I've used Lumen to hack my metabolism for a year — here's the results

a photo of the Lumen device with the Lumen app
(Image credit: Lumen)

When it comes to weight loss, or even just eating smarter, there are more diet plans out there than we can keep track of — and the trends seem to shift with the seasons. While many of these diets may be successful, when it comes to maintaining a healthy weight, the one thing that never holds up for the long haul is deprivation. 

That’s why personalized nutrition — which includes figuring out how your body responds to different types of foods and exercise — may be the dietary wave of the future in the same way personalized medicine is using genetics to determine appropriate individual medical interventions. 

If you extrapolate on the theory that food is medicine, then it makes sense to see what “side effects” your nutrition is having on your system. This is where some of the newest tech-tied nutritional developments can really be an asset. 

Enter Lumen, an at-home breathalyzer device that is advertised as a way to “hack” your metabolism by measuring your metabolic rate via the carbon dioxide (CO2) concentration of your breath. The concept has garnered a great deal of attention since we did a comprehensive review of the Lumen device last year. As a result, we decided to look again at the Lumen and further explore the reasons why this metabolic mouthpiece may (or may not) be a worthwhile addition to your personal dietary arsenal. 

a photo of the Lumen device with the Lumen app

(Image credit: Lumen)

I’ve been using the Lumen for a year: Here’s what I like

When it comes to nutritional assists, there are many upsides to the Lumen. To begin with, its creators — who are Ironman triathletes with PhDs in Physiology — have put a lot of thought into the product. This doesn’t seem to be something that’s being sold purely as a weight loss gimmick, but rather as a way to help people understand their bodies and metabolic processes better. And that focus on metabolic efficiency versus just pounds lost on a scale is a healthy way to approach eating.

In addition to that, here are some other things on the “like” list for Lumen.

It’s portable

To get a metabolic reading in the past, you had to go to a lab. Now you can keep your “test” in your purse or gym bag. Since the Lumen is about the size of a Twinkie snack cake (without any of the calories), it is easy to take it on the go. For individuals who really get in the swing of the program and want to record metabolic measurements throughout the course of the day to see how exercise/food/stress are affecting them, this is a major plus. 

Also, taking a moment to breathe into the Lumen instead of grabbing a nosh is a smart habit swap.

It allows for personalization

Back to the idea of personalized nutrition, Lumen also takes into account personal preferences and goals. This is a great feature since it allows you to go way beyond inputting simple basics like height and weight. 

For example, you get to select your eating preferences — meaning “Vegan” is an option as well as “I eat everything.” That personalization makes it such that when someone who follows a Vegan diet is given recipe suggestions, a sauteed steak won’t pop up as a recipe to try.

Also, a person can select different “tracks.” In other words, “Weight loss” may be one goal, but there are also options like “Fitness Performance” available. And in the latter category, you can break it down even further, choosing from a track set up for “building muscle” versus one for “improving body composition.” 

It’s helpful that along with recognizing not every metabolism is identical, Lumen realizes that not every user has “weight loss” as their dietary goal. 

It’s all natural

While many dietary programs require an additional investment in pricey meals or supplements, Lumen works with whatever you’ve got going on. This is an all-natural addition to your nutritional plan because you’re not required to ingest anything other than the foods you’re eating. There is a focus put on making smarter food choices (i.e. more protein, lower carbs, moderate fats), and encouraging users to eschew processed foods. But in general, the Lumen is an all-natural support tool in a compact tech package.

Basically, you don’t have to blow cash on extras here, you just have to blow air into a tube.

It’s educational

If you use Lumen the way the creators intended — that means also partaking in all the app has to offer including instructional videos, meal plans, and more — you will absolutely learn something about health, nutrition, and your own body. And that’s awesome!

The whole point of making changes to one’s dietary habits (and potentially metabolism) should be a heightened awareness that we really are what we eat. And what you put into your physical body will affect the energetic output that’s available to you (not to mention its appearance, if that’s your goal).

There is an extensive video library in the app for users, and when you do your morning measurement, there will also be a quick video you can watch called your “Daily Dose.” If you’re keen to learn, you should tune in to these, because education really is power when it comes to figuring out what best fuels your body. 

It’s got great support

Need help? Got a question? You can message a Lumen expert at any time on the app. They may not always be available that second  (i.e. in the middle of the night), but they’ll get back to you quickly. And knowing that you’re not in this dietary adventure alone can be of solace to many a Lumen user.

There is also a very complete “Help center” feature in the app that offers FAQs, assistance understanding Lumen levels, nutrition information, and more. All of this adds to the “education” category above and helps users make the most of their experience if they take the time to read these sections or watch the corresponding videos.

And for those who like a community, the Facebook group of other Lumeners is now at about 50,000 users. Meaning, you can find Lumen “friends” to be social with as well. 

It holds you accountable

Owning this device will make you think before you eat. The more you blow into it, the more you’ll wonder what will happen to your subsequent measurements if you eat those three cookies right before bed.

In other words, if mindless eating has been an issue for you, the Lumen can definitely work. You’ll start to feel like you have a little Lumen spy looking over your shoulder when you’re making your food choices. 

For people who need something to keep them on track with their healthy eating goals, Lumen can absolutely fill that void. Even if you’re sure you won’t care what it says, once you get into the habit of checking your levels, you’ll absolutely start to wonder “What will Lumen think?” Because no one wants to disappoint their new accountability partner, right?

a photo of a woman blowing into the Lumen

(Image credit: Lumen)

I’ve been using the Lumen for a year: Here’s what I dislike

For all the positive attributes of the Lumen, of course there is the flip side. Just like no two metabolisms are the same, not every program (or dietary plan) works for every individual. Here are some things to know about the Lumen that you may not gel with before you decide to try it out.

It feels overly focused on fat burning

For something that claims metabolic flexibility as the goal, there is just too much focus on more fat burning as the ultimate quest. While it is true that burning fat can be a great source of sustained energy and that for those who desire weight loss it’s better to burn it than store it, it’s not the only way to stay slim.

For individuals who are already fairly lean, it can get really discouraging to be told repeatedly by Lumen that you’re good at burning carbs, but not fat. It is possible that for some metabolisms, they are already doing a fairly decent job of burning fat and carbs in line with what they eat and how much exercise they get. And that’s true even if their CO2 measurements say otherwise.

In fact, the Mayo Clinic says that slow metabolisms are rarely the cause of weight gain (or an inability to lose weight). The standard equation of eating too much and not moving enough are more likely the culprits in most cases. 

It requires a detailed food log

If you’re not interested in counting your “macros” (a term they use a lot in the app meaning macronutrients), you’re not going to get the most out of your Lumen. 

Though the app doesn’t make you record calories, it does ask you to record how many carbs, fats, and proteins you eat daily. In grams. So unless you have a food scale and feel like measuring every single portion of food you eat, you’re probably going to be just guesstimating (for which it also gives you approximations of portion sizes). But this can become quite tedious. 

If you don’t record what you’re eating, however, then the Lumen can’t really maximize its suggestions to help you know how certain amounts or the timing/intake of different foods are affecting your metabolism. That’s because each morning after you breathe into the Lumen, you’ll be given a prescription for a low, medium, or high (though those are rare) carb day. And the more Lumen knows what you’re eating (as well as your CO2 level), the more it can personalize those daily prescriptions.

That being said, while some people need to keep a food diary to stay on track, for others it can lead to too much focus being put on every single morsel ingested (which can also be unhealthy, especially for people with disordered eating tendencies). 

It has a hefty up-front price tag

If you’re looking to try Lumen, you have to shell out a chunk of change right away. The smallest investment you can make at the start is $249 for the Lumen and a 6-month subscription to the app. While the price tag does make sense since you’re buying not only a high-tech breathalyzer but also access to the supporting nutritional program, you need to be sure you’re going to use it, or it’s not worth the cash. 

There is a 30-day money back guarantee, but since it takes weeks to get the first assessment of your metabolic flexibility (your “Flex Score”), that may not be enough time to truly know if this is working or not?

That being said, if it does feel like a good fit for you, the price amortized over the length of the subscription becomes much more accessible (especially if you sign up for a 12-month plan currently “on sale” for $299). 

It pairs with only select fitness trackers

While obviously this is a “bonus” feature — that is actually cool because it makes it easier and more accurate to add info like exercise levels and sleep into your Lumen readings as well — the Lumen only links with a few fitness trackers (i.e. Apple Health, Google Fit, or Garmin). 

If you’re using a different brand of tracker, you may start to feel incompatible with your Lumen since you’ll still have to enter all that info manually instead. While it’s not a deal breaker and we totally respect it would be impossible to pair with every tracker on the market without that becoming a full-time focus for Lumen, if you own a different brand, this is something to be aware of before you jump into Lumen-land. 

It holds you accountable

We’re also putting this one in the dislike category because a person can easily fall into a love/hate relationship with their Lumen. For those who need to be kept accountable for what they’re eating, Lumen can serve as a great diet partner. 

But for individuals who do better with less structure in their diets (i.e. a more intuitive approach to eating) the constant reminder that every single thing you put in your mouth may affect the reading you get the next morning is not the best. And that can make a person really start to hate it. 

It’s like a morning after breath-of-shame when Lumen lets you know you blew it by putting you in the “You’re burning mostly carbs” category. But did you really blow it? Or did you just have a day where you pushed your body to burn what you ate a little differently? 

While Lumen aims to keep their messaging positive, it’s hard not to feel like a failure when your reading is less than stellar. That being said, love it or hate it, the Lumen will make you think about what you’re putting into your body. And for that reason alone, it’s a tool that can make a difference in your metabolism. But it’s up to you if you need to measure your CO2 as the means to your dietary ends.

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Kimberly Dawn Neumann
Freelance writer

Kimberly Dawn Neumann is a multi-published writer whose work has appeared in such outlets as Forbes, Cosmopolitan, Fitness, Women’s Health, Prevention, Redbook, Real Simple and more. A Summa cum Laude graduate of the University of Maryland’s College of Journalism, she is also a life coach and fitness professional with certifications from the Coach Training Alliance, the American Council on Exercise, and Yoga Alliance. This NYC-based overachiever has also published two books and performed on Broadway. She meditates twice daily to keep everything in balance.