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An Up-Close And Personal Look At The Lumen Metabolism Tracker [A Review]

lumen metabolism tracker review

The Lumen Metabolism Tracker is a small device that might remind you a little of a breathalyzer, but instead of telling you whether you’re safe to drive or not, it gives you an idea of what type of fuel your body is burning for energy.

The idea behind it being that if you know what your body is using for energy, you can use that info to help you adjust your eating habits in order to reach goals like losing weight, improving athletic performance, improving energy levels, etc.

I’ve gotta be honest- I’ve never heard of a metabolism tracker before, but when the good people at Lumen offered to send me one to try out, I figured (if nothing else) it would be educational.

And after using the Lumen Metabolism Tracker for a week, I can confidently say that it has indeed been educational.

If you’re thinking about buying the Lumen, keep reading. I’ll go over everything you need to know, as well as how my hands-on experience with the device went.

After reading, you’ll have a great idea as to whether or not this spiffy looking machine is worth investing in.

Disclaimer: Lumen sent me their Metabolism Tracker to try out and review. I haven’t been compensated in any other way. My review is based 100% on my experience using the device. 

The Lumen Metabolism Tracker

Lumen reached out to me to see if I’d join their affiliate program a while back. I briefly checked it out, thought it looked kinda interesting, and decided to sign up for their program.

Then I kinda forgot all about it and when along with my everyday business.

Well, a few months went by and Lumen reached out again seeing if I’d like to try one out first hand for a review.

Seeing as I had forgotten about signing up for the program to begin with, I had to look Lumen up again to see what this “metabolism tracker” was again.

And, to be brutally honest, I thought it sounded cool but kinda looked like a waste of time- but hey, if they’re willing to send me one, why not try it out right?

Well, long-story-short, I’m glad I decided to give it a go because I think the Lumen is pretty awesome. It’s easy to use and I find the information it provides helpful.

But before we dive-in too deep, I want to back up a little and make sure everybody knows what this thing is supposed to do in the first place.


  • Gives you a measurement based on how many carbs your body is burning
  • Easy to set up
  • Easy to use
  • Personalized daily diet plans based on macronutrients and your goals
  • Great app
  • Informational guides, meal ideas, serving suggestions
  • Long lasting battery
  • Sleek design
  • Fair price
  • 30 day money back guarantee
  • 1 year warranty


  • Difficult to cross reference how accurate readings are

How Does The Lumen Work?

Ok, so the Lumen is a metabolism tracker, which means that this little device is designed to tell you what your body is burning (or metabolizing ) for energy.

Our bodies have 3 potential sources of energy: carbohydrates, fat, and in extreme circumstances (like starvation), protein.

Our bodies don’t like to burn protein for energy, and as long as you’re eating regularly, it’s rare that your body would have to burn much protein for fuel- but if you’re not eating regularly, or fasting for long periods, your body can burn the proteins found in skeletal muscle as a source of energy (resulting in loss of muscle mass).

But most of us will be burning a combination of carbs and fats throughout the day.

And the Lumen can give you an idea as to how much carbs or fat your body is currently burning when you use it.

Why would you want to know what fuel source your body is using? That’s a fair question- and one I’m not sure I could’ve sufficiently answered before using this device.

But now I know this info can be very helpful for people trying to lose weight. In order for us to lose weight, we have to get our bodies to burn fat (which is literally stored calories).

Our bodies want to burn carbohydrates for fuel when there’s an ample supply of them floating around in the blood stream. In order to transition our bodies into a state of fat burning, we need to control the amount of carbs in our system.

There are different ways of doing this, primarily through diet and exercise.

Eating fewer carbs to begin with will quicken the transition from burning carbs to fat. Exercising will cause your body to burn those carbs in your system faster, which can lead to the transition to fat burning as well.

Realistically, our metabolisms are a lot more complicated than this and our bodies are continually burning changing combinations of carbs and fats throughout the day.

But for the sake of simplicity, this is more or less how it works.

So, the idea is that if you know what type of fuel your body is burning, you can adjust your eating and exercise habits around it to maximize your gains.

And this is exactly what the Lumen does.

The Lumen rates your body’s metabolic activity on a scale from 1 to 5, with 1 meaning your body is burning almost entirely fats and 5 meaning your body is burning mostly carbs (and 3 being a fairly equal combination of the 2).

Based on this information, you adjust your daily intake of carbs, fats, and protein.

Oh, I should’ve probably mentioned that the Lumen works by measuring the O2 and CO2 concentrations in your breath- you inhale fully through the device, hold your breath for 10 sec, and then do a controlled exhale through the device.

You have to do 2-3 breaths for each measurement and it takes a little practice to get it right. The app does a nice job of coaching you through it and they use some helpful visual aides to make sure you get the breaths right.

I’m not going to pretend I know all the science behind how the Lumen can determine what your metabolism is doing based on the CO2 concentrations in your breath, after all, it’s been a loooong time since my exercise physiology course.

All I can say is that this device is able to estimate your respiratory quotient (RQ) based on the percentage of CO2 your body uses when compared to the room air you inhale.

Having more CO2 present in your exhale is indicative of more carbs being burned; less CO2 indicates more fat being burned.

The science behind this method has been around for a long time- but you had to go to an exercise physiology lab for more advanced testing to get the results.

Lumen puts this technology in the palm of your hand, where you can use it in the comfort of your home.

So, Lumen advises you to test your breath each morning before you eat. This is a time that most of us have been fasting for an extended period (as we sleep) and it gives you an idea of what your baseline metabolism is doing.

If your goal is to lose weight (you can have other goals as well), you want your body to be burning fat in the morning before you eat anything.

Well, turns out what you ate yesterday is going to play a big role in what your body is doing this morning.

For example: if you had a carb heavy day yesterday, odds are your body will be burning more carbs (instead of fat) this morning. This will depend a lot on your activity level too, but the more carbs you eat, the less fat your body is likely to burn.

Ok, this makes sense. After all, low carb diets have been a hot topic for a long time now. But the Lumen doesn’t just tell you to eat less carbs (or if you ate too many carbs yesterday).

No, the Lumen app actually takes your reading and develops a personalized diet plan for your day based on your metabolic level (and your goal).

And this diet plan is based on the macronutrients- carbs, fat, and protein.

Based on your info that you put in when you sign up, the Lumen app tells you specifically how many grams of each macronutrient you should eat each day to reach your goal.

If you’re trying to lose weight (which is the goal I chose), the Lumen is going to adjust your diet to help you do that, based on what your metabolic level is.

Yesterday my brothers came over and we ate a lot of Chinese food, drank a lot of beers, and watched a few horror movies- all in all, it was a fun evening.

But I could almost sense the disappointment in my Lumen when I measured a 5 this morning (indicating I was burning almost entirely carbs).

This makes sense based on what I ate and drank last night.

Well, in order to get me burning more fat, Lumen suggested that I have a low carb day- meaning I limit my carb servings to 5 and get all of my other calories from fat and protein.

The app specifically told me how many grams of each macro I should ingest (75g carbs, 186g fat, 154g protein) based on my size and activity level.

By the way, the Lumen app is great. It has some awesome informational guides on healthy sources of all the macros as well as what a serving size of each looks like (with real examples of food).

They also give you great meal ideas using low carb and mixed carb diets.

Which reminds me, I had no idea how small a carb serving is supposed to be (and 75 g of carbs for a whole day isn’t much- the first day I started looking at carbs in foods I realized the 2 small blueberry muffins I had with breakfast where all the carbs I was allowed for the entire day).

Needless to say, I don’t do well with low-carb diets.

The app also asks you to put in what type of workouts you do and how often you do them. It also tracks your sleep schedule in order to see how long you’re fasting overnight.

The app also tracks your metabolic levels over time, which is important in determining your “metabolic flexibility” or how skilled your body is in switching between metabolic states (with more flexible being a good thing).

We want our bodies to be able to switch between burning carbs and fat efficiently, so we can eat a balanced diet and maintain a healthy weight.

Ok, to summarize- you breath in the Lumen each morning to get an idea of what type of fuel (carbs or fat) your body is burning in real time- based on this, Lumen provides you with a diet plan for the day, including exact amounts of each macronutrient you should try to consume. Your metabolic level is given on a 1-5 scale and is determined by the amount of CO2 your body is producing.

But Is The Lumen Accurate?

Discussing how the Lumen works is a fairly straightforward conversation- I might’ve rambled on a bit there, but I hope you get the gist of it.

Determining how accurate this thing is though, is a bit tougher.

And this is because I have no other way of measuring my metabolic rate to compare it against.

Now Lumen reports that they’ve done “validation studies”, and you can see the results of them here.

Basically, they show that the Lumen was determined to be accurate when compared to the “gold standard” respiratory exchange rate measured through a traditional metabolic cart.

What I can tell you is that the readings I get make sense based on my diet. When I eat a lot of carbs the day before, the Lumen rates me a 5 the next morning.

When I eat fewer carbs, I rate lower the next morning (so far my best score is a 3, but I’m hoping for a 1-2 tomorrow because I’ve strictly watched my carb intake today).

I forgot to mention it above, but the Lumen also recommends that you analyze your breath before and after workouts to see how your metabolism adjusts.

I’ve done this a few times after running and I’ve seen a drastic change in my level. I ran 3 miles this morning and I dropped from a 5 to a 1- talk about motivation.

Seeing that my body was burning fat for fuel after my workout, I decided to skip breakfast and make the most of it. I had a fairly healthy lunch (turkey sandwich on wheat, small serving of Pringles, a banana, and a Diet Coke) and a very low carb dinner.

Again, I look forward to seeing what my level is tomorrow morning, but I expect it to be in the 1-2 range.

I read another user’s review of the Lumen and they complained that their readings didn’t seem to have any correlation with their diet. Apparently they would get the same level regardless of whether they ate or fasted.

Personally, I haven’t had this issue. My metabolic levels change fairly significantly based on my diet and whether or not I exercise.

And their diet plans change based on what your level is- when I measured a 3, my daily diet plan included more carbs.

I even tried lying some on the daily questions regarding how many carb servings I ate the day before- you know, doing my due diligence for this review- to see if it affected the metabolic reading Lumen was giving me.

I haven’t seen that it has.

I’ve tried reporting that I’ve eaten fewer carbs than I actually did as well as more, and the readings still make sense with what I actually ate.

So, even though I can’t say much to how accurate the Lumen device is with determing your actual metabolic state, I can say that this device appears to give consistent readings based on my diet (and what I’d expect based on what I ate).

Final Thoughts

My first impression when I got my Lumen in the mail was that this thing sure is sharp looking. We all know that looks can be deceiving, but in this case, they aren’t.

The Lumen Metabolism Tracker comes in a sleek package that reminds me of an Apple product and the device itself is cool looking and comfortable to use.

The app is very intuitive and quite user friendly. The Lumen syncs up automatically with your phone (Android and Apple compatible) through bluetooth, making it simple to set up and get rolling right out of the box.

It comes with a nice charging stand and the Lumen can hold a charge that’ll last several days. Mine only really uses about 5% of its battery every time I use it- so far I’ve gone all week on a single charge and I’ve still got about 50% battery left.

All things considered, I’m pleasantly surprised with the Lumen.

I really wasn’t expecting much from it and I surely wasn’t expecting to enjoy using it. I planned on trying it a couple of times just so I could write this review and then probably giving it away.

But I have to say I’m impressed.

I enjoy getting a daily calculation of what my metabolism is doing and I really like the personalized diet plans for each day based on this info.

Getting real time info on how much carbs your body is burning can really help with diet planning (and I plan on using this data to help me drop a few pounds before the holidays).

Personally, I tend to have a hard time with low-carb diets and I don’t usually last very long on them. With the Lumen, I don’t have to arbitrarily abide by a low carb diet day in and day out- I can adjust my carb intake daily based on my level.

And seeing that my body is burning more fat after a workout (on an empty stomach, fyi) motivates me to workout more often.

Overall, I think the Lumen is a clever device that a lot of people are going to find helpful. I think it’s priced fairly for what you get and the 30 day money back guarantee is a great safety net just in case you don’t care for it.

In other words, I think this device is definitely worth investing in (and it would make a great gift for loved ones looking to get in better shape). Recommended.





Will's a licensed physical therapist (DPT) with over 15 years of experience treating patients from all backgrounds. He's been lifting weights and exercising in one form or another since middle school and has been working out in his own home gym for over a decade. When it comes to fitness equipment, there isn't much he hasn't tried. In his spare time, if he isn't writing or working out, he's likely playing basketball, watching movies, or hanging with his family.

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