What's the deal with Lumen?
Is it a fraud? And do you need it to be healthy?
ceej on Warpcast
i have a @keccers.eth question what do you think of these https://www.lumen.me/
Challenge accepted. As I dove into the details on this one, it turned into something much longer than a cast, which is why you find yourself here. I am sympathetic to anyone who doesn't want to read all that. I've created a handy TLDR graphic for you below if you don't care about the details. If you do — read on.
What is Lumen?
Lumen is a small, vape-like device you breathe into daily, usually at the start of your day.
Using the amount of carbon dioxide in your breath, a Lumen can report to you via an app whether you are using fat or carbohydrates (glucose) as your body’s energy source. For an additional subscription fee, you can get dietary recommendations, a personalized nutrition plan, coaching, and integration with your wearables.
Over time, as the Lumen “gets to know you”, the app is able to create for you a metabolic flexibility score — a proprietary measurement that assesses your ability to adapt to changes in metabolic demand. Put more simply, metabolic flexibility is your body’s ability to switch between different energy sources depending on what you have eaten and what you’re doing that day.
While metabolic flexibility is a scientifically studied concept — the idea was created to explain how insulin resistance occurs in individuals — Lumen’s Flex score is not a scientific measurement. It’s a score they made up to assess this.
Lumen is part of a much bigger health trend around “metabolic health”. You know the drill already: society is fat, sick, and a majority of Americans have some sort of metabolic dysfunction: “88% of Americans display some level of metabolic dysfunction; up to 37% suffer from full-blown “metabolic syndrome.”.
And as it were, the best way we have to solve our problems is to throw technology and money at them, so here we are — with metabolic health vape pens and multiple different wrappers around continuous glucose monitors (think like Nutrisense and Levels).
It’s also beneficial to be thin in a sociocultural sense, and sometimes it’s hard to disentangle how much of this is truly about “health” and how much of it is about “hey this is a cool new way to diet, without counting calories”. Being skinny for skinny’s sake is seductive, and that also drives the appeal of these products, even if they do not overtly market that way.
Is Lumen a fraud?
No, it’s not a fraudulent product. It does what it says it’s going to do, mostly — but there are some limits to the device.
The gold standard corollary for the measurement Lumen claims to provide is called a Respiratory Exchange Rate (RER) measurement. You might have seen fitness people on Instagram do this — they get on a bike with a mask on and pedal really hard. Generally when people do this they aren’t seeking their RER measurement directly — RER is a component of the equation used to calculate your basal metabolic rate, or the amount of energy you use at rest.
Lumen has commissioned scientists to compare their device to what you receive when you take an RER test. I’ll let this paragraph from Mashable’s review of the device tell you how that went:
“Lumen’s internal studies and a study conducted by San Francisco State University have found that Lumen’s measurements are “comparable” to an RER measurement taken by a traditional device. However, the experts Mashable consulted — two members of U.C. Davis’ Health Sports Medicine program — aren't entirely convinced of its accuracy, or usefulness. The SFSU study concludes that "Lumen can be seen to be an effective instrument for monitoring relative, individual changes in metabolic responses (within-subject consistency), rather than a substitute for laboratory-grade RER measurements." In other words, the Lumen scale is a relative score that can track change over time, but is not an analog for a measurement you'd take in a lab.
Yet another study commissioned by Lumen came to a similar conclusion:
“A portable, home-use metabolic device (Lumen) detected significantly increased expired %CO2 in response to a high-carbohydrate test meal, and may be useful in tracking mean weekly changes to acute dietary carbohydrate modifications, especially when protein intake is standardized. Lumen measures following a high-carbohydrate diet may be better assessed under fasting conditions, whereas measures post-breakfast may be better suited for monitoring low-carbohydrate diets. Further research comparing applied versus laboratory settings is warranted to establish clinical and practical efficacy of the Lumen device, particularly in relation to end-user goals.”
In short: Lumen is useful for seeing your response to your diet for yourself over time.
Other criticisms of Lumen include:
Lumen in their marketing claims to be equivalent to RER. It is not, by their own research.
It’s unclear if it’s correct to be planning your diet around your metabolic state, rather than the activity you are going to be doing that day. Lumen may tell you that you should have a “low carb day” — but is that the best advice for you if you’re going on a multi-hour intense hike in the afternoon? You might just be setting yourself up for a bonk.
A resting RER like Lumen parallels is not sensitive to day-to-day changes, but Lumen asks you to check your measurement daily. At best, like its own study notes, it’s best to consider weekly changes, or use it before and after a certain intervention.
Why is Lumen everywhere? Why is every influencer trying to sell me this all of a sudden?
Affiliate marketing, loosely. It is now standard practice for health tech companies to offer “affiliate” (read: influencers) a cut of sales in exchange for promoting a company’s products. Lumen has one, and so if you’re a health/wellness influencer you can shill them and get money on every sale.
Depending on the company they may closely restrict who they allow to join the program, or they may let anyone with over 10,000 followers who isn’t fat to sign up. Sometimes a company will force an affiliate to use certain talking points and make them read and view educational materials about what they are selling. Sometimes the company will just be like, here’s some product links, have at it.
There’s an incredible variance in your experience as an affiliate — save for the consistently generous commissions which seem to be the one standard. For more on the mechanics of these programs — one of the best explainers of affiliate marketing in health is Bryan Johnson’s video on AG1.
Do I need Lumen to lose weight or be healthy?
The Lumen device, while not essential to a healthy lifestyle, belongs to a growing category of metabolic monitoring tools alongside continuous glucose monitors and ketone tests. These devices share a common purpose: helping people adopt lower-carb diets. However, it does not require expensive technology to do this, and many people have and will continue to successfully make dietary changes without any fancy tech tools.
Purchasing a device like Lumen can serve as a powerful psychological anchor, helping people identify as "the type of person who prioritizes health," which enhances motivation and commitment. Unlike some health metrics where awareness can trigger nocebo effects (such as sleep data potentially worsening your day if you're told you slept poorly), metabolic information about carb or fat burning states appears to have no harmful effects.
For individuals with specific needs—serious athletes optimizing performance or people managing pre-diabetes, for instance—the metabolic information provided by Lumen might offer genuinely actionable insights about how particular foods or exercise routines affect their unique physiology, provided its limitations are taken into consideration. In these cases, the device transitions from being merely motivational to potentially clinically valuable.
Would I buy the Lumen myself?
Probably not. But I’ve:
had bouts on and off using continuous glucose monitors
feel like I have a good grasp on my eating habits
Don’t feel like I can splurge on a $200 health device right now.
