Is the Lumen Metabolic Breath Device Worth Buying?

February 20, 2020 5 min read 1 Comment

When I saw a crowdfunding campaign for a device that promised to measure your metabolism in order to send you dietary advice and help lose weight (or, preferably, alter body composition), I “supported” it without looking into the claims or science too much. The cost wasn’t prohibitive for me, and I was OK with losing the money, and interested to see what was delivered. After 18 months, I finally received the device and was able to put it to the test.

When scouring Google for reviews, I mostly fluff pieces that didn’t really dig in to the machine, stress test it, or try to ascertain its accuracy. Likely, these are PR-driven articles intended to give positive coverage. I’ve seen commercials with doctors I know who are supporting it, but the language used is quite vague, as are the promises.

First off, what does the science say about breath analysis for measuring metabolism? The Lumen, and several other marketed devices, use something called the respiratory quotient, which is a calculation based on inhaled and then exhaled CO
2 and O2. This technology can be reasonably accurate, with some literature reviews opining it as the future.i Reviews of medical machines designed for this purpose have shown to be reasonably accurate, with caveats that each machine needs to be reviewed to ensure flow rates and accuracy,ii and I have found publications from as far back as 2004, which found handheld devices as accurate as a mass spectrometer.iii The clinical relevance may be up for debate, with at least one multi-center clinical trial finding that the respiratory quotient should not be used to adjust nutrition support, due to the impact of other variables on the measurements.iv

So, the question then is, is the Lumen accurate? And is it relevant to helping individuals achieve their goals? In regards to accuracy, I could not find any publications on their exact device on their website or in searches. They do state, on their website:

In multiple studies, Lumen’s patent-pending technology was deemed to accurately measure metabolic fuel usage when compared to the gold standard RQ for measuring metabolism.”

… but they do not link to said studies. Are they published? Were they peer-reviewed? In the only somewhat negative media review I could find, New Atlas quipped


There is a hint of "too good to be true" to the technological development at its core, translating a metabolic measurement that classically needs up to an hour of analysis and large machines, into a tiny hand held device that only needs a single breath. However, the makers of Lumen call it breakthrough technology, and if it works as claimed then it surely is, although it's difficult to not be a little skeptical about the fundamental claims.”

Now for my reviews and stress tests. I found that the Lumen app had some serious limitations:


1) The app is not set up to allow extended fasting. It doesn’t allow you to “start your overnight fast” before 6 pm, and doesn’t allow you to “end” your fast after 12 pm.


2) I’ve had the fully charged device shut off between measurement breaths. After this happened, it deleted my activity and sleep from the day before

3) The app assumes close compliance. For example, if it suggests you eat 12 servings of carbs, it doesn’t let you enter 0, and caps out on the total as well. This leads to potentially frequent inaccurate reporting.

4) Has you enter your weekly work out plan in advance… as if your workout routine is identical every week. That said, it does allow you to delete and add workouts each day.

Now, here are my results, and the confusing failures of reliable data when I purposefully entered incorrect information into the app. For the first week, I used the app exactly as their protocol suggests, breathing in the morning as well as before and 30 minutes after each workout. This supposedly measures your fat burning or carbohydrate burning on a scale of 1 to 5, and my measurements were consistently “3,” with daily advice to reduce my carbohydrate intake. This is ignoring the fact that I know I operate incredibly poorly on a no/very low carbohydrate diet, but it is seemingly their only suggestion.

My first eyebrow raise happened about 5 days in, after my 48 hour fast. I fast weekly, and as mentioned above, there is no option to enter that you are on a prolonged fast, nor has the app allowed me to reduce my carbs to “0” (it lets me reduce to 2 servings most days). I work out more than normal on my fast days, to amplify the benefits, but had not worked out that day before my “fasted breath,” as that could throw off results. I again measured a “3,” as I had every day prior, and the app suggested I continue to eat the same low carb meal plan (urine strips had me at around 1 mmol/L into ketosis).

After these results, I decided to stress test the unit to make sure that faulty entered data wasn’t distorting their reported levels. First, I loaded on carbs and reduced my exercise for a couple of days. One day, my only food consumption was pizza and wine, in excess. I also stated I had exercised three times each day, and had only consumed two servings of carbs. Both days I measured at the same “3” I had following their protocol.

From there, I ate and exercised as normal for a few days to “wash out,” and then tried a stress test in the other direction. I fasted for 48 hours, while working out hard, then ate low carb low calorie for 2 days, then fasted for 72 hrs. In my second fast, my OURA ring had me at over 2,000 active calories burnt on day 1 (on top of my resting metabolic rate) and over 1,500 active calories on day 2. My urine ketosis strips had me well over 4 mmol/L at the end of the second fast. As for the app? I entered the maximum amount of carbs they allowed each day, and did not enter all of my work outs. My daily reading was a “4” out of 5 every day. Apparently, during a 7-day stint in which 5 days were fasted and the other 2 were calorie controlled and low carb, I was burning mostly carbs and advised to “lower my carbs,” but while eating pizza and drinking wine and not exercising, I was burning a “mix of carbs and fat.” It is quite clear that they have some sort of equation which takes both the breath and the self-reported data into question, and then spits out a number and recommendation, driving people to a low carb diet. Very far away from what is promised.

Some may be enjoying this, but for me, I think it is all but worthless. If you want to follow a low carb diet and need a daily planner to do it, I recommend printing off some sheets of paper for a nominal fee and tracking it yourself, while looking at your own pre-written notes of encouragement. The device and app seem no more beneficial than that strategy.


1 Response

Steven Vasquez
Steven Vasquez

February 21, 2020

I got the Lumen from Indiegogo as well. I’m not impressed so far either for the same reasons you pointed out, but hoping the software improves. There are a couple of other breath analyzers like Food Marble and Keyto, I did not order them but curious about them as well.

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