Lumen review: get a unique insight into your body & how to properly fuel it





Ease of use




Value for money



  • Pocket sized, premium feel about it
  • Unique in what it does
  • See the results of diet & nutrition quickly
  • App has a wealth of data
  • Two week battery life


  • Requires lots of commitment
  • Monthly subscription

Smart scales are nothing new. Step on one of these, and your weight data will magically find its way to a corresponding app on your mobile device or web dashboard. You can then track your progress over time. But we are into 2022 and that’s not nearly enough. In this review I look at Lumen – a unique pocket-sized breath analyzer that wants to reinvent weight management by monitoring your metabolism and providing a customized nutrition plan. And it does all this by measuring the level of carbon dioxide (CO2) in your breath.

We first covered the gadget when it was launched back in 2018 via Indiegogo. An impressive $2.4 million was raised at the time from around 10,000 backers. After suffering a few delays in manufacturing Lumen is now available to all.

You might think your metabolism is the same each day, but this couldn’t be further from the truth. It all depends on what and when you eat, how much you exercise, how much you sleep and other factors.

Our bodies tap into two main sources of energy: carbohydrates and fat. Knowing the ratio at which these two are being used at any point in time is important to achieving your health, weight and exercise goals.

You want to wake up in fat burning mode and shift more into carb burning during the day. In fact, the more flexible your metabolism, the better. This is because it is a good thing to be able to shift quickly between fuel sources. A flexible metabolism is, for example, better at burning fat. Which makes shedding those extra pounds a bit easier. But Lumen goes further. It also tells you what and when to eat. This is a very unique device – unlike anything else out there.

All of this sounds great on paper but does this thing really work? Read on to find out what I made of Lumen.

Jump to

Design & hardware
Making sense of the data
The verdict, is Lumen worth buying?

Lumen breath analyzer review: Design & hardware

  • Premium feel about it – looks a bit like a vaping device
  • Small and lightweight – easy to carry around
  • Inside is a CO2 sensor and a flow meter
  • It only needs charging once every two weeks

Look & feel

Lumen has a very premium look and feel about it. The protective matte coating and removable magnetic cap contribute to this smart appearance. In a sense it reminds a bit of a vaporizer. Some will like that, others may not.

The build is sleek and compact and you can slip it into a little black travel pouch that comes with the purchase. It is very portable so easy to carry around in your pocket, bag or rucksack. Inside the box is also a circular magnetic charging dock and a detacheable cable that plugs into a USB outlet.

Lumen device next to travel pouch, charging cradle & charging cable

In the middle of Lumen is a circular LED with light shining from the inside when switched on. Different colours mean different things. Green, for example, indicates the device is charged while purple shows that Lumen is connected to your smartphone.

The power controls can be found below the LED. It is a single physical button that blends nicely into the body. A lot of attention was clearly put into detail as everything looks very slick and expensive.

The top of device is the part you are meant to rest against your lips and draw breath from. There’s a small split which serves as a mouthpiece. At the opposite end is the air exhaust.

This is a very personal device so I wouldn’t suggest sharing it with anyone. During use there will be a built-up in saliva. So you should clean it regularly. Having said that, technically you could let other family members use it. They can set up the app with their profile on their personal smartphone and link up to the same device.

The case is moulded of a single piece of soft touch plastic. The mouthpiece and cover are a bit heavier as they are made of stainless steel.

If you are wondering, the actual dimensions of the thing are 102 x 41.5 x 33.3mm and weight is 95 grams. The docking station measures 14.6mm x 76.4mm x 68.3mm and weighs 80 grams. It seems to be constructed of the same material as the body.

Under the hood

Inside of Lumen is where the magic happens. The company has patented technology that is able to do what is traditionally done via a metabolic cart or chamber. But this takes up to 60 minutes and is very pricey so available only to a select few. It is the type of technology used in labs.

Lumen review
Top split serves as a mouthpiece

Lumen has managed to squeeze a tiny CO2 sensor inside the device, along with a flow meter. These are utilized to determine the CO2 concentration in your body as you inhale, hold your breath, and then exhale. The algorithms sift through the info to figure out what fuel your body is using for energy (metabolic fuel usage) at that particular time. And this is done with just 10 seconds of use.

As mentioned, the fuel source can be carbohydrates, fat or something in-between. High CO2 levels in your breath are an indicator of the first, low CO2 levels of the second. At times it will be a combination of the two. And that’s the extent of the science lesson. Burning fuels from carbs releases more CO2 than from fat. With each use, the metabolic tracker spits out an exact measurement.

Having this type of data at your fingertips means you can hack your metabolism by adjusting your diet, nutrition and habits. Sounds nice and simple. And clever!

Essential reading: Roundup of the top 10 smart scales

As far as battery life, Lumen is definitely not something you will be charging often. With normal use you should be able to get about 2 weeks on a single charge. And this jives with my experience. In the roughly three weeks of use (multiple times each day), I only needed to reach for the charger once.

It makes a refreshing change having a health device that doesn’t require charging often. This means if you are going on a trip or simply carrying Lumen around with you – in most cases you can leave the charger at home.

Refueling is done by resting Lumen on top of the docking station. The device will be held securely in place when aligned with the magnetic charging pins. Then plug the USB-C cable into a power outlet and keep an eye on the LED indicator ring.

Lumen breath analyzer review: How to use

  • Setup is simple and intutitive, slick app
  • A measurement can be done in less than a minute
  • Ideally, readings should be done several times per day
  • For best results, follow the nutrition guidelines

Setup and use

Using Lumen is a breeze. But before that you will need to set it up. Like any other device that has rechargeable batteries, make sure to top it up to full before first use. You can use that time to download the iOS or Android smartphone app. Lumen does not display info on readings on the device itself. For that you will need to use the smartphone app.

The software will ask a few questions about you, such as your age, gender, weight and more during the initial setup. It doesn’t take long to complete this and pair Lumen with your smartphone. The process is simple and intuitive. In my experience Lumen connects to the app without fail after the initial Bluetooth pair. Not a single drop in connection or sync issue during my testing.

Optionally, you can also connect your Apple Health or Garmin Connect account to the Lumen smartphone app. This is useful as activity and sleep data will automatically sync.

Lumen review
Premium quality feel about it

The breathalyser is meant to be used a few times per day. For example, you can use it the first thing in the morning, 30 minutes before exercise, 30 minutes after exercise, before eating, and hour or two after eating, after fasting and before sleeping. Or assign your own custom check-in.

This sounds like a lot – and it is. But you don’t need to use it religiously in each case. I tended to take a measurement in the morning, and then perhaps once or twice more during the day. My usage case scenario would differ from day to day. Sometimes I used it before or after eating, or exercise. Or before sleep.

It is worth noting that the device needs about a day to calibrate. This is where it learns the specifics of your metabolism and physiology. A further couple of days are required for all the algorithms to be fine tuned. After that it’s plain sailing.

How to take a CO2 reading with Lumen

The good thing is that taking a reading takes a very short time. Fire up the smartphone app, press the “take a measurement” icon and you will be guided through the process. In most cases, you can complete all of this in less than a minute.

In some usage case scenarios you will be asked to enter a bit more detail. For example, if you are doing a measurement before a workout – you will be asked to specify what type of workout, the duration and intensity. You will then be asked to “Sit, relax and turn on your Lumen”.

After that it’s a matter of inhaling deeply through the Lumen until you are told to stop. There is a circle indicator in the smartphone app telling you when you’ve drawn in enough breath. After 10 seconds, when the ring turns green, you need to exhale slowly. There’s a bar indicator showing whether the intensity you are exhaling at is adequate. You pretty much need to exhale most of the breath that is in your lungs. If you dont inhale enough air beforehand you will not be successful in exhaling enough for a successful reading to take place.

Sometimes you will be asked to take two measurements, sometimes only one. I couldn’t figure out what the criteria was for that.

There are also scenarios when you will be told you have not exhaled properly. It does take a bit of practice and the Lumen metabolism tracker app will walk you through everything. After a few days of use, I found that perhaps one out of 5 or 6 measurements was problematic – and I was asked to do it again. No big deal. It does get easer with practice. But I would not classify it as difficult.

That’s pretty much it as far as taking a measurement. You will then be shown in the Lumen app what fuel source you are currently utilizing. It is on a scale ranging from 1 to 5. The lower down on the scale, the more fat you are burning. The higher up, the more carbs you are using.

Testing ahead of a workout

Let’s say you are planning to do a run or a cycle ride. Ahead of most endurance workouts you should stock up on carbs. A quick test with Lumen 30 minutes before exercise will tell you if you need to carb up further, i.e. if your body has all the energy it requires for the workout. This also depends on the type of exercise. Some workouts do not require as much carbs as others. Fat can also be used up to a point.

The ideal scenario is to wake up in a fat burning state. And then to shift to carbs as the day progresses in order to sustain your activity. Particularly if you are exercising that day.

Lumen review app

A very obvious example which illustrates the importance of carbs is marathon running. Carbs are the primary source of energy for endurance events. This is why 48 hours before the marathon race, it is recommended that you stock up on carbs. The favorite for most people is pasta. Others prefer rice, potatoes and pizza. It is often referred to as carbohydrate loading.

Your body needs this in order to be able to complete the 26.2 mile course. So it’s not just a matter of exercising for months in order to be able to sustain the effort. You need to adopt to a specific diet in order to meet the high energy needs of the event. Otherwise, you might “hit the wall” – a sensation where you are so fatiqued, you are simply unable to continue moving.

Now imagine this for any type of exercise. Depending on the type and duration of workout, your daily carb/fat intake will differ. Tweak this and you’ll be able to improve your performance.

App offers a wealth of data

The Lumen smartphone app displays a timeline of your daily measurements on the “Today” screen. There’s also a weekly pie chart summarizing your readings for the past seven days.

Lumen review app

A longer term timeline can be found in the “Me” section of the app. Every few days, you will be asked to manually enter your weight. This is also charted below the readings. It is important to keep this up to date as it will effect the results the app churns out.

Finally, after about two weeks of regular use you will be assigned something called a Lumen Flex score. I received a 7.5 on a scale that goes from 0 to 21. The goal is to get your metabolism in a state where it is highly flexible. You might be at one level today, but this can be improved by tweaking your diet and nutrition. The app calculates your Flex score based on your body’s ability to burn fat and carbs, along with how closely your body clock is in sync with your daily lifestyle.

The one thing to do is to remember to keep on using Lumen. This is how you will derive the most benefit and learn how to improve your habits. To help with not forgetting, there are notification reminders. Switch these on and the app will fling reminders your way to nudge you into using Lumen.

Nutrition plan

CO2 measurements of your breath are only one part of the package. Which is easy to maintain and understand. The other part is to do with nutrition.

Lumen doesn’t only tell you what you are burning for fuel and how efficient your body is at that. It also tells you what and when to eat. So to make most of the device, ideally you should follow the daily nutrition plan the app spits out.

The nutrition recommendations let you know exactly how many grams of carbs, fat and protein you should consume to achieve your goal. These are based on your vitals stats, along with Lumen CO2 readings in the morning, your activity, and your carb intake the previous day. It is the type of info that requires commitment. Particularly if you are trying to lose weight.

But do you really know exactly how much carbs, fat and protein your daily food intake contains? Most people don’t. And this is where the effort comes in.

I tended to use the daily nutrition plan more as a broad indicator rather than something that I religiously adhered to. But this was enough for my purposes. If I was trying to lose weight, I would have done more to stick to the recommendations.

To make the job easier Lumen offers a detailed guide for breakfast, lunch, snacks and dinner. You can tap on any suggestion to learn the typical amounts of carbs, protein and fat in the serving. These suggestions are based on your daily nutrition plan recommendations. There’s also a section where you can (and should) log your daily carbs, view your daily activity and sleep stats.

Lumen review app

Lumen breath analyzer review: Making sense of the data

  • Takes commitment to make full use of the device
  • Scientific studies confirm accuracy of measurements
  • As do customer reviews

There’s clearly a learning curve involved when using Lumen. So it will take a bit of time for a typical user to be able to digest all the info. It is definitely an educational experience. To help you along the way, the smartphone app is full of descriptions, How-Tos, video walk-throughs and more.

The only way to measure your metabolism up to now has been a costly and time consuming test in clinical settings. This is known as RER and it is referred to as the gold standard. Lumen uses this metric as a core data point. It brings these type of measurements to your home environment for a fraction of the cost and time required.

The CO2 part is easy to understand. You will know at each point in time what your body is burning for fuel. The readings do shift around a bit so you may be both in a pure fat burning and pure carb burning state in the same day. It all depends on your food intake, activity and the specifics of your metabolism.

As mentioned, where it gets more difficult are the insights, actions and nutrition advice. I don’t think it is easy to stick to the minute specifics of the meal plan. So how useful all of this will be to you really depends on how committed you are prepared to be. And what your goals are. If you are trying to lose weight I suggest you do your best to stick to the recommendations.

You can easily carry it around with you

I can see several usage scenarios for Lumen. I don’t struggle with weight but have found the device to be useful as a tool before and after my workout. Knowing whether I am properly fueled each time I head out for a run adds a scientific element around my fitness performance that I wouldn’t otherwise have.

But I feel the device is of even more use to those that are looking to lose weight. Of course, the results will not come overnight. You would be looking at several months of use, at minimum.

Out of interest I sought out other people’s experiences. I typically do not rely on other people’s reviews when testing out a device. In this case it made sense to read what other customers have said. Particularly those that have been using Lumen for longer.

Luckily there are avenues where users experiences can be found. One of these is Trustpilot. Some 350 reviews are up there and they give Lumen an excellent 4.5 out of 5 rating.

Many of these reviews have been written by people who have used Lumen to successfully lose weight over the course of a number of months. The device has improved their eating habits and thought them about healthy weight loss. Some are using Lumen as a tool to help them stick to a particular type of diet, while a few have medical issues so are using the device as an aid for that. It is clear the usage reasons are be vastly different from person to person. That is the beauty of the device.

Scientific studies validating the accuracy of Lumen

The logical question is whether any of this has scientific validity. How good is Lumen at estimating the CO2 in your breath? There really is no way for me to vouch on the preciseness of its readings.

What instills confidence are the scientific research papers which confirm its accuracy. The company mentions several of these on its website. One of them writes.

The above studies conclude the validity of Lumen’s technology as a device that accurately measures changes in metabolic fuel usage, in a comparable manner to the gold standard. The studies concluded Lumen’s ability to identify changes in the metabolic fuel usage following exercise, a change in diet and consumption of a high-carb meal.

There’s also a study that was conducted by the San Francisco State University. It concludes the following.

This study shows the validity of Lumen to estimate metabolic fuel utilization in a comparable manner with the “gold-standard” metabolic cart, conveniently providing real-time metabolic information for users anywhere.

Here’s a link from another peer-reviewed paper. That one was published in JMIR Publications and adds a voice confirming the accuracy of readings.

There is no reason to doubt the validity of scientific studies results. Particularly if they come from a few different sources. But for me personally, the proof is in the pudding. So I have more confidence in the reviews written by customers who have used the device for longer. And they are excellent.

Lumen breath analyzer review: The bottom line, is Lumen worth it?

With just one breath, Lumen tells you what you’re using for energy. It measures the CO2 production in your breath to work out how much energy is being burned from carbohydrates and how much from fat. This allows you to see what’s going on with your body in real-time.

Lumen requires calibration for a day where it learns the ins and outs of your metabolism. It takes a few more days for the algorithms to be fine tuned. But after that you are good to go.

You can use the gizmo each morning to receive direction on how yesterday’s meals and activity are affecting your metabolism. A specific daily goal for carb consumption is then churned out by the app, along with recommended meal combinations. Throughout the day, you can take additional breaths to make sure you’re on track.

The device can, for example, be used to learn whether you have enough energy for an intense workout or need to fuel up. Or to see the impact of your exercise afterwards. There are a few studies which speak positively of its efficacy, too.

I am enjoying using Lumen and would recommend it to those that want to add a scientific element to their workouts. As well to those who want to use it as an aid for weight loss.

Having this type of data at your fingertips will help you learn how your body processes food, and fine tune your metabolism for the better. It is a very cool thing to have in your hand. Think of it as a motivational tool. The caveat is that the device does require daily commitment to derive the most benefit. Some people may not like this.

The personal nutritionist in your pocket can be picked up on Lumen’s website. You can get 10% off by clicking on this link. Just make sure to use the code Gadgets10 at checkout.

The price differs depending on the monthly subscription that you opt for. There’s a “Metabolism Booster” six-month deal for $249 / £249, an ‘Advanced Fat Burn’ 12-month deal for $299 / £299 (without the above discounts), and an ‘Optimal Health’ deal 18-month track for $349 / £349. This is a bit costly but it includes the device itself. Look at it as an investment into your health.

To find out if Lumen is for you, there’s a no risk-free option which lets you use it for a month. Return it before the period ends and you will get your money back.

*We are a review site that receives a small commission from sales of certain items, but the price is the same for you. Purchasing items by clicking on links in this article allows us to run this website. We are independently owned and all opinions expressed here are our own. See our affiliate disclosure page for more details.

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Marko Maslakovic

Marko founded Gadgets & Wearables in 2014, having worked for more than 15 years in the City of London’s financial district. Since then, he has led the company’s charge to become a leading information source on health and fitness gadgets and wearables.

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