Lumen Review – the Bad Bits 💲 Is It Worth It 💲 big discount

Lumen Review Metabolism Discount
A revelation, as Ella realised Lumen had been pointing towards her goals all along

Lumen Review UK & Discount – Burn Fat, Lose Fat and Prove It

This is a detailed review of Lumen for readers in the USA and UK, it starts with a quick summary. Unlike most reviews of Lumen, I’ll delve into the negatives so you can make an informed purchase, however, on balance, it is a good product that works for most people.

Updated: 26 March 2024

I used Lumen for over a year, it’s a handheld device that tracks your metabolism by analyzing the carbon dioxide in your breath. Lumen is a handy and easy-to-use tool for people trying to lose weight or even athletes wanting to assess their lifestyle choices. Lumen helps you understand how your body burns fat and carbs, which is crucial for those on a weight loss journey or aiming for better endurance in sports.

The device offers personalized nutritional advice, follows a keto-style approach, and syncs with Garmin and Apple Watches. It’s often on sale, and there’s usually a discount with an affiliate code. I have a code, THE5KRUNNER, that can be added to ongoing promotions, often saving you over $100. For instance, during Black Friday, using the code the5krunner can get you $100 off and a 50% discount.

CO2 breath analyser
  • Price
  • Apparent Accuracy
  • Build Quality & Design
  • Features, Including App
  • Openness & Compatability

Lumen Review Verdict: A unique and effective tool for a better metabolism, dietary coaching and proof your diet is working

I’ve been using Lumen for over 3 years now, and I can say that it’s the only product that can accurately measure how well your body burns fat and carbs. This is important for losing weight and improving your athletic performance.

Q: What’s the point of losing weight from carbs?

A: None. Anyone can burn carbs. It’s super easy. Burning fat and using it as the default energy source is hard.

Lumen Reviews metabolism review UK discount code reddit price

Lumen is a small, vape-like device that analyzes your breath to help you understand how your body burns fat and carbs. It’s user-friendly and only takes a minute to get a reading. The device connects to the Lumen app, which not only displays your results but also provides personalized nutritional advice, keto-style tips, and links to Garmin and Apple Watches.

In my experience, Lumen was a valuable tool for my weight management journey. It helped me identify what worked and what didn’t. Making simple changes like avoiding late-night eating and extending fasting periods made a noticeable difference, resulting in a quick 1kg weight loss.

Lumen Review Metabolism

Despite years of endurance training, Lumen revealed that I sometimes burn more carbs than expected. While I can’t vouch for absolute accuracy, the device seemed broadly correct, and its readings aligned well with my blood ketone samples. The information provided by Lumen is practical and actionable, with the app guiding me on what steps to take based on the readings.

Lumen also offers free apps for Garmin and Apple Watches, making it convenient to track your carb and fat-burning status. It was reassuring that my partner, who holds a degree in nutrition, supports Lumen’s dietary guidance.

Overall, I’m very pleased with Lumen and would recommend it to anyone looking to enhance their weight loss or athletic performance.



  • Holds you accountable
  • Easy and intuitive to use with instant feedback – literally takes one minute
  • Good recipe ideas, sensible and straightforward dietary guidance
  • Useful apps/widgets for Garmin watches and Apple Watch
  • Simple, easy-to-understand metrics
  • Supports long-term healthy lifestyle, more than simply weight loss
  • Good customer support
  • Optionally, your Garmin prompts you to take readings when you’ve just woken up or just completed a workout.


  • Lumen only works for readings taken at rest, NOT on the go.
  • The results are actionable yet not claimed as medical-grade but Lumen  has peer-review studies
  • Can take a few tries to get the breathing right when taking readings.
  • Fat burn stats might be inaccurate for extremely fit people.

Onboarding & Using Lumen

Customizing the app to suit your preferences and lifestyle might take a bit of time, especially if you decide to connect your Garmin or Apple Watch, which is a bit more intricate than necessary. However, both tasks are quick and only need to be done once.

lumen metabolism


The Lumen inhaler includes a hygiene cap, a USB-C charging stand, and a built-in rechargeable battery that provides more than 50 readings and lasts for a week.

The app setup is a bit more involved than it could be. You have to input personal details, connect to Apple Health/Google Fit, pair with the inhaler, establish a typical workout and sleep schedule, and finally, specify your dietary and fitness goals. Lumen requires all this information for accurate personalization. I use the Garmin link, and it would be more convenient if the app could pull this information directly from Garmin Connect, saving me from entering it twice.


Here are examples of screens you’ll see when connecting Garmin and Lumen. Once you locate your API key (App>Me>Gear Cog>Connect Your Garmin>Connect IQ App !!!), the rest is simple. Just to clarify quickly, a Garmin WIDGET is installed, and you access widgets from your Garmin widget menu, typically reached using the middle left button on a Garmin.


Using Lumen – Basic Usage From This Review

Using the Lumen daily is straightforward, and I encountered no issues with usability during the research and preparation for this review.

To take readings, you need to have the app open and paired with the Lumen device. Simply relax and sit comfortably. While the app may suggest specific times for readings, you can also press the ‘breath’ icon in the top left of the screen whenever you like.

When you breathe in through the Lumen, the process is guided by visual and audio cues. The concentric rings on the screen gradually expand and turn green, signalling you to stop and hold your breath for 10 seconds. Exhale steadily, and a sliding ball on the bottom of the app screen helps you maintain an even breath. It’s easier than it may sound!


lumen review metabolism metabolic

Normally, you take two breaths, which takes about a minute. Your breath is then given a score out of 5, where a LOWER number suggests more FAT is being burned in your body. The goal is to burn fat most of the time for better aerobic fitness, achieved by eating fewer carbs. Lumen indicated to me that I burned more carbs after meals and intense workouts, which aligns with my experience.

CRUCIAL: Pay attention to breathing the same way every time, down to the smallest details of each breath.

In the image, I scored 1/5 (excellent!), indicating that I’m primarily burning fat.

Lumen Review and coffee
Once again, Andrea couldn’t help but worry about the full-fat content of the milk in her coffee and whether it would affect ketosis

Using Lumen, Let’s Review 5 Essential Ways

Whilst the mechanics are the same for every reading you make with Lumen, there are 5 daily events you might optionally want to let Lumen know more about 

  • Morning Fasted measurement – Tap the ‘Take a breath’ button in the morning.
  • Check-in measurements – Tap the ‘wind’ icon on the upper left-hand corner of the screen. Here you take measurements important to you that you want to track over time such as pre-meals, 60-90 minutes after meals, before going to bed, and before breaking your fast.
  • Workout measurements – can be taken by adding a workout to your day – read more
  • Breath Signature measurements – Tap on the ‘breathe now’ button on the breath signature card. These are important, pre-tagged measurements targetted at key metabolic states/times of the day
  • Boost measurements – available on high-carb Boost days.
Lumen Metabolism Discount Review
Lumen has nothing to do with contraception. Evidence: this photo.

Using Lumen to start the day

Lumen relies on a couple of pieces of information.

Firstly, it asks for the number of carb servings you had yesterday (optional) and how long you fasted until breakfast (optional). In my case, as shown below, Lumen also automatically fetches sleep data from Apple Health (Apple Watch), steps from Garmin, and a manual running workout I entered in Lumen.

Next, take your morning Lumen reading which makes an additional assessment of your current fat-burning capabilities. Lumen is also aware of your usual weekly workout schedule, such as a planned 90-minute bike ride today. It compiles all this information to provide you with a daily nutrition plan. I’ve noticed a few recurring themes in the Lumen diet:

  • Generally, Lumen aims toward a Keto-style diet of low-carb
  • Lumen wants you to perform intermittent fasts to continually review and assess your progress
  • Lumen adds higher-carb days, perhaps to counteract some of the negative effects of a rigid keto diet.
  • Carbs are increased for days when planned workouts might need them. Double-check the carb recommendations if you plan extreme workouts.

The daily nutrition plan is presented straightforwardly. At a fundamental level, you can use it as a guide to adjust your macronutrient consumption patterns. If you’re someone who tracks macronutrient intake meticulously, you have the option to make more detailed changes to your diet in line with the recommendations. Personally, I used it as a general guide.


How to Use The Lumen Food Log

The Lumen app has added a food log feature that seamlessly works with other apps like MyFitnessPal. Here are the advantages of using the food log alongside the Lumen metabolism app: Just scan the product barcode and input the quantity you consumed.

  • Easily log meals and ingredients by scanning food labels and barcodes.
  • Understand the impact of specific ingredients on your metabolism in real-time.
  • Determine when and what to eat by measuring the effects of each meal and snack.
  • Focus on the nutritional value and macronutrients of foods rather than just calories.
  • Monitor how certain food types (macros) affect your exercise, sleep, and fasting routines.
  • Import data from other platforms like MyFitnessPal.
As Tabatha picked carbs somewhat nonchalantly, Jane & Tilda were certain their efforts were burning carbs


The crucial moments to take readings for everyone are before bedtime and upon waking. Ideally, your body transitions into fat-burning mode overnight, possibly assisted by quality sleep and avoiding late-night eating. The readings before and after sleep help quantify and track this change throughout the week. I faced some challenges with pre-bed metabolism readings as I typically go to bed after midnight, causing some confusion for Lumen and adding complexity to the review process.

Nevertheless, the ‘wheel’ diagram provides a visual guide to your progress each week. For instance, you can observe a generally good week of morning readings except for Saturday, when I still burned carbs in the morning due to a bit too much wine the previous night.

The second chart illustrates before and after readings for a 1-hour and 18-minute run. In this instance, it was a slow run, and my body correctly shifted towards fat burning.




In addition to those two standard charts, there are interesting tag-based reports too.

Each time you take a reading, you can label it with a phrase that has significance for you, such as ‘before bed,’ ‘waking up,’ ‘before a short, fast run,’ or ‘after a long bike ride.’ It’s recommended to use tags for key moments in your fitness routine. Keep in mind that it’s highly unlikely you’ll end up doing more than four readings a day, so you only need a similar number of tags for the special daily readings you plan to take.

For me, the tags of interest were pre/post/exercise/bed. Throughout my month with Lumen, the Lumen Scores varied at these points in the day, and there was no noticeable trend over the timeframe. One could interpret this as providing confidence in the consistency and quality of the readings or as an indication that I should have closely followed Lumen’s dietary advice for improvement.

Lumen Review Is It Worth It Metabolism
Dave & Daphne debated making a run for it. They’d both had cake.

Using Lumen | Review | More Advanced Usage to Hack Your Metabolism

The more advanced use of Lumen comes into play when you leverage the additional features from the Garmin app integration (widget). These features prompt you to take readings corresponding to different ‘states’ of your body throughout the day. For instance, when you wake up, your Garmin watch will review your status and automatically suggest a morning Lumen metabolism reading since it ‘knows’ you’ve woken up. The same prompt seems to come from my Apple Watch, but I suspect it’s more linked to the time of my morning alarm rather than recognizing that I’ve actually gotten up.

In the next image, you can see an example of being prompted to take a post-workout breath, 30 minutes after completing a 90-minute ride. Again, Garmin knows I’ve finished a workout, so the Lumen widget automatically schedules the reminder.

Taking a reading earlier than 30 minutes after the workout or during the workout would be incorrect. I tested this incorrectly, and some of those readings did show higher carb burning than expected, so I adjusted my approach and followed the Lumen guidelines!


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Lumen’s Garmin App

Once the onboarding is completed, the integration with the Garmin App works well.

Lumen is set up as a widget that reports your recent Lumen fat/carb ratio score and prompts you to take readings when necessary. Events like ‘waking up’ and ’30 minutes after a workout’ trigger reminders from Garmin/Lumen to take a reading. These prompts are driven by intelligence based on events in the day, rather than a predetermined schedule from your Lumen calendar in the app.

The widget display is visually appealing, although the colours on my Forerunner 965 could be improved. It may look better on Garmins with superior screen technology like the Venu. The review image shown on the Garmin Fenix below has been enhanced by Lumen.

At the top of the widget, you see your last synchronized reading and its ‘tag.’ For instance, a 2/5 indicates a mostly-fat-burning morning reading, which is good, but an even better 1/5 reading from yesterday on 10th September is mentioned.

Lastly, there’s the Lumen Flex score. Your body naturally switches between using different proportions of fat and carbs as fuel throughout the day. The Lumen Flex score is a proprietary metric that lets you track and assess how easily the fat-burning metabolism can be activated or deactivated. A higher Lumen flexibility score for your metabolism is beneficial for both athletes and those aiming to lose weight.



Actual Fat/Carbs in Workouts

Let’s step back and understand why we do this for sports.

Your body has limited stores of carbohydrates and can only replenish them at a restricted rate. For longer workouts exceeding an hour, running out of carbs can have disastrous consequences, especially in a race, because relying solely on fat metabolism for energy is too slow for athletes. While this is a complex topic, in simple terms, improving how your body burns fat can push back and eliminate the ‘disaster point.’ For someone aiming to lose weight, the goal is essentially the same: BURN A HIGHER PROPORTION OF FAT.

However, all the apps you’ve encountered only estimate fat and carb usage, usually based on heart rate data (often wrong). Every app is generally similar in this regard, even the professional athletic ones. Take Polar’s fat/carb usage data from workouts as an example. Polar recently added features for analyzing fat/carb burn during workouts. Charts, like the first of these two, can be intimidating but they demonstrate that when you try REALLY hard you rely heavily on carbs. However, it’s essential to note that these are estimations derived from your heart rate, time in a specific zone, and a bit of science.

Lumen is different and measures your carb/fat usage. The reality you measure will be different from the predictions of software tools like Polar (below), perhaps significantly different.

I had initially hoped that in this review, I could use Lumen during a workout to cross-reference metabolism charts like these, but now it seems that might not be possible. It appears that since Lumen only measures CO2 and not O2, the estimates it generates are only considered accurate 30 minutes after workouts. In other words, if taken during a workout, the readings might be inaccurate.



Here are some screenshots from my Apple Watch app.


Notes on Lumen Usage in this Review

  • I suspect that Lumen asks for a 3rd breath when the first two do not agree on the state of your metabolism. On occasions when I didn’t inhale or exhale correctly, a 3rd breath seemed to be required. And on a few of those occasions, I wasn’t convinced by the Lumen score it gave. Over the years Lumen seems to ask less for 3 readings. Maybe I’ve got better at doing it!
  • If you hyperventilate before taking a reading, the fat burn score improves. The point of saying this is that if you want meaningful readings you have to perform sensible tests, in the same manner, each time.
  • Breath Reading Tips:
    1. Breathe out before starting, and empty your lungs of CO2-rich stale air.
    2. Breathe in a little extra air after you have the green ring.
    3. Between readings, empty and refill your lungs at least twice.
    4. Don’t hold excess air in your mouth when you hold your breath.
  • As part of the research for this review, I found that the consistency of the breath flow rate seems to be important for Lumen to secure a correct metabolism reading. Try to be consistent.
  • Lumen requires 5 minutes between sets of readings. I have taken a series of readings separated by 5 minutes, and they can vary by +/- one point on Lumen’s scale. That variance could be down to inaccuracies in the device or in the process I am using. For example, it is possible to start inhaling before using Lumen, and it is possible to hold inhaled air in your mouth… do these make a difference? Possibly, I don’t know. Be consistent!
  • If you check the comments section, below, you will see a specific physiological case where Lumen gives incorrect readings, i.e., when you are in a state of deep ketosis.
  • I lost 1 kg when I used Lumen for over a month. I’m trying to lose 1 kg more. That loss is a statement of fact measured by my Garmin Index Scale 2 every morning in the same state. I attribute the success to being more aware of food and eating less. I also tended to eat my last meal earlier. #CalorieDeficit.
lumen review metabolism metabolic
I did lose 1kg!

Lumen – Some Science, Tests & Limitations Brought out in the Review

Lumen has now published peer-reviewed science to support the efficacy of its product. See


Lumen claims this

Lumen’s technology has been scientifically proven to accurately measure metabolic fuel usage when compared to the gold standard (RER) for measuring metabolism in multiple validation studies.

Lumen has this page which cites studies by Lorenz et al and Mor & Mor, both studies have Lumen employees involved and one is peer-reviewed. Having employees involved in the research is not unusual! Nor is sponsored science, this is relatively common practice amongst many of the health/nutrition products you buy. Now that some of the work is peer-reviewed that adds credibility to the claims.

I pointed out to Lumen that their device does not contain an O2 sensor and that an O2 sensor is typical in medical-grade RER devices. They replied,

Measuring the CO2 concentration in one’s exhalation can be used as an indicator to one’s metabolic fuel dynamics according to the following principles:

  1. Cells that use carbs as fuel produce more CO2 (relative to the consumption of oxygen) compared to when they use fat.
  2. In a rested condition, the oxygen consumed does not change dramatically, so a subject’s Respiratory Quotient would be mostly represented by changes in CO2 production.
  3. The CO2 concentration in mix venous blood correlates to the metabolic fuel dynamic.
  4. The breath-holding technique enables us to determine the CO2 concentration in mix venous blood.

In order to provide fully clear results with Lumen it is therefore important that one is entirely at rest when taking a measurement. 

I am not a scientist but have read Lumen’s metabolism studies, linked above, as part of my research for this review. You can make your judgement but they seem reasonable to me in terms of what they say, certainly, more can be done and more can be clarified, that said some of the research is now peer-reviewed.

For me to get a layman’s view of the correctness of the data is tricky. An RER test in a medical lab is an option that I could have done, they take time and are expensive. Handily, I do have a ketone + glucose blood reader from my look at HVMN a while back. So I used that 🙂


My starting point was that blood ketone levels above 3mM usually indicate ketosis. While there are reasons why a breath test might yield different results from blood or urine ketone tests, I anticipated a general agreement.

Here’s what I discovered:

I conducted 4 tests, and each time Lumen reported a fat-burning score of 2/5 or 1/5. Concurrently, my blood ketones were above 3.0 on 3 occasions and below 3.0 on the 4th. For a non-invasive test, I found this to be ‘reasonable’ but not necessarily scientifically conclusive. On the 3 occasions with higher fat-burning levels, they occurred after long, easy morning workouts (without eating late at night), which was expected.

However, fasting for 14+ hours didn’t consistently result in Lumen reporting a fat-burning state for me, and I did NOT anticipate that. This discrepancy might occur because a deep state of ketosis can produce more CO2, potentially leading to a false positive for carb burning.


lumen review metabolism metabolic

Lumen Frequently Asked Questions

Q: Is Lumen Accurate?

A: After nearly 2 years of use, I would say Lumen is accurate for all of us in most normal situations. Lumen publishes scientific papers that claim accuracy in specific circumstances. My own limited and unscientific testing found occasions where Lumen’s results matched results on ketone strips as well as my expected results. Some results didn’t match.

Q: What is a good lumen flex score?

A: 21 is a perfect score and anything over 15 is good. Average scores range upwards from 7.

Q: Does Lumen Work?

A: Yes. In my opinion, Lumen is certainly sensing carbon dioxide and inferring carb/fat consumption. It’s not just making the number up. However, I can’t say from my own experience if it has medical-grade results.

Q: Can I use Lumen without a subscription?

A: No.

Q: Does Lumen Work with Apple Watch?

A: Yes, kinda. Lumen works primarily with an app on your smartphone. However, there are Apple and Garmin apps that offer extra (free) features on your favourite watch.

Q: How good is Lumen?

A: I’d say it’s good. Lumen has put together a good package of an inhaler and software with some cool insights for athletes and those on diets.

Q: What is the Lumen metabolism Tracker?

A: The Lumen device is like an inhaler and measures the flow of air and its CO2 content. From that, it infers your fat/carb usage and further assumes you are rested.

Q: What are the alternatives to the Lumen metabolism tracker?

A: One alternative to Lumen is the Breezing Starter Kit, I’ve not used it and it has highly indifferent consumer reviews. Trustpilot has great review feedback on Lumen which, of course, doesn’t prove it’s scientifically accurate but it does show that users are generally very happy with the product. Foodmarble is another alternative that analyses the hydrogen content of your breath. However, as far as I know, there are no consumer-grade competitors to Lumen that measure fat burn from breath signatures.

Q: What were previous generation Lumen devices?

A: There has only been one version of Lumen. This is the original version and there is no planned replacement or upgrade that I know of.

Lumen Specifications

These specs are here for completeness and I’ll draw your attention to a couple of features not covered elsewhere in the Lumen Review like a maximum of 14 days of battery life and the need for iOS/Android version 8.

Lumen Technical Specifications 
iOS compatibility (iOS 8 and higher)iPhone 6 and more recent
Android compatibility (8.0 and higher)Recommended higher than 720 x 1280 pixels
Bluetooth connectivityBluetooth Low Energy needed
Application connectivityApple Health Kit, Google Fit
Operating temperature: 15°C to 40°C (59°F to 104°)
Storage temperature: -30°C to 70°C (-22°F to 158°)
SensorsCO2 sensor
Single battery charge lastsUp to 14 days in normal use
BatteryLithium polymer battery
Lumen device dimensions102mm x 41.4mm x 33.3mm
Lumen device Weight75g
Docking station dimensions14.5mm x 79.5mm x 68mm
Docking Station Weight145g
Charging Connections:USB-C (cable provided)


Lumen Resources

Lumen has some great resources on its app but for those of you interested in learning more before you buy it their site is a great place too.

Link to: Lumen Knowledge Base

Lumen Discount Review
Shazia felt dumb, why didn’t she wear the white outfit? Why!

Lumen – A Quick Take Out

Lumen’s claim to accurately assess fat/carb burn for most people, most of the time seems reasonable, based on my months of usage.

As far as I know, no other consumer-grade product can measure fat/carb consumption, making the information Lumen provides highly actionable, whether you’re dieting or striving to enhance endurance.

For athletes, Lumen offers precise feedback, available on both its smartphone apps and directly on Garmin and Apple watches.

For those focusing on weight loss, Lumen provides added value by guiding you through a responsible, keto-style diet. It showcases your improved ability to burn more fat, a crucial factor in losing weight.

In my opinion, Lumen stands out as a unique and impressive product.


Lumen gets a respectable Trustpilot score plus some good feedback on Reddit too.

Lumen Metabolism Review – Price, Discounts & Availability

The Lumen device is now available for a frequently discounted price below the rrp/MSRP of $299/£299/Eu299. Nutritional guidance and other app features are accessed by a new, cheaper, subscription at $19/£19/Eu19 a month.

Currently, my code THE5KRUNNER gives you $/£/Eu50 off, a 1-month free subscription and free delivery in most countries.

Lumen is in stock and available directly from the manufacturer with a 30-day no-quibble guarantee and there are usually discounts to be found. I’ll add the Amazon link below if/when Lumen is listed there.

I’ve got an ADDITIONAL code for readers of this site. That code is THE5KRUNNER and that will give you an EXTRA $30/£30 off AT ANY TIME.  ie both offers work together. This code should work over and above any discounts Lumen offers directly.

You can get a further 10% off if you order two (ie 3 deals together in one) 

Note the LUMEN SALE and the 2-for-1 deals are automatically applied in Lumen checkout. My discount code: THE5KRUNNER is the only code to add manually.

Order HERE, or click one of the Lumen images and use the code THE5KRUNNER

Lumen Best Rrice and Discount
Roger had always thought the cat would come between him and his relationship with Gemma


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