Lumen review UK: what is the metabolism tracker and does it work? | The Sun

Lumen review UK: what is the metabolism tracker and does it work? | The Sun

June 6, 2023

AS a personal trainer and qualified PN1 nutrition coach, I jumped at the chance to review the Lumen fitness tracker.

I’m passionate about health and fitness – and I know my onions when it comes to diet and exercise. I was super excited for my Lumen review and eager to discover if it would work for me.

I’d seen the adverts, promising that it would “hack my metabolism”, and case studies showing how Lumen has helped people to improve their energy levels, fitness and strength, as well as helping with weight loss and encouraging healthy eating.

But I wanted to know for myself: does Lumen work? I tried Lumen for six weeks to see if the breathalyser device and associated app can really deliver on any of these promises…

  • Lumen metabolic tracking device, from £249 for 3 months – buy here

Rating: 4.5/5


  • Holds you accountable
  • Realtime feedback about your metabolism
  • Good recipe ideas
  • Promotes long-term health benefits, not just weight loss
  • Very quick and efficient customer support


  • Pricey
  • It WILL tell you to eat fewer carbs
  • Time-consuming: you need to use it fairly frequently for the best results

Lumen review: quick summary

In short, I mostly enjoyed using the Lumen and found the insights provided by the connected app to be very interesting, particularly the ones concerning whether or not I needed to eat before training.

The answer was often ‘no’, so I found myself fasting for longer periods after waking up and despite not always following the daily nutrition plan (and going over the recommended amount of carbs) I noticed some weight loss due to generally just eating less than usual and having my carb-heavy meals earlier in the day.

Essentially, what you use the Lumen device for is measuring your breath first thing in the morning, around every meal, before and after exercise and right before bed. You can also do ad hoc measurements throughout the day if you feel the need; you then receive feedback via the connected app as to whether you are burning carbs, fats or a mixture of both.

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Credit: Lumen

It uses this information to devise a nutrition plan each morning, telling you if it’s a low or high-carb day. If you’re willing to follow the plan, which can be tough on low-carb days, you will see results, whether that be weight loss, weight maintenance or just understanding and improving your “metabolic flexibility”.

This emphasis on improving metabolic flexibility is what Lumen is all about. The term describes the body’s ability to flit easily between burning fats and carbs, using energy from the best suited macronutrient depending on the body’s needs.

The Lumen promises to teach your body to use fat and carbs at the correct times, which in turn aids fat loss and weight maintenance. The aim is to wake up each day in a state of fat burn, and you really do have to watch what you eat the day before to make sure that happens.

In that sense the Lumen is good at holding you accountable: it does feel like it knows if you don’t follow the plan! It’s a fresh alternative to calorie-restricted diets, so I would say it’s worth a try, especially as there’s a 30-day free trial on offer. You can save another £25 by signing up for the newsletter.

  • Buy a Lumen with subscription from £249 – here


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Lumen review: full review

What is Lumen?

Lumen is a device that you breathe into to discover if your body is using fats or carbs for energy at that given moment. 

After measuring several breaths a day, the connected app can devise a nutritional plan to improve your ‘metabolic flexibility ’ – this is your body’s ability to swap between carbs and fats and use the correct energy source at the most effective time. 

This is useful because it helps increase your energy levels, it can improve your quality of sleep and if your goal is weight loss, it can help with this, too, by encouraging your body to tuck into those difficult-to-access fat stores.

How does Lumen work?

It can be quite complicated to get your head around, but every purchase of a Lumen comes with a 30-minute onboarding video call with a Lumen expert to get you started. 

The Lumen itself is a smart tube-shaped breathalyser that collects your breath, then sends the data to an app, which uses your measurement and a number of algorithms to report if you are using fats or carbs for energy. 

The device works by detecting the levels of Carbon Dioxide (CO2) that you are breathing out – if it’s a high level of CO2, it means you’re burning carbs; if it’s low, you’re burning fat. You’ll also get measurements in between. 

Lumen works using a five number spectrum. A marker of ‘1’ means you’re burning fats; ‘2’ is ‘mostly’ fats; ‘3’ is a mixture of the two macronutrients; ‘4’ is ‘mostly’ carbs; and ‘5’ is carbs. 

Lumen says that for optimal health, you want to be measuring 1 or 2 when you wake up – this means your body is good at burning carbs overnight while you’re sleeping and has now turned to burn your fat stores. Ideally, you want a 4 or 5 after meals as it shows that your body is using up the carbs you’ve just eaten. 

Before you start your Lumen journey, the app asks you to choose your ‘track’ so it can determine your goals. You can choose from ‘Metabolic Health’, which is to improve your general health and metabolic flexibility, ‘Healthy Weight Loss’ and ‘Fitness Performance’ the latter of which is more based on nutrition to improve your workout. I trialled the weight loss option, as this is the most popular with Lumen users.

Every morning, after you’ve taken your measurement, the app gives you a nutritional plan telling you how much carbs, protein and fat to eat that day. The recommendations are dependent on your breath that morning, the exercise you’re planning to do that day (you need to enter this into the app) and data from the day before. 

Some days the amount of carbs can be as low as four portions (60g of carbs) which is the equivalent of a banana, two pieces of bread and a cup of milk. However, the app does provide recipes to make those carbs go further and a food checker and food charts showing how many carbs are in different foods (and will soon be adding a food logging system). 

After two weeks of using Lumen, you’re given a ‘flex score’ of between 1 and 21 depending on how flexible your metabolism is, with 1 being the lowest. Your aim is to progress to a higher number as the weeks pass. 

The nutritional plan aims to improve this score: the higher the score, the better your body has become at using the right energy source and the better your health will be.

Is Lumen easy to use?

I struggled a little bit with the breathing element at first, but after a couple of weeks, I managed to get it right. You have to hold the Lumen to your mouth and take a slow, deep breath in, hold it for 10 seconds (the app counts down) and then breathe back into the Lumen nice and slowly – you have to do this between one and three times for the Lumen to get enough data. 

To start with, I did this first thing every morning, after I finished my morning fast (fasting is very much encouraged by Lumen), before and after every meal, before and after exercise and again before bed, so I was using it eight or nine times a day. 

Over the weeks I started finding this time-consuming and just a bit annoying, so I went down to five or six times a day, which was still enough to get good data. The app is straightforward to navigate and has lots of advice and recipes that help you stick with your recommended carb, protein and fat intake for the day. 

I decided to follow just the carb recommendations to start (to keep things less complicated) and I did struggle with the low recommendations. Still, the app does up the recommendation if you exercise, so it inadvertently encourages you to work out. 

The recipes are based on the food preferences you add in, with chicken, fish and vegetable dishes cooked in innovative ways, and the app has lots of videos and blogs to answer any questions. There’s also direct access to customer support who are very quick to respond. I had an issue with the Lumen not working properly and they replied instantly with a fix.

How much does Lumen cost?

The Lumen comes in packages that include access to the integrated app for different periods of time. At the time of writing, you can expect to pay £249 for the device and 3 months of tracking (use of the app), £299 for 6 months or £349 for 12 months.

Once your paid-for months expire, the cost is £25 a month for use of the app – the device is basically useless without the app as you won’t get any readings, insights or nutritional plans.

You can save another £25 by signing up for the newsletter first.

Does Lumen help you lose weight?

Yes, I think it does, but you have to know what your goal is and be determined to “trust the process”, a saying that gets used a lot on the Lumen community Facebook page. 

I opted for the weight loss ‘track’ and did struggle to stick with the fairly low calorie and carb count as I love my pasta and potatoes. I frequently went slightly over the recommended carbs but still lost weight and managed to see an improvement in my ‘flex score’. I think one of the reasons for the weight loss was the intermittent fasting that Lumen encourages, so I was probably eating fewer calories than usual overall. 

I also followed Lumen’s advice to eat dinner a bit earlier and have my carb-heavy meals earlier in the day. All this helps you reach that 1 or 2 flex score goal first thing the next morning. 

What are the alternatives to Lumen?

There are a number of health and fitness apps and trackers on the market that offer a variety of options when it comes to monitoring your diet and exercise levels.

They all work slightly differently so it’s worth knowing what you want to achieve before researching possible solutions – are you after weight loss, increasing your fitness levels or simply all-round better health?

Noom is a subscription-based weight loss app with an emphasis on changing behavioural patterns with eating and exercise. It's a 4-month subscription costing £33.60 per month.

To sign up for a plan, you take a quick survey, answering questions about your weight loss experience and goals.

MyFitnessPal is a similar weight loss and fitness site and app with a calorie tracker. It includes a database of 14 million foods so it's easy to track your calorie intake using the barcode scanner or by manually searching.

The free version is quite limited but there is a free trial of the premium version, which you can customise and tailor to your personal health goals. The premium version costs $20 per month so around £15 monthly.

Other weight loss and fitness tracker apps include Fiit, Fitbit, Strava, Nike Run Club and WW.

Is Lumen legit?

Lumen is definitely legit and its supporters swear it works. It takes input from you, but then you need to be committed if you want to make a difference and improve your health. Lumen has more than 1,000 reviews on Trustpilot – and more than 75% of these are five-star.

Comments from enthusiastic fans include: “Lumen has opened my eyes regarding how my metabolism works. The support and resources are amazing,” and “A great device for achieving balance and health. Really impressed with the app and how much of a focus there is on having a relaxed attitude to measuring macros.”

Lumen UK review: the verdict

The best thing about Lumen is the accountability – it’s the modern-day version of having a Weight Watchers team leader following you around!

If you want to achieve that score of 1 or 2 the next morning, you really do have to follow the nutrition plan the day before, and having a daily goal like that does make you try harder to eat healthily (there’s no room for snacking on biscuits or crisps on this plan).
The low-carb days also make you want to work out as this ups your carb allowance, which is a great incentive.

Overall, I think Lumen is a good tool to action weight loss if that’s your short-term goal but then it’s also there for a long-term goal of being a healthier person in general.

I enjoyed using it before workouts to determine if I needed to eat beforehand, and the advice was accurate when it said I still had enough fuel to run 15km without breakfast. I’m going to keep using the Lumen past the trial but I have moved my track to the fitness setting to see how it can impact my performance.

  • Lumen with 3-month subscription, £249 – buy here

Where to buy Lumen in the UK

At the moment the only place you can purchase the metabolism tracker is through Lumen's website, where you can sign up for the Track subscription.

Technically, the device comes 'free' with the Track subscription, which is what you are paying for to get the most of the tracker.

How much does the Lumen cost?

The range starts from £249, with three tracking options over three months to a year, but you can make savings by option for longer plans and for signing up to Lumen's newsletter.

Here are all the plans you can choose from;

  • Metabolism Reset, 3 months Track for £249
  • Metabolism Booster, 6 months Track for £299 (save £90)
  • Metabolism Optimizer, 12 months Track for £349 (save £150

There is also a nifty little saving of £25 off your order if you sign up to Lumen's newsletter.

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Can two people share one Lumen device?

As Lumen is only usable by one person per app, you won't be able to share it on one account, as the data would be misinterpred.

So if you want to share your device with a friend or family member they'll need to sign up for their own account on their smartphone.

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