Lumen Review + The Keto Diet: The ultimate guide

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Lumen Review - how does this work on Keto?
If you’ve read lumen reviews, you know they don’t always focus on keto – our review is here to change that.

Don’t miss our Lumen Keto Review – we’ll help you discover if the device is right for you.

The Lumen is a new device to help you manage your metabolism. The Lumen will tell you whether you are burning carbohydrates or fat for fuel. It’s the first device of its kind, and it can be used as an alternative to measuring ketone levels in your blood, urine, or breath. We’ll cover how the Lumen works and if it’s right for you!

If you’ve read any other of the countless Lumen Reviews out there, this one will be a little different: we’ll specifically focus on what this smart device means for someone practicing Keto to burn more fat

Lumen Keto: Not the best option for keto'ers
Lumen Metabolism Tracker
  • Designed to “hack your metabolism.”
  • Incredibly well-designed
  • Peer-tested and review
  • But it is right for keto?
Buy Now A Keto Alternative
We might earn a commission if you make a purchase, at no additional cost to you.

What is the Lumen Metabolism Tracker?

The Lumen Metabolism Tracker is a smart device + incredible mobile app that helps your metabolism

Lumen is a device that helps you measure your metabolism. It tells you if it’s burning fat or carbs. You can also use it to track your food and exercise. It syncs to an app with custom-made nutrition plans and other resources for you to use in order for you to live a healthy life.

Lumen has been proven, in multiple studies, to meet the gold standard of measuring metabolism (called Respiratory Exchange Ratio, or RER for short).

Lumen Tracker: It starts with a breath

Lumen Review - it starts with a breath

Lumen, the world’s first hand-held, portable device to accurately measure metabolism.

The Lumen device is a CO2 sensor and flow meter that measures the breath of an individual to show their metabolic rate. It can tell you what fuel your body uses for energy production, which could help those who are trying to manage stress, sleep or improve performance with food intake.

It’s like having your own personal nutritionist. Know what and when to eat so that you can fuel your workout, improve metabolic flexibility, support fat burn- all while making the most of every meal.

Why I wanted to do a Lumen Review

Keto allows for lots of steak!

I’ve been doing the Keto diet for more than 10 years. Yes, before it was even cool.

If you’re on this page, you probably know what the Keto Diet is. But if you aren’t aware, the Keto Diet is a high-fat, low carb diet that helps you burn fat instead of carbs.

The Lumen is a way to measure your metabolism and can help provide insight on whether you are in ketosis or not, so I wanted to test it out for myself.

What’s the Keto Diet?

Ketogenic diets (or the Keto Diet, for short) have been around since the 1920s as a treatment for epilepsy (the first one was developed by Dr. John Freeman). The keto diet comes from this history – but today we know it works wonders for weight loss!

When studying the Keto Diet for epilepsy they found an unintended (but pleasant) side effect: weight loss.

The weight loss was such a noticeable side-effect that the keto diet became quickly known as a great “diet.”

Try pairing Lumen with SweetKick mints to reduce sugar cravings.

TIP: Check out the Best Keto Product on Amazon. Also, try using SweetKick with Lumen. Read more in our SweetKick Review.

How Lumen Works… and the connection to Keto

Before Lumen, you had to use something like this to get your RER

Lumen says, “The science isn’t new, but the technology is.” Before the Lumen was available, one could only measure their metabolism by a costly and time-consuming test in a hospital or clinic (through the breath using Respiratory Exchange Ratio – RER).

Now, with Lumen, that has all changed. Lumen measures RER using a sensor and flow meter that measures the CO2 in your breath to provide the same measurement as lab testing.

If you are on Keto, you know that it’s important to get your body in ketosis. Ketosis is a measure if you are burning carbs.

When carbohydrates are being used for fuel, the body naturally produces more CO₂ than when using fats – and this difference in levels can be detected through a breath test (using technology like Lumen). That’s what the Lumen device measures.

Does Lumen measure ketones… or ketosis?

A ketone meter, like this one, take a blood sample to measure blood ketone levels – another metabolic tracker.

The short answer is no.

Lumen will tell you if your body is using carbs or fats as a source of energy.

The Lumen device does not measure ketones at all; instead it is an alternative measurement to ketones, measuring CO2 and this reading can determine whether your body is burning fat or carbs.

Ketone levels can tell you if your body is in ketosis. This means that your body is using fatty acids to make energy for the brain. To get into ketosis, it takes fasting or not eating (or limited) carbs for an extended period of time.

Higher Lumen levels and ketosis can occur due to diet-induced ketosis when one’s carb intake is very low and fat and protein intake is rather high.

In short, the Lumen wasn’t 100% designed for someone on Keto. Lumen doesn’t make that assertion on any of their materials. This is also a common (and heated) topic on the very active Lumen Community Facebook Page. That doesn’t mean that I’ve abandoned the Lumen Smart Tracker.

I’ll dive more into what I found as we continue this Lumen Review.

Lumen Keto: What device does measure if you are in ketosis?

The best device, besides a traditional keto meter, is the Keyto Breath Sensor (read our full Keyto Breath Sensor Review).

Must Have Keto Device
Keyto Breath Sensor

Eliminate keto confusion with just one breath. The Keyto Breath Sensor allows you to find out EXACTLY where you fall in ketosis and stop you from stalling out.

Buy Now Our Keyto Review
We might earn a commission if you make a purchase, at no additional cost to you.

What is the Keyto Breath Sensor?

The Keyto device is a sensor that detects acetone levels in your breath. Acetone is a biomarker for ketosis, which means that it can tell if you are in ketosis or not. Keyto uses this information to tell how well your body is using fat for energy. If you are in ketosis, it means that your body is using fat for energy instead of carbs. This can be helpful if you are trying to lose weight (or if you have diabetes).

In short, if the lumen was designed for keto – it would be the Keyto sensor (read more about this in our Keyto Review).

How do you actually measure if you are burning carbs or fat burn with the Lumen Device?

I know this is all pretty scientific up to this point, but the Lumen app makes it incredibly simple to do. The app is incredibly designed and makes this very scientific process very easy for anyone to do.

Lumen walks you through the steps for a measurement.

It’s really easy:

  • Simply open the app
  • Select take a measurement (the app will ask you some questions to get an accurate measurement – if you’ve eaten, before bed, after sleeping, etc)
  • Turn on your Lumen Device (the only button on the device)
  • Put your lips on the Lumen
  • Take a deep breath in, while your lips still on the device – until the circle grows to the green
  • Remove lips from the Lumen and hold your breath
  • Lumen will audibly tell you to put your lips back on the device
  • Put your lips back on the device and blow – but keep the ball in the grey area
  • Wait a couple of seconds
  • Lumen will give you a score – the lumen score.

The Lumen App will give you a “Lumen Score” on a scale of 1 – 5. 1 means you are in fat-burning mode, 5 means you are in carb-burning mode. And the number in between represents somewhere on the mostly fat-burning/mostly carb-burning spectrum.

Lumen Review: What We loved

First things, first. We loved a lot about Lumen.

The Lumen Device and Lumen App

The Lumen Device and the Lumen iPhone application are incredibly well done. They did an incredible job making a very complex product with a lot of science behind it and making it very easy to use.

The device itself is beautiful. It’s like if Steve Jobs designed a medical device. It’s seriously that beautiful.

How easy it is to use

We’ve tried a lot of smart products that are supposed to just “work” and they do not. The Lumen is incredibly easy to use and Lumen walks you through step by step.

Lumen also does a great job of allowing you to set up notifications around when you want to be “nudged” to take a measurement (in the morning or in the evening, for example).

Many apps don’t allow you to have this level of control.

The incredible amount of information Lumen has

The Lumen website is full of tons of information. Furthermore, the Lumen Community is full of people that really love – and care – about Lumen.

Lumen Accurate? It’s peer reviewed

Are you in fat-burning mode or not? This lumen review is clear: they do a great job explaining this via the lumen app.

The science behind lumen and the respiratory exchange ratio is incredibly sound and peer-reviewed.

There are also tons of studies on the importance of what is called “metabolic flexibility.” Lumen talks a ton about metabolic flexibility on their website and there are actually a ton of scientific articles about this, too.

What is Metabolic Flexibility and how to hack your metabolism?

Metabolic Flexibility is the ability of your body to change between using carbohydrates or fat for fuel based on availability. Lumen calls this “hack your metabolism.”

As mentioned, there are a ton of scientific articles about metabolic flexibility, I was most surprised to find that this concept is actually something that we can train our bodies to get better at.

Metabolic Flexibility has been around for years now but has only really gained traction over the last few decades because of its importance in regulating weight management. 

It makes sense when you think about it in terms of diabetes. How do you become diabetic? You become diabetic when your body cannot use the carbs in food as efficiently for fuel as you used to. Your cells stop responding to insulin, and so glucose builds up in the bloodstream. By definition, you become metabolically inflexible.

Research shows points to a lot of evidence that this (“hack your metabolism”) is key to a strong and healthy metabolism, in general. A strong and healthy metabolism is crucial for weight loss.

How lumen measures your metabolism flexibility – the Lumen Flex Score

The key to using Lumen and getting the most from using Lumen is using it often. You will only get your Lumen Flex Score after using it for two weeks.

The lumen app tells you where you are in the journey and creates your lumen flex score – we loved this lumen app as part of our lumen review.

Lumen also wants you to do measurements before eating a meal, after eating a meal, before a workout (or any physical activity), and after a workout to give you a much better score.

Furthermore, they want you to get a Lumen score before and after eating a high carb meal and low carb meal.

They also want to know about your intermittent fasting habits, how much you slept, and a lot more.

This helps provide a Lumen Score (mostly fat burning vs mostly carb burning) which is used to provide your Lumen Flex Score (how flexible your metabolism is).

What does Lumen do with the Lumen Level?

The biggest thing the Lumen Level does is provide you with insights on what you should be eating and helps put together a full nutrition plan. This meal plan makes it easier to get increasing your Lumen Flex Readings and helps you plan what your meals should be. It is your metabolic tracker.

The way they visually show this information in the app is incredible and very easy to understand. The app will even update your high carb days and low carb days based on what your Lumen level is doing on any given day.

The app is simply incredible. Not only does it handle your Lumen level readings, but also helps with nutrition, sleep, and intermittent fasting.

Keto and Lumen – My Experience

For this lumen review, we wanted to know: was this good for measuring ketone bodies?

Outside of cheat days, I keep my diet very low carb – around 30 net carbs per day. I’ve been doing keto for over 10 years and I’m always interested in new ways to hack my metabolism.

I heard about Lumen, the first device that helps you “hack” your body into being more metabolically flexible and burning fat instead of glucose as fuel. It sounded like a great idea because it would offer me another way to increase Metabolic Flexibility. But that’s actually not what happened: and it’s not Lumen’s fault.

It is really hard for a person that has been doing hardcore keto, like I’ve been doing for so long, to mess with the levels of carbohydrates they consume on a regular basis.

In other words: it’s really hard for me to follow the Lumen program.

Trust me, I’d love to have another high carb meal (I definitely can’t have a high carb diet) – it’s just easier for me to keep in nutritional ketosis and a VERY occasional cheat day.

If you want something like Lumen, but designed for the Keto Diet, then check out Keyto and our full Keyto Review. It’s much better suited for people on the keto diet. The device is very similar, in fact, but is focused on measuring ketosis.

Must Have Keto Device
Keyto Breath Sensor

Eliminate keto confusion with just one breath. The Keyto Breath Sensor allows you to find out EXACTLY where you fall in ketosis and stop you from stalling out.

Buy Now Keyto Review
We might earn a commission if you make a purchase, at no additional cost to you.

What Lumen recommends: adjusting carb intake to help you become more metabolically flexible. This means consuming more carbs on some days and fewer carbs on other days.

The end goal of Lumen and the ketogenic diet are the same: get your body burning more fat (AKA get your body in a fat-burning state) to lose weight.

Lumen’s program emphasis training your body to be more flexible (burning mostly carbs when it needs to and burning mostly fat a majority of the time). The keto diet gets your body used to burning fat almost all of the time.

baked bread
Both carbs and fats can help you improve your lumen score through the lumen breathalyzer.

Some research shows that Keto may lead to insulin resistance, while other evidence states that people who eat keto have more healthy blood sugar levels.

If you are on keto, check out our Keyto Review. That’s not a typo – it’s the new device that is more suited for the keto diet.

Another key sticking point: my schedule

While they look cute here, these two are a lot of work in the morning!

Let’s do some real talk, people. My schedule is nuts.

I’ve got two kids: ages 2 and 4 as of writing this, and the mornings are simply insane in the membrane. The hour after they wake up and the hour before they go to sleep is simply chaos.

As I’ve mentioned several times, this blog is a hobby that I do at night. I have a “real” job where I am typically on calls all day long, usually starting first thing in the morning.

I know Lumen’s instructions are simple, at least on the surface: take a measurement every morning after being still for 1 minute.

But sometimes that’s even a challenge for me in the morning. I typically wake up with the kids, get them going and run to jump on my first call.

Since they are typically on video, that makes it tough to even use Lumen on the video call. People would think I’m using an e-cigarette or something.

Once again, Lumen: it’s me, not you that doesn’t work in the relationship. I know I should have 1 minute to spare in the mornings, but sometimes I don’t.

An interesting correlation: stress, sleep and Lumen

I noticed an interesting correlation between my Lumen level and stress and sleep. Here’s what Lumen says.

Lumen Level and Stress Correlation

Stress may trigger your body’s fight-or-flight response, which elevates your stress hormone levels, primarily cortisol and epinephrine. These hormones affect your metabolism by shifting your body to use more carbs for fuel, which results in a higher Lumen level.

Lumen Level and Sleep Correlation

When you don’t sleep well, your sympathetic system sends signals to your brain to seek food in order to stay alert. This raises your stress hormones, mainly cortisol. Cortisol affects your metabolism by inducing your body to use more carbs for fuel, which results in a higher Lumen level.

In other words, the more stress I was feeling, the higher my Lumen level would be.

The same is true with sleep, the less I sleep (or if I had a night of poor sleep, like the kids were awake all night) the higher my Lumen level would be.

Note: you are shooting for a lower Lumen level in the morning. When you wake each morning, take a Lumen breath measurement. Ideally, it should be 1 or 2. This means that your body will burn fat while sleeping and fasting for a short period of time.

What we can all agree on

While we can spend all day arguing if have a flexible metabolism is better or worse than strictly following keto, there are a couple of things that we can all agree on, that Lumen gives us insight into:

  1. In general, we eat way too many carbs
  2. Training our body to burn fat vs. carbs is good for a variety of different reasons
  3. Sleep matters
  4. Stress level matters
  5. Intermittent fasting is important

In general, those top 5 things are more important for your overall health and fitness level than a proprietary score.

Too many people think that one tool or one diet is the answer to all of their problems (or even just how to lose weight) – but in reality, we probably make this more complicated than it needs to be.

Lumen Review: Who it’s REALLY designed for

The Lumen isn’t for me. But that’s ok. Not every product we try is going to be a perfect fit for us. However, that doesn’t mean the product isn’t designed and could be the right fit for you.

I don’t need to lose a massive amount of weight. I’m not massively overweight, but I may have a couple of pounds that I could lose. Don’t worry, I won’t post pictures of myself shirtless or anything crazy like that. 

I’ve been doing the Ketogenic Diet for so long for a very simple reason: the Keto Diet because it simply works for me.

That’s the key to any long-lasting diet/exercise/weight loss program: find something that works for you. 

To many, I think this is an excuse for, “If it needs to work for me, then it needs to include a donut every day.”

That’s not what I’m saying. Find something that takes the pounds off, keeps the pounds off, and something you can turn into more of a lifestyle.

The truth is, if you can’t make something like Lumen work for 2 weeks, it’s probably not right for me. The keto diet is right for me because I can follow it.

If you can commit to two weeks of measurements – then give Lumen a try.

Lumen even offers a 30-day money-back guarantee. I’m not a math major – but 2 weeks is shorter than 30 days to give this a shot and see if it’s right for you.

Lumen Keto: Not the best option for keto'ers
Lumen Metabolism Tracker
  • Designed to “hack your metabolism.”
  • Incredibly well-designed
  • Peer-tested and review
  • But it is right for keto?
Buy Now A Keto Alternative
We might earn a commission if you make a purchase, at no additional cost to you.

Have any questions or comments about our Lumen review? How did it compare to other Lumen Reviews? Let us know in the comments below!

If you want a better option for people on the keto diet, check out our Keyto Review. Want some great Keto Snacks? Check out our Genius Gourmet Review, our Immi Ramen Review and the best keto snacks on Amazon.

5 thoughts on “Lumen Review + The Keto Diet: The ultimate guide”

  1. This is exactly the review I was looking for! Keto works for me, and I have a feeling it will be a very strange process giving in to the science behind Lumen when I’m set in my low carb ways.


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