Lumen review UK: I tried the Lumen metabolism tracker — it’s a great tool for fat loss
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MY work as a nutrition coach and personal trainer means I like to keep up to date with all things diet and fitness, and I’m passionate about health and exercise.
The recent growth in popularity of fitness devices like Lumen is an exciting development and has added a whole new dimension to the concept of healthy living, enabling users to track their metabolic health and adjust what they eat accordingly.
Simply breath into the tracker – so you exhale into the device – and Lumen will tell you if you’re using carbohydrates for energy, or if your body is in fat-burning mode at any given time. Using this information it will then devise an eating plan for you for that day.
There are lots of case studies showing how well Lumen works, but I wanted to see for myself what the hype was all about and whether the device and associated app could deliver on its promises.
I tried Lumen for six weeks and followed its recommendations – read on for my thoughts.
Lumen metabolic tracking device, £199 including one-month's free subscription (then £19 per month)
Pros
- 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
Cons
- Pricey
- It WILL tell you to eat fewer carbs
- Time-consuming: you need to use it fairly frequently for the best results
Rating: 4.5/5
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.
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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.
Lumen metabolic tracking device, £199 including one-month's free subscription (then £19 per month)
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 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.
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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 any 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, and then sends the data to an app, which uses your measurement and several algorithms to report if you are using fats or carbs for energy.
The device works by detecting the levels of carbon dioxide (CO2) 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. You aim 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.
Lumen metabolic tracking device, £199 including one-month's free subscription (then £19 per month)
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.
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.
Lumen metabolic tracking device, £199 including one-month's free subscription (then £19 per month)
Lumen UK review: final 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.
How long does it take to see results with Lumen?
Lumen focuses on improving your metabolic flexibility – your ability to move back and forth between burning carbs and burning fat.
The device shows your current measurements from the first time you use it. Ideally you want to be showing a score of 1 or 2 when you take your first measurement of the day after waking as this shows you’ve burned carbs and are now burning fat. After eating your score should be 4 or 5, which indicates your body is burning the carbs from your food.
After two weeks Lumen gives you a flex score 1 – 21, showing how flexible your metabolism is and you should be aiming to increase this score over time. Your flex score then updates weekly and the longer you use the device and stick to the nutritional recommendations the more your metabolic flexibility should increase.
Where to buy Lumen in the UK
At the moment the only place you can purchase the metabolism tracker is through , 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 out of the tracker.
How much does Lumen cost?
At the time of writing, you can expect to pay £199 for the device and one free month of membership.
Once your first month expires, the cost is £19 each month for use of the app, or save 30% with an annual membership, which works out at £13.25 per month.
You can save another £25 by
Can I use the Lumen metabolism tracker without a subscription?
Yes you can if you purchased your Lumen after 30 July 2023, however you will not be able to access personalised insights, guidance or the Lumen membership experience.
Using the tracker without a subscription will only allow you to get your Lumen level and to take metabolic measurements
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 misinterpreted.
So if you want to share your device with a friend or family member they'll need to sign up for their account on their smartphone.
What are the alternatives to Lumen?
There are several 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?
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.
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 $19.99 per month so around £15 monthly (or $79.99 if you pay annually).
Other weight loss and fitness tracker apps include , , and .
Is Lumen legit?
Lumen is 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. Impressed with the app and how much of a focus there is on having a relaxed attitude to measuring macros.”
Can Lumen detect ketosis?
The short answer to this is no. Lumen does not detect or measure ketones in your body, rather it provides an individual and personalised eating plan depending on the needs of your body, to eat more – or fewer – carbs and fats on any given day.
Lumen measures CO2 and can determine whether your body is burning carbs or fat, but it won’t point out that you’re in ketosis, even if you are.
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Ketogenic diets are now incredibly popular, but this way of eating demands very low carb intake with increased fat and protein intake. Long-term, this diet proves unsustainable for many and even if it works for you, once off keto there’s a real risk of regaining weight if you don’t increase your carbs gradually.
Lumen provides a nutritionally balanced eating plan based on whether your body needs more carbs, or more fat, which is sustainable long-term.