Can a Carb Breathalyzer Help You Lose Weight? I Tried Lumen to Find Out

What’s Good About Lumen?

Teaches you how your body uses fuel

After you take the slow, measured breaths into the Lumen, the app spits out a number, one to five, that indicates whether you’re burning more carbs or fat. If you get a 1 or a 2, you’re in the fat-burn zone, while a 4 or 5 suggests your body is mostly fueling off carbs. A 3, rather obviously, is a relatively even mix of fat- and carb-burning. Spend a few weeks—at least two, per Lumen—and you’ll receive a metabolic flexibility score on a 0 to 21 scale (higher is better, or more flexible), which indicates your body’s current metabolic flexibility.

What I found after the first month of using Lumen sounds unremarkable, but had a serious impact on how I approach eating and working out. I almost always woke up in a fat-burning state, just before I went for a morning workout. This isn’t ideal, as my personal goal was and is to improve athletic performance—there is a “performance” track goal setting in Lumen—which, generally, you want to be fueled by energy-rich carbs instead of fat.

Lumen’s solution for me was simple and effective: On big workout days, eat a carb-heavy breakfast when I wake up, and delay my training session until the afternoon. Readings taken a few hours after this carb-rich breakfast—overnight oats or whole-grain toast with a banana, typically—showed my body moving into the carb-burning territory, which was my signal to hit the gym. 

My example is performance-focused, but you can see how Lumen—either directly or indirectly—trains you how to use it effectively and understand what’s going on in your body.

Supports weight goals

I’ll cop to this up front: I wasn’t using Lumen for weight loss, which seems to be its biggest selling point. I’m relatively healthy and it wouldn’t be healthy for me to try and lose weight to review a product. That said, it’s evident that weight loss through Lumen’s metabolic management is a breath of fresh air in a market where you typically find some truly abominable products. 

Virtually every letter, word, sentence, and paragraph within the app points toward sustainable, long-lasting lifestyle shifts rather than exploitative or extreme Lose 10 Pounds A Week!-type claims. There wasn’t a single time I used Lumen when I felt the product was shaming me for not eating what it suggested, or bullying me into overly restrictive diets. Instead, it sends a steady stream of things you can add to your diet or do to inch closer to your goal—be it weight loss, athletic performance, or general metabolic health. 

After a few months of admittedly rigorous and occasionally tedious use (more on that later), you’ll undoubtedly find Lumen has subtly changed how, what, and when you eat. This process takes time; it took me a month or so before I registered daily scores in the ranges Lumen wanted me to in pursuit of my goal.

Potentially a good value

The technology is a first. Its efficacy is backed by a growing list of unaffiliated, peer-reviewed published research. This is deserving of praise, especially in a category where marketing often means tricks, grand claims, and outright fabrication—Lumen does not promise that you will lose a certain amount of weight in a certain amount of time, only that if you use it as intended it can help you along your health journey. 

That said, $299 upfront with another $19 per month is a significant amount of money. A full year of using Lumen will run you $508 before tax and second costs. But seeing as the product is unique unto itself, there’s no direct competitor to compare prices with, and you could certainly justify roughly $45 monthly for a wholly new technology that does what it says it will do, should you put in the time and effort required. 

Some new-age health tech like the continuous glucose monitors (CGMs) designed for non-diabetics paint Lumen as downright affordable. Nutrisense, for example, is one of the most visible brands in that space and costs $229 a month at the cheapest rung of the price packages—and that price is only available if you buy a full 12 months of service ($2,748 in total). That said, CGMs have to be resupplied every two weeks or so, and analyzing blood sugar levels seemingly requires more hardware than dissecting CO2 levels in your breath. 

I’d never suggest Lumen is affordable or inexpensive, but I would push against the somewhat popular notion that it is unfairly expensive. It’s not difficult to envision a world in which Lumen was made with more expensive-feeling materials and marked up to $1,000 for the device alone.

Very well-designed

The how and why of Lumen is undeniably confusing for the layperson. It took multiple discussions with a dietician, hours of poring over academic research, and a freakish devotion to understanding CO2 breath level measurement to scratch the surface of Lumen’s “metabolic flexibility” concept. Thankfully, I don’t think you really need to understand the how or the why to see results. 

The app is pushy in a good way in that it frequently reminds you to take a breath measurement at the correct intervals, which eventually becomes second nature. It also tells you in simple terms what’s on the menu for the day, whether you like it (high-carb day!) or not (low-carb day). Metabolic-focused breath analysis is heavy on the jargon, but Lumen does a fairly good job at insulating you from the sciencey acronym thicket and translating your RERs and CO2% and mitochondrial density figures into plain English. 

I grew to appreciate the build of the device itself as well. My partner came to call it a “carb-shaming vape,” which just about nails its aesthetic. It’s about the size of one of those thick Sharpie markers, doesn’t weigh much, and the material is grippy without being sticky.