Lumen Review: The Science behind Metabolism Tracking + my experience



Medically reviewed by Dr. Steve Kim, MD


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Metabolism plays a significant role in weight loss. However, for many people, our metabolism seems like something that is beyond our control. There is a common belief that it’s just something we are “born with” and cannot be changed.

So for people with a poor metabolism, that sucks.

BUT that theory isn’t necessarily true. You can learn more about your metabolism and use these insights to improve the way your body processes food and burns fat.

Lumen is changing how we think about this aspect of dieting and nutrition. It’s a small breathalyzer that syncs with a smartphone or Apple Watch app to tell you if you are burning fats or carbohydrates. Using its technology, we’re able to learn far more about how our metabolism responds to what (and when) we eat. 

Let’s explore what Lumen is and how you can use it to help your metabolism.

Table of Contents

Lumen with phone, wallet, and keys
Size comparison of my Lumen vs my iPhone 11, Ridge wallet, etc.

What is the Lumen?

At first glance, the Lumen looks like an inhaler or e-cigarette vape. However, unlike those devices, when you exhale through the Lumen, it tells you what kind of energy your body is currently burning: fat or carbohydrates.

By understanding which type of energy your cells are burning, you can understand:

  1. How efficient your body is at burning calories
  2. When you should eat
  3. What you should eat

How does Lumen work?

Lumen describes their device as a metabolic tracker. But what really is your metabolism, and how does the Lumen help out?

Metabolism is a critical physiologic process. Our body’s metabolic rate measures how much energy we expend in a particular time. Typically, it’s calculated daily. Metabolism describes a broad set of chemical processes that occur in the body. Per the Mayo Clinic, processes are things like:

  • breathing
  • digesting food
  • cell breakdown
  • cell creation

Each of these processes requires energy, which comes from food. As a result, metabolism is linked with nutrition because it’s powered by food — mostly fat or carbohydrates.

Generally, the body burns carbs (in the form of glucose) because it’s easier and quicker. However, once stored carbs have been used, the body can switch to a new fuel source: fats. The process of switching between both sources is referred to as metabolic flexibility. This metabolic flexibility, btw, is really the key to all-things-Lumen.

Metabolic flexibility is the ability to respond or adapt to conditional changes in metabolic demand. This broad concept has been propagated to explain insulin resistance and mechanisms governing fuel selection between glucose and fatty acids, highlighting the metabolic inflexibility of obesity and type 2 diabetes.

Cell Metab . 2017 May 2;25(5):1027-1036. doi: 10.1016/j.cmet.2017.04.015.

According to Lumen, metabolic flexibility has several positive effects, including:

  • Better health
  • Stronger immune system
  • Easier weight loss
  • Consistent blood sugar level
  • Better sleep 
  • Optimized workout performance

Overall, people with diabetes and obesity tend to suffer from metabolic inflexibility. Exercise has a considerable influence on this process, and there’s also evidence to suggest that diet plays a role too.

But, how does the Lumen metabolic tracker work? It simply measures the CO2 level in your breath. The device can state whether you are burning glucose or fat by taking these levels.

The Lumen measures the respiratory exchange ratio (RER). This compares the ratio of CO2 you exhale vs. the O2 you inhale.

  • RER of 1 = carbs are being burned
  • RER of 0.8 = protein is being burned
  • RER of 0.7 = fats are being burned

But how legit is that all this science? Let’s check below.

Is the science behind Lumen legit?

So what is the science behind the Lumen

As mentioned above, its aim is “measuring metabolic fuel utilization” via a handheld device. The most accurate way we know to measure metabolic rate is with a metabolic cart. These machines are considered the gold standard of measuring:

  1. the carbon dioxide produced
  2. oxygen consumed from breathing.

When these two measures are combined, we can assess metabolic fuel usage, i.e., (carbohydrates vs. fats).

However, metabolic cart machines are expensive, difficult to operate, large, and only available in a clinical setting.

patient on a bike with a metabolic cart machine
This could be you. But hopefully not.

The Lumen was developed to measure metabolic fuel CO2 via a handheld device. A study by San Francisco State University tested the Validity of the Lumen® handheld metabolic device to measure fuel utilization in healthy young adults.

The results of the study were crazy positive. It showed the validity of the Lumen “to estimate metabolic fuel utilization in a comparable manner with the “gold-standard” metabolic cart.” The research concluded that the Lumen provides convenient real-time metabolic information for users.

That paper isn’t the only research that has been performed on this device.

Overall, the technology seems legit. It’s based on existing accepted clinical measures that are used in widespread professional environments. However, as with all novel technologies, it will benefit from further research.

What’s it like using Lumen?

Now that you understand the science behind the Lumen, it’s time to discover what it’s like to use it.

Firstly, the device itself is stylishly designed and made from superior materials. The build quality is solid, and overall it has a premium look and feel. The device and charging pod are mostly metal, with a matte black finish. It’s definitely built to last.

To start using the Lumen, you need to charge it and download the app (iOS, Android). To operate the Lumen, you’ll need your smartphone or tablet. The device won’t work on its own; it needs to be connected by Bluetooth to log in and perform measurements. 

Some may find these a little restrictive and would prefer a standalone device. However, it’s pretty convenient because the Lumen connects excellently with the app.

Once you download the app, you will be asked a series of questions to tailor the Lumen towards your needs, such as:

  • Personal details
  • Activity level
  • Reason for using Lumen
  • What functions do you require?
Lumen in my gym bag
The Lumen is small enough to be super portable

The user onboarding process is very smooth and intuitive. It takes about 5 minutes, it’s user-friendly and straightforward for users of every level.

Once you’ve filled out the details, you link the Lumen with your smartphone via Bluetooth.

The Lumen is ready to do the first measurement. To start, you click on the “air” button at the bottom of the Lumen and begin.

The process is simple:

  1. Sit down in a relaxed position and with a resting heart rate.
  2. Place the Lumen in your mouth, and inhale when the app directs you. This practice takes a little getting used to, so just breathe in small amounts of air slowly if you are having difficulty.
  3. When the ring goes green, remove the device and hold your breath for 10 seconds, as instructed by the app.
  4. Then, exhale into the device at whatever speed the app tells you to. There’s also a graphical interface that helps you find the right level.
  5. Once you’re done, the app will tell you what metabolic state your body is in.

If all that is unclear or sounds confusing, Lumen’s onboarding also features several videos that make the process simple. 

When you exhale into your Lumen, the results on your phone will be displayed on a 1-5 scale.

lumen metabolism scale 1-5
Lumen results scale
  1. You are burning 84-100% fat for energy.
  2. Using mostly fats, from 63 to 80%.
  3. You are using both fats and carbs, 42-60% fats.
  4. Carbs are mostly being used; 60-77% carbs.
  5. You are running on carbs for energy, 80-100%.

Which levels you are on will depend on your aims. If you are trying to stay in ketosis (i.e., on a keto diet), you’ll want to keep between 1 & 2, i.e., burning fats for energy. 

However, if your aim is to achieve metabolic flexibility, bouncing between all five levels is what you’ll want.

Once the Lumen gives you your rating, it offers you a daily meal plan based on the goals you’ve inputted previously. Essentially, these suggestions come down to high, medium, or low carb diets.

The app offers suggestions for meals for breakfast, lunch, and dinner. Each meal is customizable and provides ingredient swaps that maintain the protein, carb, and fat ratio.

But that’s not where the customization ends. You can input allergies or dietary preferences like vegetarian, vegan, pescatarian, and so on.

Who is Lumen a good fit for?

People who want to better understand their metabolic health

Lumen gives you super accurate readings of what fuel your body is burning and can make nutritional recommendations to improve your metabolic flexibility. This gives you insights that you normally wouldn’t have.

With Lumen, meal planning also becomes easy to maintain. Instead of just telling you what to eat, Lumen helps users understand how their bodies react to certain food types.

People trying to lose (or gain!) weight

The Lumen is a great device for people trying to lose weight. It comes with several nutritional plans that offer a good amount of flexibility while helping to achieve your goals. The app has similarities to some calorie counting apps that track your fat/carb/protein ratio. However, it relies less on self reporting, and more on making dynamic dietary recommendations.

Anyone in the biohacking space

The accuracy and reliability of its readings will appeal to anyone trying to get the most from their body.

People on a keto diet

Currently, many keto dieters use ketone strips to measure if they are burning fats. While the Lumen won’t directly measure ketosis, it will accurately indicate if you are burning fats.

At the end of the day, you probably have a good sense for whether or not you’d benefit from having a Lumen in your life. If you’re someone who’s genuinely interested in the technology, and you’re confident that you’d use it regularly (because you need to!) then it very well may be a value-add for you.

When should you take your measurements?

Lumen recommends that users take their measurements multiple times during the day.

☀️ Morning: Morning is the best time of day to take a measurement. After your body has come out of a fasting state (i.e. during sleep), Lumen can recommend a suitable daily meal plan.

💪 Pre & Post Workout: Lumen’s measurements can help guide you about which foods you need for certain types of exercise, and also indicate how your exercise has impacted your body.

🍆 After Meals: Measuring your metabolism 1-2 hours after meals gives insights into how your body reacts to certain foods.

💧 After Fasting: Testing in the morning or after your intermittent fasting hours can give you an idea of your metabolism’s state.

⏰ Random Checks: Lumen also recommends a random check during the day to help you build an idea of how your metabolism is functioning throughout the day.

Is Lumen worth it?

Depending on your goals, Lumen can be worth it. It’s also worth noting, though, that the Lumen is the type of tool that you’ll really need to use consistently to maximize its value. And at a $250 price tag, this is that much more important to remember.

Lumen offers three different pricing tiers:

  • Metabolism Booster – 6 months = $249
  • Advanced Fat Burn – 12 months = $300
  • Optimal Health – 18 month = $349

This includes the device and a subscription to the app, insights, tracking, and dietary recommendations. Once the 6, 12, or 18-month subscription is up, Lumen charges $19 per month for access to the app. 

You can also score an extra $30 off by using the code ZMW30. Lumen offers a 30-day money-back guarantee. 

Lumen also has stellar customer support and boasts a solid App Store rating of 4.5 stars.

Advantages of Lumen

  • Excellent build quality with premium materials
  • Extremely accurate at reading metabolism
  • Easy-to-use app with very helpful onboarding videos
  • Impressive variety of recipes and nutrition guidelines
  • Integration with a variety of fitness devices, like Apple Health
  • The Lumen app works seamlessly with the Lumen itself

Disadvantages of Lumen

  • It only works with a smartphone. So if you’re someone who’d rather use a desktop app, you’re SOL
  • At around $300, the Lumen is arguably pretty expensive
  • While the device is portable and includes a nice carrying pouch, you’ll need to carry it around with you everyday. So if you’re someone who’s always forgetting their keys… start remembering.

Lumen Reviews: What are other users saying about their experiences?

Don’t take my word for it, I’m just one guy. We also read through a bunch of customer reviews across Reddit, Trustpilot, and Instagram to get a feel for what the Lumen community is saying, as a whole. 

Take a look at some of the standouts that do a good job of painting the overall picture.

The Verdict: Is Lumen legitimately useful for improving your metabolism?

Lumen is an excellent device for anyone who is struggling to lose weight. It helps users understand their metabolism and gain a better understanding of the type of diet that is best suited for them. 

For biohackers and anyone who loves precision, Lumen is a great tool. 

Of course, it’s worth remembering it’s a tool; not a miracle solution. To get the most from the Lumen, you need to use it regularly. Additionally, you’ll need to follow the dietary recommendations. If you are disciplined enough with this approach, you’ll benefit from the device. Depending on your goals, it will be well worth the money.

The main draw is that the Lumen is quite expensive. It’s a slick, well-built device, but with an entry point of $259, plus a $19 subscription after six months, using the device for a year will set you back the best part of $380 (before discounts, that is). 

While that total is a lot, it’s a significant savings when compared to a personal nutritionist —  which is what Lumen is in many ways. And of course, it’s also a valuable tool that provides insights into your metabolism that will last forever.