There are many myths about weight loss, but there’s one that’s particularly persistent.
“Most of my patients coming in for medical weight-management tell me, ‘I have no metabolism.’ Obviously, that’s not true,” says Jody Dushay, an endocrinologist at the Beth Israel Deaconess Medical Center and assistant professor at Harvard Medical School. “Metabolism is literally the function of every single cell in your body.”
In order to function, your body converts food into energy. It’s a complex and personal process, determined by your age, gender, muscle-to-fat ratio, exercise levels, hormone function, and more. Dushay says that blaming a “slow” metabolism for weight gain (or crediting a “fast” metabolism for weight loss) isn’t medically accurate—though your metabolism might differ from someone else’s, the pace is determined by what your body needs.
You also can’t blame your sluggish metabolism for weight gain later in life; as you get older, you move less, and moving less means you’ll lose muscle and gain fat. Generally, people with “faster” metabolisms, for lack of a better word, need more calories to sustain basic functions such as breathing and blood circulation. But having a faster metabolism doesn’t necessarily mean you’ll have a leaner body. In fact, studies show that people with bigger bodies need more energy for basic functions, so they tend to burn calories at a faster rate.
Complexity aside, however, when there’s a connection to weight loss, there’s money to be made. Naturally, there is a company attempting to help its customers peer into their own metabolisms to better understand them, and, ultimately, tinker with them to boost their health.
In 2014, twin sisters Merav and Michal Mor, both Ironman winners with Ph.D.s in physiology, developed the Lumen: a vape-like device that measures metabolism and gives recommendations on what to eat in order to improve its functioning. Lumen, which went on sale in 2018, promises users everything from easier weight loss to better moods, boosted energy, improved sleep, and greater overall health. The $250 price tag includes the device and three months of access to its app, or you can pay $300 for six months or $350 for 12.
As an active 26-year-old with a general understanding of fitness and nutrition, the potential to “hack my metabolism,” as the company claims, intrigued me. After coming across several social media posts about the Lumen, most of which appear to be advertisements from the company’s influencer program, I decided to give the device a try—as well as call up experts to see if there is any validity to the brand’s claims.
Once I received my Lumen in the mail, I downloaded the app and answered questions about my age, weight, height, sleep routine, menstrual cycle, and goals (I selected “healthy weight loss” for journalism’s sake). It was then time for my first morning measurement. I had to inhale from the device for four seconds, hold my breath for 10, and exhale into it for six while keeping a ball inside a circle on my screen. It took me about eight dizzying attempts before the app accepted my breath sample (these tests got easier over time). Gas, temperature, and pressure sensors in the device measured my oxygen consumption and carbon dioxide production. The Lumen takes this information and tells you on a scale of 1 to 5 whether your body is currently burning more carbs or more fat.
My first “Lumen level” rang in at 2, meaning my body was burning more fats—a sign of a “healthy metabolism” in the mornings, after workouts, and “optimized fasting,” according to the app. Nonetheless, I was immediately advised to have a “low carb day,” which, according to Lumen, is the first step in the journey to improving metabolic flexibility, or how easily the body can switch back and forth between fats and carbs. The company says this flexibility is critical to weight loss “because you can lose weight, but still not train your body to use the food you eat properly”; it’s why many people who lose weight tend to gain it back later, the company says.
For nearly two weeks, I did as the app suggested, measuring my metabolism as soon as I woke up, again before going to sleep, 30 minutes before and after exercising, and one to two hours after eating. I followed meal suggestions from the app as well; they included simple but limited recipes, such as a corn-tortilla wrap with chicken salad or pork with grilled vegetables.
I wanted to enjoy the Lumen experience, but it just wasn’t practical or helpful in ways that differ from other health trackers I’ve used, like an Apple watch and a FitBit. Two weeks is a lot to spend breathing into a device at so many various intervals, but the Lumen app advises that users should do this over months for the most accurate results and advice. Although most wellness goals require similarly lengthy dedication, I wasn’t motivated to keep using the device because the advice I received didn’t differ enough from my normal routines and what I already understood to be a healthy lifestyle. For example, it’s no surprise that a late, indulgent dinner would be followed by a recommendation for a low-carb meal the next day. (Though I did appreciate that the Lumen’s diet recommendations were based on macronutrient grams—fats, carbs, protein—instead of calories, which can ensure that you’re not going hungry in your attempt to lose weight.)
What’s more, the fancy scores and data left me more confused than when I started. For example, my daily Lumen levels didn’t always shift to reflect what I ate, so I often didn’t know how to manipulate my behavior or meal choices to ensure my body was burning what it “should” at any point in time. After joining a company-run Facebook group with over 54,000 members called the Lumen Community, I learned I wasn’t the only confused “Lumener” out there. Many people in the community complain about not understanding their Lumen levels and their lack of progress (and even weight gain) despite following the app’s advice and taking advantage of its numerous explanatory videos and live-support chats with nutritionists. One member called the Lumen “Weight Watchers with a really expensive gadget.”
Chatting with experts, I learned why a device like the Lumen could be problematic.
It’s not that breathing into a device to get data on your metabolism is total hogwash (though you might be forgiven for thinking that at this point in the piece). Experts use breath to get a peek into what’s happening in the body all the time with some standard tests such as metabolic carts; as the Lumen does, they measure oxygen intake and carbon dioxide output in your breath, a metric called the respiratory exchange ratio. Because all cells need oxygen (aka energy) to function (aka your metabolism), this ratio tells us how the body is using energy; the higher it is, the more carbs you burn and vice versa.
But “a single breath is not informative,” Dushay says. Standard metabolic tests can be as simple as lying down for 30 minutes while breathing into a mask—much more time-consuming than a day’s worth of Lumen measurements—or as complex as living in an enclosed metabolic chamber for 24 hours. These tests are done in highly controlled settings, and people undergoing the test must have fasted and avoided exercise for at least eight hours prior. What’s more, they are expensive, and are rarely used outside of research studies, where they can assess the effects that a medication or diet might have on resting metabolic rates or total energy expenditure.
Whether the Lumen can compare to these testing methods is hard to say. While a 2021 peer-reviewed study that included 33 healthy adults found that the Lumen’s measurements were comparable to metabolic carts’, Dushay says she’s not impressed with the data or the scale of the study, which was conducted with the help of the company’s co-founder and head of research. Plus, Dushay says that daily Lumen levels are an example of “black box data,” as it’s unclear what information goes into its algorithms.
Perhaps the bigger question is: Can the Lumen’s metabolic assessments translate to meaningful personal diet recommendations that improve users’ health? After all, what matters most to users is not that the device can replace state-of-the-art clinical settings, but whether it can give a regular person enough insight to shift the needle on their weight or energy. Maybe I, and those who took to the Lumen Community to complain, just didn’t have great experiences.
But John Jakicic, a research professor in the division of physical activity and weight management at the University of Kansas Medical Center, said he also struggles to see how Lumen levels and flex scores may guide someone to change their eating behaviors in ways that differ from what might normally be recommended. Lumen claims to go beyond general healthy-eating tips to offer guidance on exactly what your body needs to perform its best. “They’re basically saying they already know precision nutrition, and that concerns me a little bit,” says Jakicic. “The NIH is only now funding studies in this area.”
Though science may eventually give us more insight into what we personally should eat, most people are probably fine just following general nutrition advice in the meantime. “If buying this device helps people to be more adherent to a healthy way of eating, that’s fine,” says Jakicic. “But the majority of people probably aren’t going to gain much from this. Will the device measure what it says it’s going to measure? Sure. Will it actually change people’s behaviors and cause them to have better outcomes? I think that jury is still out.”
Sometimes, more data is literally just … more data, says Dushay. “It’s not necessarily helpful. In fact, data can be a lot more confusing when there’s no good scientific rationale for how to use it.”
Ultimately, I’m not convinced that people who have the Lumen will be better off or more likely to achieve their goals than those without it. So, for me, the Lumen feels like another shiny product that will eventually collect dust in a drawer. Although I didn’t use the device long enough to fully reap its benefits, I don’t regret cutting my experience short; the time commitment wasn’t worth the weak science.
Our metabolisms, for the most part, don’t need coaxing—they just need us to provide quality fuel so they can do their thing. The answer to losing weight, becoming more fit, or enjoying better moods is consistency. A product can certainly help you achieve it, but I’d argue that you can do that for free.