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Lumen Metabolism Tracker In-Depth Review

It almost sounds like something out of a sci-fi movie. Every morning for the last twenty days, I’ve started my day by grabbing what could be mistaken for a vape pen off my nightstand and breathing into it deeply. I breathe in slowly, hold my breath, and then breathe out and within a few seconds, I see a number on my phone screen indicating whether I’m currently burning fat or burning carbs as my primary energy source. 

Even though I grew up as a child during the 1990s, when technological advancement started to move at a blistering pace, it still baffles me to think that there’s a device small enough to fit in your pocket that can non-invasively assess your metabolism. The implications for being able to do so are pretty significant, too, especially if you’re interested in biohacking or fine-tuning your diet to meet your fitness goals. 

Of course, any time something sounds too good to be true or seems exceptionally promising, it’s healthy to approach it with a dose of skepticism. After all, there are plenty of brands in the fitness industry that make millions off of what is essentially just the placebo effect and some flashy branding. 

In addition to trying out Lumen for myself, I wanted to do a little digging and investigate their claims, technology, and outcomes to get the full picture. In this article, I’ll cover my experience using Lumen and the Lumen App, and then I’ll unpack the broader context around the device. 

If you decide to try Lumen for yourself, feel free to use this link and code BLAKE30 for $30 off your purchase. However, please read this article first to make sure Lumen is right for your fitness needs! I share links like this to help make a little spare cash from the work I put in here, but I always want readers to confirm that what they're getting is what they need. 

My Experience Using Lumen

Lifestyle - Lumen and Phone 3

As mentioned above, I’ve been using Lumen for almost three weeks. I measure my metabolic rate in the morning upon waking and then again in the evening before I go to sleep. Less consistently, I also use it to take midday measurements or pre-workout measurements. 

How to Use Lumen to Measure Your Metabolism

The process of using the Lumen is pretty straightforward. You open the app, select the type of measurement you want to take (pre-workout, morning, evening, pre-meal, etc), and then you power on your Lumen device. 

Once the device is warmed up, you follow onscreen prompts to breathe in slowly, hold your breath, and then exhale slowly. The app will process that for a moment and then you’ll be instructed to do it again. Each measurement requires two breaths. 

Once you’ve completed both breathing cycles through the Lumen device, it gives you your score for the day. Scores are in a range from 1 to 5, with 1 meaning that you’re burning almost exclusively body fat and 5 meaning you’re burning almost exclusively carbs. 

Lumen’s Food and Diet Suggestions

Depending upon your goals (which you specify in-app during setup), Lumen will then make a recommendation for your food intake for the day. It shifts between recommending low carb days, high carb days, and blended food intake days. 

Within the app, you can also put together a meal plan that meets the recommended macros. The recipe functionality inside the Lumen app is pretty slick and easy to follow. I’ve only tried a few of their recommended recipes since I prep meals in advance at the start of the week, but I was happy with the ones that I tried. I’m handy in the kitchen, but it was nice to see that I could still grab a snack recipe that wouldn’t require too much prep time. Plenty of the recipes are pretty flavorful, too, which is good since my half-Mexican palate needs some spice and flavor.  

Lumen Has an Interesting Relationship with Carbs

Going into trying out Lumen, I was mainly skeptical because I had previously seen a few keto influencers discussing it alongside their discussions about the evils of carbs. 

As a personal trainer (and again… a half-Mexican who is rarely going to turn down chilaquiles or frijoles), I do not agree with the keto mentality. Carbs are not evil. Carbs, like all food, have no moral alignment. They’re not good, they’re not bad. They’re just food. All food, regardless of its macros and composition, is just fuel and it doesn’t have to (and shouldn’t) be assigned moral value. 

Because I had seen keto bros discussing Lumen as a way of confirming that they had successfully avoided carbs, I feared that the app would approach nutrition from the same mentality. Thankfully, it doesn’t. 

Often carbs become a scapegoat for dieting because plenty of high carb foods are also high-calorie foods. When you reduce your intake of high-calorie foods to the point where you’re sustaining a caloric deficit over time, you’re going to lose weight– it’s not necessarily because of the carb reduction but because a calorie deficit is a calorie deficit. Yet, the low carb mentality has become engrained in US culture as a quick (but not sustainable) way to lose weight quickly. So, often when I hear about a brand that focuses on burning carbs, there are usually red flags for me. I assume that they’re going to take the same “carbs are bad” approach that a lot of other brands have. 

Within the Lumen app, though, I don’t get that impression. To be fair, I did set up my personal health inventory to indicate that my primary fitness goals are around building strength and muscle, not losing weight. It’s possible that there’d be more of an emphasis on low carb days if I had chosen weight loss as my goal, but based upon my experience with the app, it seems to recommend a healthy blend of low carb days, high carb days, and days that are somewhere in between. 

Lumen Focuses on Metabolic Flexibility

On the Lumen app and website, one of the facets of their approach that they spend quite a bit of time discussing is metabolic flexibility. 

Metabolic flexibility is “the ability of the human body to switch back and forth between fat and carbohydrates based on their availability.”

Part of the Lumen philosophy is that your body should naturally fluctuate between states of fat burning and carbohydrate burning based upon your activity level and food intake. They approach it through the lens of fueling your body in the way it needs to be fueled rather than restricting yourself to a specific subset of foods and macros. 

Often this type of flexibility can be difficult for folks to stick with, but the in-app prompts and advice definitely make it easier for beginners. Even if it is more challenging to stick with, it’s also a healthier approach than cutting out entire groups of foods altogether. 

Fact or Cap: Is Lumen Actually Backed Up By Science?

While my experiences with the app and device have been positive, I always think it’s important to zoom out and consider the broader context, especially when it comes to fitness and wellness technology. 

Blake's current results on Lumen

According to Lumen, it has been a great week of waking up in a state of fat burning for me after a week of primarily burning carbs.

How Does Lumen Work?

According to Lumen’s own documentation, “Lumen uses a Co2 sensor and flow meter to determine the carbon dioxide concentration in a single breath that indicates the type of fuel your body uses to produce energy. The measurement of the CO2 concentration is achieved by using a unique breath maneuver. This breath maneuver is performed by inhaling a personalized volume of air, holding it for 10 seconds, and exhaling. The CO2 concentration values and range, which are measured and calculated by Lumen, are unique and personal to each individual.”

While that may sound complicated or far-fetched, what this essentially means is that research has shown that your respiration is affected by your metabolism. Your respiratory exchange ratio– the ratio between the metabolic production of carbon dioxide (CO2) and the uptake of oxygen (O2)– tells us a lot about what is happening within your body from an energy production standpoint. States of fat burning and carb burning have been shown to produce different concentrations of CO2 in your breath, and so Lumen looks at this CO2 concentration as an indicator of what is happening metabolically. 

This isn’t dissimilar to an approach used by technology developed for the US Military in a device called COBRA- the Carbon dioxide/Oxygen Breath and Respiration Analyzer. Additionally, lab tests conducted at San Francisco State University (not yet peer-reviewed at the time of publishing this article) concluded that Lumen was able to gauge respiratory exchange rate comparably to “gold-standard” lab equipment. It’s important to note that the article I’ve linked to this research is not yet peer-reviewed. The current research and presentation of the data do seem promising and scientifically sound, but I’m willing to say that my assessment may change depending upon broader scientific community consensus. 

Whether or not Lumen compares to the benchmarks set by medical lab equipment, what does seem confirmed is that Lumen does a decent job of assessing fluctuations in your respiratory exchange ratio. Even if later research questions the precision of its measurements, it could still be a useful tool for noticing trends and tracking trailing indicators, which can still be really helpful. 

Pending further lab studies, though, it seems safe to assume that Lumen does what it claims to do– provide real-time insights into what’s going on with your metabolism. 

A Secondary, Non-Marketed Outcome

One of the byproducts of a lot of fitness technology is something that often isn’t discussed or marketed by the brands that produce these products: awareness. 

The use of a fitness tracker, metabolic rate analyzer, or other forms of wellness technology often necessitates that you consciously think about your food intake and your activity levels. US culture is one that encourages activity on auto-pilot. We seldom think about why we’re doing what we’re doing, and just go with what we always do. 

Having a device like Lumen prompting you to slow down, take a measurement, and then consider the impact of the food that you’re eating is simple yet countercultural. It goes against the autopilot mentality. 

If we ignore the respiratory exchange ratio measurements and just consider the fact that it forces users to bring awareness to what they’re eating and how active they are throughout the day, it’s already valuable. The hardest part of training and nutrition is being aware of how much you’re eating. That’s why food journals are often recommended to folks who are just trying out a bulking or cutting diet. Lumen achieves that element of forcing you to think about what you’re eating, which can then give you the acuity to make decisions you may not have made otherwise. 

Final Thoughts: Is Lumen Worth It? 

Lumen comes with a 30-day free trial. After that, it will cost around $300 per year, which comes out to about $25 per month. 

All-in-all, that’s pretty affordable, especially since a lab test to measure your respiratory exchange ratio would require sitting in a waiting room and paying upwards of $300-500 per individual test. 

Additionally, I have found that the Lumen app contains a lot of useful information and resources that go beyond the individual Lumen score. The recipes, for example, can really help with meal prep and measuring your macros. I already pay for a separate app that does the same thing, so if I bundled the two together and just paid for one app, that’d help. 

Finally, the device itself is sleek and easy to use. The battery life is great, it’s not difficult to take your measurements, and you can easily track the impact that your diet is having on your metabolic rate in real-time. 

It’s fair to be skeptical of any piece of fitness technology, and I definitely want to read more quantitative research on Lumen’s efficacy as it comes out. As it is, though, the evidence seems to be in favor of Lumen doing what it says it's going to do, and the apps, community, and resources available to subscribers do help users make mindful decisions about their health. 

So, overall, I would say yes, Lumen is worth it.

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