You’re probably here for one of two clear reasons. Either you’re thinking about getting a Lumen, and you’re looking for unsponsored reviews, or you have no idea what I’m talking about and you want to make sense of this word in this context.
Or maybe you accidentally clicked this open…regardless, welcome! I hope that my experience here is useful to you. I hope you’re ready for a long read with a lot of images!
First – let’s start by clarifying an obvious term. “Lumen” is the name of a company and a device. I pay Lumen to use my Lumen. This device is a tiny breathalyzer that measures CO2 output to determine if you are burning fats or carbs for fuel. Lumen’s goal is to teach each user how to become metabolically flexible; specifically to train your body to burn carbs as efficiently as burning fat. The app comes with a ton of support such as recommended daily macros, recipe ideas, workout motivation, and nutritionists available in-app. A lot of people turn to Lumen to actively influence their metabolic health. Two tracks are available: weight loss, and fitness.
Second – this isn’t a sponsored post. I paid for this out of my own pocket, and am simply sharing my experience with it. My overall impression is “meh; I can take it or leave it.” I am not quite their target audience, and I find the limitations significant. But that’s just me, and I’m not you. Read on for more details about how I use my Lumen now, and how I plan to use it in the future.
Disclosure: This site contains affiliate links; I may earn a tiny commission from purchases – but not from Lumen, I am not part of their program.
So I bought…a Lumen.
A Lumen device is a tiny breathalyzer that gives real-time results about what fuel source your body is using at any time.
Q. What Sparked the Purchase
A. Curiosity of course!
Lumen is in the realm of biohacking devices, and has a lot of appeal for people like me (folks who are actively trying to improve health and longevity). You don’t have to identify as a biohacker to use one, you just need a credit card and a set of lungs.
In January 2022 my doctor requested fresh lab work, so I had my fasting blood drawn a few days before our appointment. At the appointment my doctor shared that my fasting glucose was prediabetic.
I was floored, because I don’t have any other markers for type two diabetes, but my doctor wasn’t too worried. He suggested that I start making some diet and lifestyle changes, and that we’ll check my A1C later in the year. This is when I realized that my previous weight loss stalled for two entire years; my body’s Fat Burn Mode was broken and I needed to fix it ASAP.
Did I want a Lumen to fix my “Fat Burn Mode?” Not really – I actually tackled my high glucose with daily berberine (usually just 500mg while fasting, in the morning with coffee). Berberine was the kick I needed to lower my glucose, and that resulted in immediate fat burn. I lost 10lbs and my fasting glucose dropped 20mg/dl in about five weeks…that was all the proof that I needed about glucose getting in the way of my body burning fat. [Be advised that my beloved Thorne Berberine-500 is no longer available on Amazon as of June 2022. I did find the 500mg on Thrive Market, and Amazon now carries a smaller 200mg dosage which may be better for some tums. I don’t experience indigestion with the 500s, so I’m buying mine on Thrive Market while I can.]
But I still wanted data to support my suspicions, and understanding my CO2 output sounded great.
However, paying $300 for a Lumen and subscription did not sound great. So I sought a second-hand device, and found one readily on eBay. One week and $100 later I had my own Lumen.
My initial concerns were the usual concerns after buying a used gadget.
“Is it clean?” “Does it work?” “Will I hate this?”
Luckily my second-hand Lumen device seemed as good as new – no evidence otherwise.
First Use Reactions
I was super excited to use it right away, and it was as I expected. Learning the app took a little time, but it’s user friendly overall. Lumen does require a specific breathing pattern to get a reading, but it’s easy and the app gives users as much practice as you need. All you do is inhale deeply through the Lumen, hold your breath, then exhale back into the Lumen. It’s not a steep learning curve, but I definitely pinch my nose when I take breath measurements because I don’t trust my sinuses to hold my breath. (Nose pinching isn’t required – that’s just my preference.)
I really like the optional menstrual cycle tracking. Lumen syncs that data with Apple Health, so if you track with Apple, the information carries over. I like seeing what part of my cycle I am in, and the recommendations for that specific phase. For example – when I was between days 15 and 22, Lumen noted that I could “avoid breakouts by helping your liver process any excess estrogen. Try kale, broccoli, onions, garlic, and radishes.” This sent me down a little research rabbit hole about anti-estrogenic foods, and I wasn’t too surprised that it’s basically a list of the things I love to eat.
It’s worth noting that I can use their cycle tracking because I have a normal cycle, and I am not taking any hormones for regulation. It was just a toggle that I qualified to opt in to. I wish I could toggle off the personalized nutrition plan!
Quick note about cycle tracking since Roe vs. Wade was overturned. A lot of women are deleting their cycle tracking apps to avoid potential subpoenas in the event of needing a formerly-legal healthcare procedure. If this is you – look up Stardust Period Tracker (developed by Stardust App LLC). They use end-to-end encryption, so your personal health information stays private.
Changes After First Use
The first weeks were full of many small changes, and the current conclusion is that I do not and will not use most of the functionality. Let me expand on that a bit.
Lumen calculates a daily nutrition plan for each user. The plan is shaped by the track; weight loss or fitness, and the first measurement of the day.
The macro (carbohydrate, fat, and protein) recommendations are nice, but I will not use them.
You are supposed to log your food, meet your macros each day, and follow their plan…but that’s far too fussy for me. I don’t have an analytical relationship with my food, and I don’t want to see my food as calories or macros. For the record, I also prefer to eat (and serve my family) whole foods that don’t have nutrition labels – like organic cucumbers with salt and vinegar, and grass-fed ground bison cooked with ghee and sesame oil. Exact numbers are unknown, because I don’t care. I care about a large variety of high quality real foods, and eating until feeling satisfied.
For the record I tried to meet my macros for one day. I couldn’t do it. I honestly logged my food, and had already blasted past my carbohydrate allotment, only met half of the fat recommendation, and had only met a quarter of my protein by the end of dinner.
So there I am in the pantry with Mister Jupiter, zero percent hungry, and trying to figure out how to cram in at least 50g protein. That’s when I just walked away and started ignoring the food recommendations entirely. *Just felt all of the macro counters collectively gasp.*
I know, I know. It’s wild; I am out of control.
Truth is that if I am not hungry I am not going to eat.
An app sure as hell won’t change that, so I will continue to ignore all of its recommendations and prodding for me to log my meals. I’m also not going to reach out to an in-app nutritionist because I’m not looking for help; I’m only here for the data.
I like the recipes in the app, but it doesn’t work for my lifestyle – because I am a menu planner and I plan for the family. If our menu says “lasagna” but Lumen recommends that I have a low carb day -I’m eating regular lasagna with my family- because that was the plan, and that’s how I run this ship.
- Related: How I Make Weekly Menu Planning Easy
Custom Tags to Label Breath Measurements
I like the custom tag feature for logging breath measurements outside of Lumen’s defined options, but the current (June 2022) app doesn’t allow multiple tags for a single breath measurement. Kind of silly that we can’t combine “after fasting” with “before a meal” because I know I’m not the only faster who uses Lumen (more on fasting with Lumen soon).
Speaking of custom tags, I use mine primarily because most of Lumen’s presets don’t match my lifestyle. It would be a great match if I ate four times a day and had structured exercise time…but I don’t. I might eat twice a day, and I my exercise is just walking because that’s what I can do with my toddler.
Sadly, custom tags cannot be edited. When I take a custom measurement, but my toddler taps my phone, or if I have an internet issue, it defaults to “Custom check-in” which isn’t bad, it’s just not convenient when I intended to label it something more specific that I would like to track.
How I Use it in Our Environment
Our environment is just our house. I use it when I’m home, and I have only wanted to use it away from home once. I usually leave it on the dining room table because that’s usually where I break fasts and such. I sometimes take my bedtime measurement earlier than my actual bedtime because Lumen uses midnight to define days. Lumen’s app doesn’t really accommodate shift workers or night owls right now – surely this will change because not everyone goes to bed before midnight.
How I Use it in Our Life
In my life, I’m only going to use Lumen for data once a year. It confirms some notions, and I like seeing what I blow when I think I’m in ketosis. But I don’t need everything that’s in the app, and I refuse to stress out about macros EVER AGAIN. I am very happy as an intuitive eating intermittent faster.
Speaking of fasting – let me share what I’ve learned from fasting with Lumen
Preface- I have been fasting daily for about three years. Before now I used to fast regularly in my 20s because I worked a lot and often left my wallet at home. Now I am intentionally fasting for general health and fat loss; I am a seasoned faster.
- Related: Intermittent Fasting, Month Thirty 📍
Lumen cannot tell the difference between burning ketones or burning carbs because it only measures the CO2 output and both fuel sources produce higher CO2 than burning fatty acids. Another source of high numbers is stress. The Lumen community is stuck on insisting that higher numbers when fasting indicate that the body is stressed by the fast, and that people need to eat frequently to avoid such stress. So if you are intermittent fasting, and you want community support, I do NOT recommend Lumen’s FB community for fasting support.
I know my body. If I wake up burning fat (blowing a one or two), then later blow higher while fasted -I know it’s because I’m either stressed for other reasons (like swerving around couch cushions on the interstate) -or- producing ketones; not that “fasting for 15 hours is too much” because it isn’t.
But that’s just me. I trust my body to give me the feedback that I need, and I know from experience that I can comfortably fast for about 80 hours (which isn’t common, I actually prefer eating every day). Trusting my body’s feedback is also how I’ve successfully lived so long without a scale…because I pay attention to how my clothes fit. Tight clothes = salad time. Loose clothes = enjoy the nachos.
When I log my morning measurement, Lumen prods me to input yesterday’s macros (that I refuse to follow), and gives me the opportunity to predict my fasting hours for that day. The default range is 8:30pm to 8am, a tiny sub-12 hour fast (…a “fast” that short is commonly called digestive rest because it’s not really fasting. It’s far from the fat-melting-ketosis-and-autophagy sessions that I prefer). Luckily, the fasting hours can be modified any time. This is good for me because I never know exactly when I’m going to break a fast. Yesterday it was 4:30pm, today is was 2pm. It just depends on if I actually want to eat; because I only eat when I am hungry regardless of what the clock says.
If you regularly fast longer than 24 hours, you may not want to bother logging with Lumen. The app won’t save fasts over 24 hours, and the ranges can’t be changed. Fasts can only start between 1pm and 1am, then they can only end between 6am and 6pm. For the record, I only logged my fasts for one week so I could show you what it looks like. Otherwise (surprise!) I don’t care, because I don’t get validation that way. I gain validation when my clothes fit better.
Q. But what about metabolic flexibility?
A. I can carb cycle on my own just fine. My problem in January 2022 (and Jan 2021 actually) was my pre-diabetic fasting glucose numbers. I’ve already made serious headway just by taking berberine most days. Repairing my fasting glucose feels like it’s helping me re-establish metabolic flexibility. I can’t really articulate this intuition, but it’s just another dimension of trusting my body (or rather, those clever gut microbes). Truly I prefer a mostly low-carb life, but I also make space regularly for beer and pizza; macros be damned.
- Related: Pizza & Beer Yearbook
How is Metabolic Flexibility Measured? How is it Improved?
Lumen uses your unique breath measurements to determine your flexibility, and gives it an arbitrary score of zero to 21 – it’s called a Lumen Flex Score. Low numbers indicate inflexibility, 15 and up suggest an efficient and flexible metabolism.
My first Flex Score was 15; the lowest number in the most efficient range. This wasn’t a big surprise, but I was happy to see my suspicions validated. Flex Scores are updated on Mondays, and the first one needs two weeks of data to calculate your first score.
How Lumen Guides Carb Cycling
Earlier I mentioned that “I can carb cycle on my own,” but I didn’t explain what that is. Carb cycling is a term used for mindful carbohydrate ingestion – specifically having periods of very low carb intake, and occasional high carb days. Flexible metabolisms can use both fuel sources just fine, and Lumen encourages carb cycling by giving metabolically flexible users Boost Days.
I got my first Boost Day after getting a good Flex Score. The goal of a Boost Day is to have plenty of carbs to demonstrate my metabolic flexibility. So the breath measurements before and after meals are extra important – because you want to see a good carb burn after a high carb low fat meal.
Lumen recommends foods like fruits and beans to reach your carb macros on Boost Days, but you already know that I won’t heed their recommendation. I treated myself to rice, beans, enchiladas, plenty of queso, and a margarita.
I picked up Tex-mex for Kid Jupiter and I on my Boost Day. Things were going great until he refused to eat his fried avocado, and wanted to eat my rice instead (this is why I refuse to stress out about meeting my macros). So he had my rice, and I ate his fried avocado on my low fat day. After dinner I blew a one – meaning that I was burning fat. It was either the avocado, or a byproduct of my margarita. Regardless, we had a lovely dinner, and my size eight jeggings fit great – that’s what I really care about.
My overall impression is “meh, I could take it or leave it.”
The recommendations, plans, and structure are super great for the people who want that.
But I only want basic data, so I am disappointed that I must pay for ALL OF THE THINGS when I just want the bare bones readings. If it was a “freemium” app – I would be the person who was happy with the free version and never want bonus features.
However, I am happy to have the data so quickly. I had one indirect calorimetry test years ago on Fort Leavenworth. It measures metabolic rate by analyzing gas exchange – it takes 15 minutes, and includes a weighted face cover to control air flow. Lumen is much faster; measurements take one minute at the most, no headgear required.
So the speed is nice and I like the available recipes, but I’m not a fan of the pricing, and especially not happy with the device limitations that have hindered my own use.
Pricing and Limitations
These were unfun lessons to learn.
I wish that companies were just up front about pricing – without having to hunt around the internet and send emails to support.
Lumen makes clear pricing for new users that need a Lumen device. They do NOT make pricing clear for folks like me; new users who bought a Lumen elsewhere. The breathalyzer is basically free, what we pay for is the subscription to use the damn thing. You can either pay $25 each month, or $20/month when you buy an entire year at once.
Everybody must pay Lumen to use their Lumen.
Also the app requires internet to work at all; there are zero offline functions. Let’s say that you have bad signal at home – too bad, buddy. Maybe you travel and want to use your Lumen in places without cell signal or internet (like an airplane) – you’re out of luck.
Other limitations are in the app, and less surprising.
– Only one tag per breath; when I measure before a meal I have to pick either “after fasting” or “before eating” because I can’t use both. So I often breathe my “after fasting” measurement about 10-15 minutes before I log my “before eating” breath.
– I would expect the fasting tag -provided by Lumen- to add up my fasting hours (or at least open the door to that functionality). Lumen provides an “after fasting” tag, but a “finished eating for the day” tag (or similar) would be a super easy way to log fasting hours that wouldn’t get in the way of “after eating” or “before sleeping” breath measurements.
– Custom tags cannot be edited. I mentioned this one already. It’s not the end of the world, it’s just not desirable when an accidental press selects a different tag…and I’m stuck with it.
– Limited fasting support. I detailed this one earlier too. TL;DR is that the hours are fixed, and fasts over 24 hours are not allowed.
Thoughts for Future Use
Despite my un-love for this device, I’m going to keep it for at least a year, but I only want to pay for one month each year. My use this month has simply confirmed that I am already metabolically flexible. Sure, there’s room to improve, but I don’t actually need its guidance.
My plan is to only buy a subscription for June; a little birthday gift to myself. I’m paying to use it now (June 2022), and I intend on buying another single month activation for June 2023. After that? I’ll probably sell it and try to recover $50. I like that I get quick information, and that it confirms when I am burning fat. But that’s it really; I don’t need the help that it’s offering, and I refuse to see my food as macros.
I just want to have a month’s worth of breath data for my birth month. That data will be shared in February 2024 when I share my 50th month of fasting. Maybe I’ll be a Lumen lover by then? Unlikely, but hey – maybe they will offer a stripped down version of their app. I’d pay…$50/year to measure my CO2 output anytime; and skip all of the fussy stuff that I ignore anyway.
Meanwhile – I’m going to keep using my Lumen until my one-month subscription expires. Well…I need to contact them to avoid the automatic charge (🙄). I’ll email them this weekend because subscriptions can’t be canceled in-app.
I’ll be back to share what happens after your Lumen gets bricked.
What Happens When Your Lumen Subscription Expires
Update expected in July or August 2022.