

I haven’t received my flex score yet, but I can see how monthly attempts to improve it would be motivating.

And that’s how I’ve come to see Lumen, mostly: as another tool for motivation. I can’t say that I’ve stuck to its daily plans in order to truly hack my metabolism, but seeing numerically that my metabolism is working the way it’s supposed to — and working in overdrive when I house too many wings — was great feedback for how I treat my body. The Lumen founders agree that this is one of its main benefits.

“I think every diet, if you’re sticking to it and making sure that you’re eating healthy food — I mean real food — will work,” Merav Mor said. “The question is, how can you help everyone to stick to it? I think that [Lumen’s] feedback loop, once you see how the things that you did yesterday, how they help you and for how they affected you, will provide you with the motivation to keep to the healthy diet.”

I’ve come to see Lumen mostly as a tool for motivation.

While the promise of a consumer metabolism device is appealing, experts still have doubts about Lumen’s approach and some of the claims Lumen makes about its ability to “hack” your metabolism. Both Van Sickle and Waite of the UC Davis Physical Medicine department had a few main problems with Lumen.

First, they were not convinced of the device’s accuracy overall. And even after reviewing the scientific literature sent by Lumen, the way the scores track with RER was a source of confusion.

“Lumen’s home page says it’s been scientifically proven to meet the gold standard of metabolic measurement,” Van Sickle said. “But when you look on their ‘how it works’ page, it says Lumen exhibits ‘similar trends’ to the gold standard. So, that’s not the same thing.”

There were some bigger picture concerns, too. Waite explained that a person’s resting RER does not typically change day to day, so did not see the value in measuring it daily. She suggested that it’s a measurement you would typically take before and after, say, a month of trying a diet or fitness regime, to see how it’s affecting you.  It’s unclear how the fact that Lumen is a relative score — not an RER score — changes this assessment.

Additionally, Van Sickle was curious about the premise of the device as a whole: that you base a diet around your metabolic state in the first place, rather than the activities you’re going to be doing that day. He also questioned whether the goal of metabolic flexibility is really so well-reflected in a Lumen score. For example, if you eat a high-carb meal, but you’re not partaking in physical activity, the fact that your body is running primarily on carbs afterward is not necessarily a good thing for him. I explained to him that the morning after I ate a big, delicious cookie shortly before I went to bed, I got a “3” lumen score in the morning, despite having a low-carb day otherwise. 

“That’s where I get a little confused,” Van Sickle said. “So, they might say that’s a sign of good metabolic flexibility, when I would think of that as not necessarily good flexibility because your body doesn’t know what to do with that cookie. I’m not sure what the optimal case is.”

Overall, Van Sickle and Waite had too many questions about the scientific claims and assumptions Lumen makes about both its technology, and understanding of metabolism and diet, to be enthusiastic about it. However, both saw its value in helping people be more thoughtful about diet and exercise. (As always, seek advice from a doctor before starting any heath or diet plan.) 

“It’s definitely going to be making you more mindful about what you’re doing,” Van Sickle said. “Some of the underpinnings I’m not quite sold on. But big picture, as a mindfulness device, I don’t think it’s the worst thing you could do.” 

In the tech wellness landscape of devices that purport to help you by quantifying every aspect of your physiology, that larger assessment is all too common.

“Sometimes new technology, whether it really does what it says it does, if it gets people eating right and being more active, the side effect of having a more healthy approach to your lifestyle is a good thing,” Waite said.

Whether that “good thing” is worth a hefty price tag is up to you to decide.