Lumen Review by latestfuels

Lumen Review | Why I Am So Impressed after 4 Weeks of Testing

Welcome to the king of all Lumen reviews; Latestfuel’s in-depth look at the metabolic tracker that is meant to help hack your metabolism.

When I first heard about Lumen, I was confused. I wasn’t sure what it was, or what it did.

In essence, it tells you what your body is consuming as fuel from a single breath. After exhaling through it, Lumen is able to show you whether you are burning fats or carbs. Sounds cool, doesn’t it?

I was intrigued. Therefore, I decided to test Lumen, using it daily for 4+ weeks. Here, in this Lumen review, I report the journey, analyze the tech, highlight its pros/cons, and ultimately decide if this is a tool worth buying (spoilers in the title).

Note: It’s been over 12 months, but I still use Lumen daily. It helps me keep track of my progress and make sure I’m doing my best when it comes to nutrition.

Lumen Review at a Glance

Lumen metabolic tracker review
LF RatingRecommended
User RatingsVery Positive
  1. Premium quality materials and strong build
  2. Good accuracy
  3. Useful for long term weight loss
  4. Clean app, with insightful information and guidance
  5. Nutrition guidelines and recipes are very helpful, especially for newbies
  6. Clean interface
  7. Integration with Google Fit, Garmin, Apple Health
  8. Tool is being updated continuously – more integrations, better functionalities etc.
  9. 1 year warranty, fast shipping
  10. Easy to use, fast, convenient and unlimited
  1. Lacks a few key functionalities
  2. Garmin integration is finicky, and does not make use to the fool extent of the Garmin data
  3. You need your phone to take measurements
  4. The provided USBC cable is a little too short
  5. It’s not cheap
  6. Yearly subscription payment

What’s in the Box?

Like most tech reviews, I thought it would be appropriate to start with a little unboxing. What does Lumen give you when you purchase its metabolic analyzer?

Lumen inside the box
Lumen Unboxed: a charging cable, a charging dock, a small pouch to take Lumen with you, the device, and some guides to help you get started.

What’s in the Box

  • 1x Lumen Device
  • 1x USB-C charging cable
  • 1x charging pod
  • 1x travel pouch
  • A welcome guide, the warranty, instructions and a thank you note.

Everything Feels Premium

The first thing you notice when you get the box is the premium look: glossy, simple and elegant. It has clear Apple vibes.

Lumen premium review

However, it does not end there and to my surprise all the materials within the box are stupendous. Heck, even the charging cable (although a little short), it’s much thicker than what you get with your phone.

The Lumen device itself is splendid in build quality. It’s heavy, substantial and by no means fragile. It has a nice matte black finish that hides your fingerprints and looks great in person. Furthermore, the mouthpiece and the cover are made of metal; and have a magnetic closing.

Even the charging pod was heavier than expected. It has rubber on the bottom not to scratch the surfaces and not to slide.

Few Small Nuisances

Therefore, I must say that in terms of quality Lumen definitely delivers what’s expected from the price point, even surpasses it.

There are just a couple of small issues that I would’ve like to see improved:

  • USB-C cable is too short. Being just 85cm long (33.5 inches), it’s not going to be long enough to reach the bottom of the table (if the dock is placed there).
  • The device wobbles in the charging dock. You’ll find no stability issues, or connection issues; but it’s a bit annoying that it doesn’t lock more firmly.
  • The ON button is not very satisfying to click. It might sound stupid, but when everything else feels so nice to touch, the ON button fails to deliver the impression you are clicking on it.

Final Opinion – Is Lumen Worth It?

So, after 4 weeks one year of regular use of Lumen, what are my final thoughts on the metabolic tracker?

Should You Buy Lumen?

Perhaps, this is the most important question for many of you. The boring answer is it depends. However, I would be comfortable saying that Lumen is a fantastic device and that I intend to keep using it after this review.

Is Lumen worth the price tag to you, then? Should you spend ~$300 on Lumen?

  • You have a limited budget. If you are just starting and have a limited budget, I would recommend looking to other health gadgets. My personal recommendation would be a smartwatch, since it has more functionalities and it would be of more help.
  • Looking for short-term weight loss. Then it’s not worth spending this money on Lumen. You better get a dietician or a gym membership.

  • Want to maximize your health. Being on top of your metabolic flexibility will have a direct positive impact on your health (discussed below).
  • You need an easy and convenient way to track what your body is burning for fuel.
  • Long-term health benefits. Finally, when used in combination with other fitness tools, it will help you tackle two key areas of a healthy lifestyle at once: nutrition and exercise.
  • Long-term sustained weight loss.
  • Keto users, so that they don’t have to rely on ketone strips (which in the long run will be more expensive).
Lumen and Garmin
On its own, a smartwatch like Garmin might be a more useful health tracking tool. In combination, they are exceptional.

Lumen’s Limitations

I also want to highlight that despite quite liking this metabolic tracker, I think there are some inherent limitations at the current date.

  • The data that is provided is not very actionable. Knowing what your body is burning for fuel is cool, but what’s the actual value of this information? How are you going to use it to improve your health?
  • I think that Lumen needs more functionalities. Since my initial thoughts, Lumen has improved massively in this area. However, I think that Lumen should also focus on exercise, given that this is the most influential factor in metabolic flexibility.
  • Integration with Garmin/Google Fit is limited. You still need to log your workout, sleep times, etc. Given the amount of health-related data smartwatches provide, Lumen should make more use of it. It could then use it to suggest the next workouts, for example.
  • You need your phone and WiFi to use Lumen. This was quite annoying since I couldn’t just take my breathalyzer and use it on the go.
  • Workouts are tracked with time not intensity. Fixed. I would still like to see Lumen taking this info from smartwatches were possible.

I like the reminders to perform a check-in after tla workout. I’d like to be able to snooze them till it’s time for the check-in, otherwise I tend to forget. I’d also like to have workouts synced automatically to the Lumen app. They can get rounded to the closest 5 minute mark (or 15? Maybe make it configurable?). No point in inputting the data manually. As for the widget, seeing my Lumen flex score is of little value, as it isn’t actionable. I’d much rather see the recommended carb serving for today, based on the daily recommendation and workout data. Or even better, if Lumen integrated with Myfitnesspal, remaining carb serving based on up to date consumption. All in all, I like Lumen and it’s Garmin integration into the Lumen app. The other way around is minimally valuable at the moment.

Review on the Garmin store

Limitations on this Lumen Review

Now regarding the personal biases and restrictions in this Lumen review, there are a few that I would like to highlight.

  • I don’t follow a keto diet. I assume that knowing that you are burning fats it’s more important for those who are on a keto diet. The breathing measurements can be a very convenient way to know if you are in ketosis.
  • I didn’t follow the nutrition plan provided. Due to my knowledge of nutrition and social constrictions, I was not following the macros that Lumen provided me with. I think that this is more useful for newcomers that need support or those who want to take their diet more seriously (due to weight loss or other reasons).
  • Garmin – Lumen connection not working properly. Apparently, I’m not the only one, but the Garmin – Lumen integration was not working 100% (particularly on the Garmin end).

What I Would Like to See From Lumen in the Future

Finally, this brings us back to what I would like to see improved on the Lumen.

  • More functionalities. A year after the initial review, Lumen has integrated many more functionalities, and I’m extremely happy to see the progress. The app offers a lot more than it used to do (tracking your food more effectively, for instance).
  • Better and more integrations with key fitness apps. I mentioned my issues with Garmin (and it seems that Lumen is trying to do more with them), but integration with apps like MyFitnessPal would also be great.
  • A small screen on the device, so I don’t need the phone.

How Does Lumen Work?

Once we covered what you get when you buy Lumen’s metabolic tracker, let’s try to understand how it really works.

The Science

As I’ve mentioned various times during this Lumen review, they describe their device as a metabolic tracker or metabolism tracker. But what does exactly this mean? What’s metabolism and how can this help you?

Metabolism and Metabolic Flexibility

Metabolism refers to all the chemical processes that happen ubiquitously in your body; such as, breathing, breaking down cells, creating new ones, digesting food etc. Because each process requires energy to happen, metabolism is closely related to nutrition (the way we get energy in our bodies).

Metabolism simplified. How we get energy and how we use it.

In fact, we often hear the terms slow metabolism or fast metabolism in regards to how fast we are able to process food and spend that energy. However, this is more often than not a misinterpretation of our basal metabolic rate (BMR) – i.e. the minimum amount of energy the body needs to survive for a day.

We generate this energy from food – mostly carbohydrates and fats. In the default setting, the body burns mostly carbs, as it’s easier and faster. However, once we deplete the carb storage, the body can switch to burning fats.

Metabolic flexibility refers to the idea that we can manipulate and enhance this switch in metabolism (carb-burning to fat-burning and vice versa). We could improve the adaptation in fuel consumption in regards to nutrient availability.

According to Lumen, increasing our metabolic flexibility can have multiple positive effects; like a stronger immune system, feeling more energized, better overall health etc.

Benefits of metabolic flexibility
Benefits of metabolic flexibility according to Lumen.

Science Behind Metabolic Flexibility

  • People with diabetes and obesity tend to suffer from metabolic inflexibility. This refers to impaired ability to use adequate fuel and switch between carb and fat consumption.
  • Metabolic inflexibility has been associated with obesity, metabolic syndrome and insulin resistance, and can be improved by exercise or weight loss. 
  • Exercise can have a profound influence and requires metabolic flexibility.
  • Can nutrition affect metabolic flexibility? Can we manipulate and enhance it via a selection of fuels (carbs, fats)? Research is still being done in this area, and for sure it does not have the same influence as exercise.
  • Short-term diet changes were not enough to improve metabolic flexibility.

Key Takeaway: Metabolic flexibility is part of a healthy process, and inflexibility is often a sign of diseases. Exercise is one of the key influencers and necessary to improve it. Nutrition, on the other hand, is relevant, but not enough to fully manipulate it. There’s more research to be done.

How Does Lumen Metabolism Tracker Work?

Perhaps, I’ve gone overboard explaining what metabolic flexibility is. However, I thought it was important to know the basis on which Lumen operates or what it is for.

So how does Lumen track your metabolism? In short, they measure the CO2 levels in your breath. This, in turn, dictates if your body is currently mostly burning fats or carbs.

Lumen RER metabolic measurement
Lumen metabolism tracker relies on the RER values.

This is called the respiratory exchange ratio, and it’s a scientifically validated method of measurement. They compared the ratio of CO2 that you exhale vs the O2 that you inhale (picture shown above):

  • A RER value of 1 means that carbs are being used for fuel,
  • A RER value of 0.82 suggests protein breakdown,
  • And a RER value of 0.7 indicates fats are being burnt for calories.

Is Lumen Accurate? Can I Trust My Lumen?

In a study by the San Francisco State University, it was found out that their metabolic tracker “can provide valid information regarding an individual’s metabolic state”, comparable to the gold standards of the industry. However, 2 of the researchers worked for Lumen parent company, Metaflow Ltd (see possible conflict of interest).

Nonetheless, Lumen seems to be sure of their technology:

is Lumen accurate
Lumen accuracy compared to clinical RET devices.
  • The founders have previously conducted their own research on their device.
  • Lumen is being used in a prediabetes clinical trial.

Take away: For now, the technology seems to work as intended, and it’s based on actual scientific methodologies that are used in professional environments. However, more 3rd party research is needed, even if Lumen’s data seems to be accurate.

Personal Experience

From my experience, I mostly got the results that I would’ve expected. Once or twice, I had surprising measurements, e.g. burning fats after a high-carb meal. This anecdotal experience is backed up by other expert reviews I’ve read.

Nonetheless, for best accuracy it’s important you follow the guidelines:

  • Do not measure with an elevated heart rate. This can negatively affect the CO2 readings.
  • Wait 30 minutes after your workout or after you wake up. Hormonal activation (cortisol), elevated heart rate, etc. can also influence your Lumen level.

Starting with Lumen

Once we’ve covered all the scientific basics, it’s time to turn on our Lumen and discover how to use it.

Setting Lumen Up

Before you start using your Lumen device there are two things you need to do:

  • Charge it.
  • Download the Lumen App from your app store.

In fact, one of the biggest downsides is that you cannot use Lumen without your phone. You will need it not only to log in and track your progress, but also to do the measurements. I hope that in the future they add a screen to the device to get rid of this constriction.

Using Your Lumen for the First Time

Once you download the app, you will be asked a series of questions. This will be used to customize the algorithm to your needs.

This is a simple process that should take you no longer than 5 minutes. To Lumen’s credit, it’s an easy and beautiful procedure; even for those who are not experts in nutrition or phones.

So, once you’ve linked your Lumen to your phone via Bluetooth, you’ll be able to do your first measurement. In order to do so, you click on the air button on the right bottom corner and you can start the process:

  1. Make sure you are in a relaxed position (e.g. sitting).
  2. Put your Lumen in your mouth and inhale when the app tells you so. If you find it hard to inhale for that long (takes practice), my recommendation is to breathe in slowly (small volumes of air).
  3. Once the ring is green, take the device off your mouth and hold your breath for 10s (you’ll see it displayed in the app).
  4. Exhale at the pace that the app indicates (between the two red lines). Make sure you don’t breathe out too strongly.
  5. Finally, the app will display in which state your body is.

Understanding the Lumen Levels

In the final picture shown above, you can see a number from 1 to 5. These are so-called Lumen levels, and indicate your metabolic state. As displayed below:

  1. You are burning 84-100% fat for energy.
  2. Using mostly fats; from 63 to 80%.
  3. You are using both fats and carbs, 42-60% fats.
  4. Carbs are mostly being used; 60-77% carbs.
  5. You are running on carbs for energy, 80-100%.
Lumen metabolic levels

Is one level healthier than the others? Should you be on level 1 constantly? If you are asking these, the answer is no. Part of the aim of using Lumen is to switch between the levels to improve your metabolic efficiency.

However, if you are following a keto diet, then yes, you should be on the first 2 levels constantly.

What Does Lumen Offer You?

So by now, you are probably getting a grasp of the functionality of Lumen’s metabolism tracker. It’s a cool tool that enables you to know what your body is burning for fuel.

Interesting, but is it useful enough?

This was at least my impression after the first day. I wasn’t convinced that what Lumen offered was meaningful to make a difference in my diet/health.

However, as days went by I started to realize the full potential as I discovered the extra functionalities of the Lumen app.

This is the Lumen app review and what it offers:

  • Nutritional guidance
  • Recipes that adapt to your daily recommendations
  • Integration with fitness apps to improve suggestions
  • Lumen Flex – a score indicating your metabolic flexibility
  • In-depth tracking of your habits: lumen metabolism review (metabolic score), sleep, steps, carbs consumed…
  • Weekly metabolism report sent to your email

Nutritional Guidance

For instance, Lumen provides you with personalized nutritional guidance based on your metabolic measurements, activity levels, and sleep. This nutritional guidance is flexible even throughout the day. Thus, it’s designed to boost your performance and energy levels.

As you can see, my daily recommendations changed during the day once I added my workout to the Lumen app.

Notice that the nutrition plan from Lumen is based on macros (fats, protein, carbs), instead of calories. There’s an in-depth explanation on the Lumen app to why this is; but the summary is that they believe not all calories are equal

Recipe Ideas

For that reason, not only do they provide you with the macros; but you can also find healthy recipe ideas.

This is another area I didn’t use much, since I rely on meal replacements to control my nutrition. That said, it can be incredibly useful and a great way to start improving your diet. The convenience and quality of the recipes is undeniable.

In fact, Lumen’s recipe implementation is superb:

  • Provides you with meals that suit your macros – changes depending on what you need next
  • Recipes that are simple, yet you are offered alternative ingredients
  • You can make sure to remove allergens and food that you don’t eat, so that they only show you recipes that fit you
  • Different recipes for each meal

However, some of the ingredients for the recipes might be hard to source on the day. Therefore, I think that a suggestion of things to buy for the week could be really helpful, or an implementation with a meal delivery service that provides you with adequate meals.

In my case, I tend to fill the macros using healthy meal replacements for the most part. These provide me flexibility, and can be prepared within a minute.

Integration with Fitness Apps

Besides the nutritional aspect, Lumen also connects with popular fitness apps like Garmin, Google Fit or Apple Health. This is really important since -like previously discussed – physical exercise is the main factor for metabolic flexibility.

Integration with Fitness Apps Lumen
There’s still room for improvement on the integration of the various fitness apps with Lumen. Not only I had issues with my Garmin, but I also think that there could be better usage of the data.

The integration leaves a lot to be desired (discussed below). I did not have the best experience with my Garmin watch, for instance. However, Lumen is working with Garmin to add more features. Therefore, I expect this to improve drastically in the future.

Lumen Garmin pairing
Lumen Garmin integration. Currently, the app is not very good, but there will be improvements according to Lumen.

Lumen Flex

After two weeks of regular use of your Lumen, you will get your Lumen Flex score. This will be an indication of your metabolic flexibility. The higher the score, the more adaptable your body is to burning different types of fuel.

As discussed in the “how it works” section, being metabolically flexible is a sign of good health. In a healthy body, you should be able to swap between fat burn and carb burn at ease. Hence, keeping track of your Lumen Flex score will be important in assessing your health.

Lumen Flex score reviewed
The end game. After 2 weeks you will get a Lumen score, which will represent your body’s flexibility to switch between fuels and health.

More about Lumen

Lumen logo

Lumen is the child of two twin sisters, Merav and Michal, who have PhDs in Physiology and have won Ironmans. It was born from their drive to create a more affordable and convenient way to track metabolism.

Their aim is to provide tools for everybody to have personalized nutrition that would empower their health.

Merav Michal Lumen co founders
Merav and Michal, Lumen co-founders.


The current price of the device is $349, but you can often find a $50 discount on the retail price. There’s also a 10% discount when you purchase your second Lumen device.

While this is expensive and should act as a barrier of entry; most high-end health tracking tools are worth $300 or more. For instance, my Garmin Fenix watch cost $400 at launch, and it’s worth every penny.

Whether Lumen is worth this price tag will depend on you. As discussed below, I think that this could be a very interesting tool for those who are serious about tracking their health, or need support when starting to do so.


As for shipping, it will be free for the US. In my experience, the delivery was ultra fast and smooth.

Similarly, you will get free shipping to the UK.

For Europe, the shipping fees will be around $25, and for other places in the world will vary. That said, delivery will still be incredibly swift.

My Lumen Experience Reviewed

Over this Lumen review, I’ve discussed the tech, the build quality, the science behind the metabolic tracker and what the app offers. However, I’ve not talked about my personal experience with the device and the subjective topic of whether I think Lumen is worth it or not.

First Impressions

My first interaction with Lumen was a mixed bag. On one hand, I loved their presentation, the unboxing and the general quality of the device, as well as the app.

Lumen Charging
Lumen’s charging animation is almost relaxing.

It was really easy to set up, and the steps to follow are clearly outlined. Plus, the app is visually very appealing. I was excited and ready to try it.

However, this is where my disappointments began. On the first day, besides measuring my metabolic state there was nothing else I could do. There were no nutrition guidelines, no Lumen Flex (unlocked after two weeks of usage), and generally, the App seemed empty.

This was about to change, though.

Living With Lumen

Nonetheless, the second day was a whole different experience. When I logged in my morning measurement, Lumen started coming to life.

With this new log, I unlocked my daily macro suggestion; and the nutrition section. There, I was able to see how many carbs, fats, and protein I should consume during the day. Plus, which recipes would suit my needs.

Encouraged by these new features, I diligently measured my metabolic state at different points during the day. Prior and post-workout, before and after eating, etc.

With this, I was able to track the changes in my body; and little by little I started understanding the value of Lumen.

Lumen Daily Overview
Daily overview by Lumen. Steps and floors climbed was provided by my Garmin watch. An overnight fast is introduced manually.

The value that Lumen provides becomes even more apparent on the third day. As shown above, I was welcomed with a summary of the previous day. Furthermore, I saw the app adapting to my needs; according to what I did the day before.

After that, Lumen became part of my daily routine. I would check during the mornings, log in my workouts, and semi-regularly do extra breath measurements during the day.


Who is Lumen for?

Lumen is for everybody who wants to keep track of their metabolic health and nutrition; and has the budget to afford it. It will give you accurate readings of what your body is burning, and suggestions to improve your metabolic flexibility.

Is Lumen a good tool to measure ketosis?

Lumen does not directly measure your ketosis or ketone bodies; however, it can tell you if you are burning fats or not. Thus, it can be incredibly useful for people doing keto. You will be able to track if you are burning fats easily, and without having to buy ketone strips constantly.

Is Lumen available for Android or iPhone?

Lumen can be used in conjunction with both.

Will Lumen improve my fitness?

It’s not a tool directed to improve your fitness, and it’s more focused on nutrition. However, in conjunction with a smartwatch, workout plans etc. could be a useful extra gadget.

Is Lumen only for Athletes?

No, anybody can make use of Lumen.

What is a metabolic tracker?

I explain this in more detail in the appropriate section. However, in short, it’s a device that tells you what your body is burning for fuel: carbs or fats.

Does Lumen work?

According to 3rd party tests, personal testing, and other experts’ experiences, Lumen works and it’s fairly accurate.

What does Lumen measure?

The device measures your O2 intake and C02 output to determine your metabolic state. Or in other words, if you are using fats or carbs to get your energy.

Can I use Lumen for weight loss?

Yes, you can. In fact, they will provide you with nutrition plans according to your goals. Following these will help you with your weight loss.

Another Lumen review, with which I agree on many points.

Verdict – Lumen Metabolic Tracker Review

All in all, I was greatly impressed with Lumen during the review.

Despite my initial doubts, Lumen was able to win me over. I love the simplicity and ease with which you can accurately measure your metabolic state. Plus, the device feels premium and it’s built to last.

After 6 weeks of regularly using the Lumen metabolism tracker, I’m convinced of its effectiveness and usefulness. In fact, I plan to keep using Lumen after this review to track my metabolic health.

It’s been over a year and Lumen has become one of my daily health tools.

It’s a great way to keep track of what your body is using for fuel. Consequently, it can be a valid alternative for ketone strips and one that will save you some money in the long run.

Plus, I also think it can be used for long-term sustained weight loss, as well as, improving overall health. I would use it in conjunction with the best meal replacements and occasionally some natural fat burners.

The Lumen app itself is sophisticated, clean, and full of information. Furthermore, there’s room for improvement on the software -and one year after the review, many of my initial “issues” with the app have been tackled. Thus, Lumen just keeps getting better, and more useful with time.

In fact, I believe that Lumen offers a lot more value now than it used to 12 months ago (and I have not paid anything extra).

Note: to the point above, during the 12 months of using Lumen, the app has been updated regularly and they’ve fixed few issues I mentioned here.

Hence, even if $300 is certainly not cheap, I believe that you will get what you paid for and much more.

Lumen Review

From $249

Build Quality & Design






Features & Integrations





  • Premium build quality
  • Clean, informative app
  • Seems to be accurate
  • Software updates keep improving the functionality
  • Easy and convenient way to track your metabolic state


  • It's expensive
  • Some of the features can be improved upon
  • Need your phone to use it
  • Requires WIFI connection
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