Lumen review: boost metabolism, improve mood and sleep with this Chris Froome-endorsed device

Lumen review: Not a silver bullet for weight loss but Lumen can certainly improve mood, energy levels and general wellbeing

Lumen review
(Image credit: Lumen)
T3 Verdict

Neither is it cheap, nor is it the ultimate solution for weight loss, but when used correctly, the Lumen metabolism tracker and the dietary recommendations in the Lumen App can help people manage energy levels more efficiently and even improve mood and sleep.

Reasons to buy
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    Easy to use

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    Food recommendations are great

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    Can improve general wellbeing

Reasons to avoid
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    Can't track macros straight into the Lumen App

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    Lumen Fex Score is not enough gamification to keep users engaged on the long run

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Lumen review TL;DR: Not a silver bullet for weight loss but Lumen can certainly improve mood, energy levels and general wellbeing. As long as you put some effort in.

Admittedly, advertising Lumen as a device that will ‘hack your metabolism’ is a bit misleading. This statement might give people the idea that using Lumen, which is essentially a special type of breathalyser, will change their metabolism quickly and supercharge their weight loss journey instantly. This is not true.

However, Lumen can be a powerful metabolism controlling device when used correctly, even if the user isn’t planning on losing any weight. Most people could benefit from the body being capable of switching from one energy source to the other quickly and efficiently when needed. But how can this be achieved and how does Lumen work? Let’s find out.

Lumen: price and availability

Lumen is available now for a recommended retail price of £349/ $350. Lumen can be purchased directly from Lumen and at selected third party retailers.

Lumen review

(Image credit: Lumen)

Lumen review: what’s Lumen and how does it work

Lumen is a hand-held, portable device that measures metabolism. In essence, Lumen is a breathalyser that uses “CO2 sensor and flow meter to determine the CO2 concentration in a single breath.” Based on this, the Lumen App can determine what type of ‘fuel’ your body is using at any given point: carbs or fat.

Why does it all matter and why would anyone need to measure metabolism? I was genuinely surprised how badly Lumen (the company) explains this on its website. Although the main marketing campaign focuses on the breath measurements, it’s only half the battle. If users want to see progress, they will also have to follow the diet suggestions in the Lumen App.

These recommendations are based on macronutrients, or macros for short, a daily mix of carbs, fat and protein. As well as taking ‘breath-readings’ frequently, users will have to adhere to the recommended macro mix each day to achieve the desired result. This result being a ‘flexible metabolism’.

What is flexible metabolism? A flexible metabolism can shift from using carbs to using fats for fuel easier, balancing energy levels more effectively. Should the diet recommendations be followed, in theory, Lumen users can avoid ‘energy dips’ during the day and generally feel more focused.

Sounds too good to be true? Based on my experience, it is more than achievable, even after using Lumen for a couple of weeks only. Needless to say, it requires some will power to change your diet significantly and go from a high-carb to high fat/low carb diet but it’s totally worth it.

Lumen review

(Image credit: Lumen)

Lumen review: how should you use Lumen

It takes roughly a week of frequent breath measurements to determine the user’s ‘breath signature’ and four weeks to be given a Lumen Flex Score. The former is required for more accurate measurements and admittedly, it takes a bit of an effort and dedication to achieve. To ‘teach’ Lumen, users have to measure breaths fairly often throughout the day and also track carb consumption.

Initially, the best (and fastest) results are achieved by taking measurements before and after meals and workouts to help Lumen understand how the body reacts to these. This also means that tracking macro intake is required which can admittedly be a bit challenging to some. Not only the best way to keep track of macros is to ‘meal prep’ (cook for yourself ahead of time) but people also need to keep track of when they eat these meals..

The most important time to measure breath is the mornings. I found the most optimal time to take the morning measurements is just before breakfast, before the overnight fast is broken. Taking a measurement right after sleep might skew the reading  – apparently, the body burns carbs for a bit after you wake up – plus fasting for longer might help ‘empty out the carb stores’ even more.

After the first four weeks, Lumen users are given their ‘Lumen Flex Score’ (LFS). This represents metabolic flexibility (how efficiently the body switches between macros to fuel itself) and ranges from 0-21. 0-6 represents low flexibility, 7-14 medium flexibility and 15-21 high flexibility. The higher the LFS, the better, and Lumen also explains the score further in the app and in the weekly update email.

Lumen review

(Image credit: Lumen)

Lumen review: the Lumen App

The Lumen App acts as a command centre for achieving metabolic flexibility. The portable Lumen device might take measurements but these are all assessed in the Lumen App and dietary recommendations are also communicated here. The aforementioned Lumen Flex Score is displayed in the Lumen App too.

Navigating the app is easy. Until the morning measurement is taken, most of the home screen is taken up by the reminder to take this measurement and dietary recommendations are only offered after the morning breath was analysed. People might get confused by the ‘carb servings’ recommendations at first but in reality, it’s straightforward: one carb serving is 15 grams of carbs. That’s roughly half a banana or approx. 20 grams of rice.

Considering the standard Western diet, most people will be offered a high fat, low carb diet initially until their ‘carb stores are emptied’. Once this done, the Lumen App will recommend a mixture of high fat and high carb days, based on the morning measurements and the number of carb servings users had the day prior to the reading.

In the Lumen App, users can also check nutritional info on ingredients, get food recommendations and even see ‘personalised’ insights which are very generic but provide additional information about the process and dietary advice.

As for third-party app support, the Lumen App works with Google Fit (it was trialled using an Android phone) and also has a dedicated widget in the Garmin Connect IQ store. A Lumen widget can be added to supported Garmin watches, such as the Garmin Fenix 6 Pro, to receive breath reminders after workouts.

Lumen review

(Image credit: Lumen)

Lumen review: my Lumen experience

For someone who is generally interested in nutrition, using the Lumen was a great experience for me, but even I agree it’s not for everyone. I don’t have to cook for a family of seven every day and also work from home so it was easy for me to follow the nutrition guidelines. To track macros, I used the free MyFitnessPal app: it would definitely be more convenient to track macros in the Lumen App so it would know in the morning how many carb servings you had the day before automatically.

Using the hand-help breath analyser is not a complicated ordeal. There is only one button on the device, you press it while the app instructs you to do so, inhale through it, hold the breath for 10 seconds, exhale through it again and repeat the process 2-3 times each time. Holding the breath for 10 seconds was an alien experience at the beginning and I can see some people struggling with it, especially people who smoke.

After following the diet for a few weeks, I noticed that my energy levels were more stable throughout the day and I didn’t experience the usual post-lunch energy dip either. Taking measurements every morning became a habit but I must admit that after using Lumen for a month, I was taking measurements less and less frequently. However, as long as the carb intake is logged every day and the morning measurements are taken, the app should be able to recommend the right diet.

Talking about diet: the Lumen App does have a food recommendation system, in case someone needs a bit of inspiration. Food ideas are grouped around the number of carb servings they contain and better still, the app provides at least a few alternatives for each ingredient. All recipes can be filtered too based on ingredients.

Lumen review

(Image credit: Lumen)

Lumen review: verdict

I thoroughly enjoyed using Lumen but I must admit, it’s not for everyone. For people who struggle with adhering to their diet and managing their energy levels, Lumen can be a heaven sent. For others, people with a hectic lifestyle and those who prefer not to cook for themselves, using Lumen might not make that much of a difference.

Lumen only works if you put the effort in but if that’s the case, you will see improvements soon enough, after a couple of weeks. Not saying it will work for everyone and unfortunately it is not cheap either. That said, the app itself is free and there is no extra charge for the service either so getting a Lumen is a one-off cost, unlike getting a Peloton bike where you have to pay loads for the bike plus even more to access the workout library each month.

Should you get Lumen? If you are happy to work for your goals, definitely. It is not a perfect solution to lose or to gain weight but using Lumen can make the difference for the dedicated. As long as you keep on using it.

Get Fit for 2021!

This is part of T3's Fit for 2021 programme, which will be running throughout January. We aim to bring you tips on diet, lifestyle and exercise that will help you shape up for what is certain to be a difficult year. One thing we can guarantee: it WILL be better than last year. And hopefully we'll help you get the most out of it. 

Matt Kollat
Section Editor | Active

Matt Kollat is a journalist and content creator who works for and its magazine counterpart as an Active Editor. His areas of expertise include wearables, drones, fitness equipment, nutrition and outdoor gear. He joined T3 in 2019. His byline appears in several publications, including Techradar and Fit&Well, and more. Matt also collaborated with other content creators (e.g. Garage Gym Reviews) and judged many awards, such as the European Specialist Sports Nutrition Alliance's ESSNawards. When he isn't working out, running or cycling, you'll find him roaming the countryside and trying out new podcasting and content creation equipment.