Lumen Review | A Metabolism Tracker To Boost Metabolism, In The Right Hands

This breathalyzer and smart app system is designed to help you develop a more efficient metabolism and supports healthy weight loss.


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This Lumen metabolism tracker review covers the world’s first hand-held, portable device for measuring metabolism, used by people from many different backgrounds to support their weight loss or other metabolic health and fitness goals. Included in this review is an overview of the key features of the Lumen device, how it works, my experience using it, the pros and cons, cost, and where to buy.

Lumen claims it’s the ‘first device to hack your metabolism’, with the goal of helping you enhance fat burn, lose weight and boost energy… naturally. It does this by using a CO2 sensor and flow meter to analyze the level of CO2 concentration in a single breath.

The CO2 level you breathe out into this breath analyzer provides an indication of the type of fuel your body is using to create energy, on a scale between carbs and fats.

The technology used by the Lumen device has been around in labs and medical facilities for some time, but now it’s available directly to you, and provides you with an analysis that takes a couple of minutes, together with an app integration that offers food logging and exercise tracking.

Lumen Metabolism Tracker Review – Table of Contents

  • What is the Lumen device and what does it do?
  • Why track your metabolism?
  • Key features of the Lumen breath analyzer and app
  • My experience using the Lumen metabolism tracker
  • Cost and where to buy [PLUS our exclusive discount code!]
  • Lumen review summary with pros and cons
  • Image gallery

What is the Lumen device, what does it do, and does Lumen really work?

What is Lumen

Lumen is a small, portable, handheld device that you breathe through to get a reading that it uses to share information on your metabolic state.

The Lumen device analyzes the level of CO2 in your breath to provide data that allows you to monitor and track your metabolism, primarily by learning when you are burning fat vs when you’re in carb burning mode, relative to the timing and nature of what you eat, the exercise you do and when you go to bed and wake up.

Me with the Lumen metabolism tracker - isn't it cute?!
Me with the Lumen metabolism tracker – isn’t it cute?!

Two of the company’s founders are sisters – both endurance athletes, as well as doctors of physiology.

One of the initial goals behind creating Lumen was to help better understand the impacts of nutrition and workouts on your body, with a view to improving athletic performance.

Needless to say, as an endurance runner myself, I was interested to see how Lumen could also help me understand my body better as I work toward my own fitness, training, goal to lose weight.

How Lumen works

This breath analyzer enables you to regularly track your metabolism and gather information on how your sleep, activity level, and nutrition affect it.

With this knowledge, you can tailor your nutrition and activity levels to better work towards fitness goals and achieve metabolic flexibility (more on that later) as well as support your healthy diet or weight loss plans.

Lumen Metabolism Tracker Review Trail and Kale web wm 6

Using the data gathered through breathalyzing, the Lumen app that accompanies the Lumen metabolism tracker then provides you with personalized meal plans, as well as insights on how your sleep and activity level affect your metabolism.

I set up my profile in the Lumen App to focus on achieving healthy weight loss
I set up my profile in the Lumen App to focus on achieving healthy weight loss and stable metabolic health

By breathing through the Lumen device several times a day, you’re able to track your metabolism and learn how your body is burning fat and carbs as energy sources, as well as what foods are most appropriate for you and your goals, using the personalized nutrition plan it provides.

Without going into a lot of detail, essentially each time you take a measurement by breathing through the Lumen (as guided by instructions in the Lumen app), you are given a score of 1-5 on a scale from 1 (burning fats) through 5 (burning carbs).

The principle is if you can get into that fat burning zone of 1 or 2, then you’ll be less reliant on using carbs as fuel, and also burning fat that you’re carrying around in your body.

Assuming you set your goals as being weight loss-focused when you set up your Lumen profile, then the food nutrition plan Lumen will provide you with will be focused on helping you achieve that goal.

Does Lumen really work?

The effectiveness of whether Lumen really works in achieving the goals of helping users improve their metabolism and lose weight by measuring their breath and providing personalized nutrition recommendations is certainly a topic of debate.

I certainly believe it works if you stick to the recommendations and are consistent with your measurements. Don’t give up on it too soon, as with most things in life, patience is a virtue when it comes to seeing fitness and health results.

While Lumen has some scientific basis in terms of measuring breath to assess metabolic rate, there is limited research on the device itself and its efficacy in promoting weight loss.

As I said before, I believe it depends on the user and their ability to stick to the process, rather than giving up too soon.

Some studies suggest that measuring breath can be a useful tool for weight management, but more research is needed to determine the long-term effectiveness of Lumen in particular, all of which I’m sure the company is gathering with its rather large user base.

It is important to note that any weight loss device or program should be used in conjunction with a healthy diet and regular cardiovascular exercise like running or cycling.

Lumen is not a magic solution for weight loss, and users should not rely solely on the device to achieve their weight loss goals.

Consultation with a healthcare professional is always recommended before beginning any weight loss program.

Why track your metabolism?

The most popular reasons for knowing how to measure your metabolism include targeting healthy weight loss, enhancing how and when you burn fat or carbs when working out or in general throughout the day, and boosting your energy levels through optimized nutrition planning.

What is metabolic flexibility?

Before I explain how using Lumen can help with weight loss, let’s first go over a term you’ll see mentioned by Lumen on their website: Metabolic Flexibility.

Metabolic flexibility is essentially your body’s ability to efficiently switch between using carbs or fat as its main source of energy.

This is important because it places a focus on training your body to use the food you eat as fuel.

This means that as you improve your metabolic flexibility, your body learns to burn the most appropriate fuel source.

Metabolic flexibility can help you lose weight (when you may want to burn fat as the main source of energy), as well as maintain weight and energy levels, in which case you may be more focused on ensuring you’re consuming enough carbs to have them available to your body as an energy source.

You know the saying, that someone has a good or great metabolism? What does that really mean?

Well, often it means that this person has good metabolic flexibility, and is therefore efficient at using fat as an energy source, and switching between burning carbs and fat when their body is depleted of carbs.

This can mean they’re less likely to store fat, and less likely to crave carb-laden foods, so are typically unlikely to be overweight.

Wouldn’t it be nice if we could teach our bodies to do this, and support our body in this way by knowing what is best to eat, and when – with no ‘diets’ involved? This is what using Lumen can help you achieve by giving you the information and guidance needed to do this, sustainably.

This can help demystify why you think you’re eating all the right things and making the right moves, but still don’t manage to lose weight (if that’s your goal).

Lumen key features

The stand-out key features of the Lumen system are how simple and pleasant the device itself is to use, and how clear and informative the readouts and nutrition plans are, that are provided through the app.

The Lumen device has a very attractive design.
The Lumen device has a very attractive design.

Lumen’s personalized daily nutrition plans

If you’re looking for recommendations on what to eat each day, including breakfast, lunch and dinner, then you can use the Lumen app to customize the meal inspiration it provides you with (e.g. you can select what you do/don’t can/can’t eat).

It will then provide you with recommendations for daily carbs, fat and protein servings, as well as recipes that meet these criteria and plenty of information explaining serving sizes and what specific foods would meet the carb/protein/fat and service size criteria.

Lumen review nutrition screenshot trail and kale
On this day I’m recommended to have 8 carb servings.

What’s also great about the nutrition aspect of the app is the information it shares to help educate yourself on what is best to eat, when, and – importantly – WHY!

Learning from this information and experience will ultimately make you more self-sufficient and knowledgeable about the effects of what you choose to eat and drink throughout your day.

Food logging function

Lumen also offers the ability to log the foods you eat throughout the day.

Although this isn’t a feature I use, it’s proven to be highly popular with other Lumen users, who can now track their macros all in the Lumen app, without having to log into other apps such as MyFitnessPal to track this information.

It includes the ability to add custom foods and track based on servings or measurements (eg. grams).

For people located in the US and Canada, it offers a barcode-scanning function, so you can scan the barcodes of bought food and automatically add them to your food log.

Suggested meals

The meal plan information it provides is targeted at encouraging your body to get into that fat-burning zone that is so important for enabling efficient, sustainable weight loss.

As someone who prefers to eat plant-based, I did, however, find the suggested meal plans very heavy on the tofu/seitan spectrum (I’m not a fan of either of these and prefer to eat whole foods), and the non-meat recipes are kind of complicated.

For example, it requires another level of commitment to prepare and eat recipes such as ‘scrambled tofu and a spinach salad with chickpeas and peas’… for breakfast).

Hopefully, with further development, simpler meal suggestions will be included.

The Lumen Flex score

Lumen Metabolism Tracker Review Trail and Kale web wm 8
Pinky finger up is optional when breathing through the Lumen 😉

Each week, after regular use of the device first thing in the morning (as well as at other times of day, such as before and after meals and exercise), you will be presented with your ‘flex’ score, which rates how flexible your metabolism is out of a maximum of 21.

The goal for many people will be to work to increase the Lumen flex score, so your body becomes more efficient at switching between burning fat and burning carbs throughout the day and night.

Integrations with third-party fitness trackers

As well as being easy to connect to the iPhone (or Android) app each time you use it, you can also connect your Lumen app to your fitness tracker or running watch. That includes Apple Health and Garmin running watches, which we frequently use here at Trail & Kale HQ.

Lumen review measurement screenshot trail and kale
An intensive 30 minute HIIT cycle put me to a level 2/5 (fat burning mode!).

The app from Lumen measures when you have been exercising and will provide you with the opportunity to add your workouts to your app, so you can easily see the effect of your exercise on the Lumen measurements, and get prompted to measure your metabolism before and after workouts.

What’s included when you sign up to Lumen?

With your Lumen sign-up you get full access to all of the Lumen app features, nutrition and meal planners, exercise logs and advice. Additionally, you get your Lumen breathalyzer device.

It’s compact, feels solid and high quality, with a soft glowing purple indicator circle light, a soft on-off button, and a metal protective cap over the end you breathe into.

It has been designed to be small enough to easily fit in the palm of your hand as well as take on the go with you. It will fit in most pockets, and easily stows inside a small handbag.

It has been designed to be small enough to easily fit in the palm of your hand as well as take on the go with you. It will fit in most pockets, and easily stows inside a small handbag.
It has been designed to be small enough to easily fit in the palm of your hand as well as take on the go with you. It will fit in most pockets, and easily stows inside a small handbag.

It comes with a charging stand and travel case so it’s easy to keep next to your phone by your bed, as well as placing in a pocket if you’re on-the-go and need to track your metabolism throughout the day.

There’s plenty of battery life for multiple days without charging, and its charging stand is minimal and unobstructed, whether you choose to keep it on your nightstand or in the bathroom.

The charging stand is minimal and unobstructed, whether you choose to keep it on your nightstand or in the bathroom.
The charging stand is minimal and unobstructed, whether you choose to keep it on your nightstand or in the bathroom.

My experience using the Lumen metabolism tracker

Having used the Lumen metabolism tracker regularly for a couple of months, I have been able to gather so many insights about how and when my body is burning carbs vs burning fat as fuel. But more than this, I find the tips and personal nutrition planner helpful in informing, or at least validating, my meal choices throughout the days and weeks.

It’s been a very helpful reminder, for example, that eating more protein and less carbs on some days encourages your body to deplete its carb stores and switch to use fat as its main source of fuel – and this is something that’s important to get in the habit of to train your body to use fat sources efficiently.

Eating more protein, and boosting metabolism through lifting heavy weights and high-intensity interval training are the three key ways I know to get myself into that fat-burning zone (as supported by articles such as this one from Harvard Medical School).

As an endurance runner, being able to tap into fat as a fuel is so important to be able to keep moving on long marathons and ultramarathon efforts, as well as supporting weight loss, if that’s a goal. Without the ability to do this, once you run out of carbs as an energy source, then those long runs can become very slow and painful!

An unexpected benefit of signing up for Lumen is also the community of other users and Lumen staff that you’ll find support in through their private Facebook community.

It’s a great place for Lumen users to share their stories and also ask questions to learn about the device and how to get the most out of tracking your metabolism to support weight loss or other metabolic health and fitness goals.

We have never been a fan of dieting, whether that’s elimination diets or fasting, as that doesn’t align with our views on what eating and living healthily means.

With Lumen, you don’t need to fast for multiple days (although overnight fasts are encouraged), and you don’t need to do any aggressive diets or follow plans such as Keto.

It’s a tool, guidance and meal planning device that allows you to be more thoughtful in what you’re choosing to eat, and when, and how that will affect how your body sources its energy.

It provides real data and insights into what’s going on in your body, and when it’s ok or less beneficial to eat carbs, for example.

Lumen Metabolism Tracker Review Trail and Kale web wm 9

Ultimately, if you’re looking to lose weight or have other metabolic health and fitness goals that relate to how you fuel your body, then take a look at Lumen. Knowledge is power, and this little breathalyzer device empowers you to learn about your body and train its metabolism to work efficiently.

This includes supporting your journey to lose weight, improved energy level and overall health benefits as a result of eating appropriate food at a suitable time of day based on your current metabolic state.

Additionally, because of all the features in the clean, easy-to-use app, you can replace your existing meal/calorie tracking apps, and do the logging directly into Lumen, which is a more powerful tool given all the additional information it provides you with.

Cost and where to buy

To use Lumen choose between three plans: 6, 12 or 18 months. The best value (and most popular) option is the 12-month plan, which costs $299 for the year (and can be renewed or canceled after that time). The device itself is free – you get it sent to you, included within that price.

After purchasing the Lumen metabolism tracker, you gain access to Lumen’s Facebook community group which has over 19,000 members already, a testament to the popularity of this weight-loss, and metabolism booster tool.

In the group you can ask questions, hear other users’ success stories about their journey to lose weight, and generally get tons of motivation for your own metabolism control, or weight-loss journey.

When you consider this works out to less than $25 a month for all this information and support, this is a great deal – and that’s before you apply our exclusive 15% off discount code – TK15 – that takes it down to around $21/month 🙂

The button below will take you to Lumen’s website and a comparison between the three plans – and don’t forget to use the TK15 code at checkout if you go ahead and order one for yourself:

Lumen Review summary


One of Trail & Kale's co-founders, a mom, and guardian of our resident trail dog, Kepler, Helen can be found trail running with Kepler and enjoying road runs with her mini in a jogging stroller, all while testing out the latest running gear for our readers.



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