One of the latest gadgets to hit the personal health and wellness scene is Lumen’s metabolic tracker, a smart device that claims to help you “hack your metabolism,” boost your energy, and burn fat instead of carbs so you can lose weight.
And all you need to do is inhale and exhale into it, and Lumen tells you if your body is currently burning fats, carbohydrates, or a combination of both. Sounds pretty good, right?
But would this device work for a vegan like me?
Let’s find out.
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Does Lumen work with vegans? 
The short answer is yes. Lumen helped me better understand my body and gain more control over my metabolism. But there are some trade-offs for people like me who follow a plant-based diet.
Whenever I hear a product say it focuses on burning fat instead of carbs, it usually means you need to eat a diet rich in meat and other animal foods like dairy, eggs, etc.
But as a long-time vegan (7 years) and vegetarian (since I was 10 years old), there is no way that I would switch to eating meat and other animal products to hack my metabolism or anything else!
Eating a plant-based diet means I eat all kinds of carbs, and in particular, I eat a lot of foods that are high in both carbs and protein, like beans.
After talking with the folks at Lumen, they assured me that vegans have success using Lumen. Although most, like me, need to tweak our diets to include more high protein and lower carbohydrates plant-based foods.
If you’d like to give Lumen a try, they are currently offering 30 bucks off any subscription with the code MHA30–this discount works on any membership length.
Yes, Lumen works for vegans but there are some drawbacks
For this review, I used the Lumen for 8-weeks, and I can say that it does work for vegans, if and only if you are willing to adjust your diet to eat more protein and fewer carbohydrates AND are ready to put in the time and effort to use Lumen throughout your day.
Using the Lumen as instructed meant I needed to severely reduce eating my favorite plant protein sources of lentils, black beans, and chickpeas and switch to eating more tofu, tempeh, soy milk, seitan, and foods made from vital wheat gluten.
Not a deal-breaker, but I admit I really did miss my beans!
How does Lumen’s metabolism tracker work? 
Lumen’s idea is simple: your breath reveals if your body is burning fats, carbs, or fats & carbs at any given point in time. So why not measure that breath at various times throughout the day?
The Lumen is a small handheld gadget that can easily go with you from home to the office and anywhere else. It looks like a large vape and comes with its own pouch and charger that you can toss into a purse, backpack, messenger bag, or even a large pocket.
So it’s very portable, which is really, really important since you take a lot of breath measurements throughout the day (more on that later.)
You use the Lumen device in tandem with the easy-to-use Lumen app 
The Lumen app (available on iOS and Android) guides you when breathing into the device, and then you see all your personalized insights and other information in the app.
The app uses AI and Machine Learning to analyze the data collected from your breath, activity, and food logs. And then Lumen processes that data to give you personalized and detailed recommendations on optimizing your meals and snacks, fitness, sleep, fasting schedule, and other wellness options. 
All that information helps you learn how to train your metabolism to switch back and forth between using fat and carbohydrate easily.
To help you record your activity, you can also connect Lumen to Apple Health, Google Fit, or Garmin Connect, and there’s even a Lumen Apple Watch app.
Lumen is not a medical device and is not FDA approved
Lumen is currently not approved or cleared as a de Novo medical device by the FDA. Lumen intends its product to be used as a tool to help people with personalized nutritional guidance.
There are some clinical studies in progress, including one on using the Lumen Device for Prediabetes Prevention and validation studies like A Handheld Metabolic Device (Lumen) to Measure Fuel Utilization in Healthy Young Adults: Device Validation Study that looks at how Lumen performs.
The Lumen measures your breath
Lumen’s science is based on the respiratory exchange ratio test (RER), which looks at the ratio between carbon dioxide production and the uptake of oxygen in a single breath.
- Low CO2 concentrations = burning fat.
- High CO2 means = burning carbs.
To use the Lumen, you perform what Lumen calls their breath maneuver: breathe one long fixed volume single breath (inhale, hold the breath for 10 seconds, and then exhale) into the device.
The device’s CO2 and flow sensor then measures your breath’s carbon dioxide (CO2) concentration on a scale of 1 to 5, which indicates what your body is using to produce energy, either carbs or fats or somewhere in between. 
The breathing part can be tricky since it needs to be a full inhale and exhale that’s not too fast or slow. I usually need to take two breaths to get a reading and sometimes, even more. 
Breathing correctly into Lumen can be frustrating!
This is especially true when you first start using the Lumen device. I had a lot of failed attempts when I started–breath was too fast, too slow, not stable or steady, and so forth.
I have asthma, so taking a big and steady inhale was hard–really hard.
Eventually, I started coughing a couple of times before measuring to clear my lungs, which helped. I ran this by a Lumen expert to make sure it’s kosher, and it’s okay!
Another tip that helps is making sure you exhale via your nose for a few seconds before taking a breath measurement with the Lumen.
Take a lot of measurements with your Lumen
The Lumen is not a device that you take one breath measurement in the morning and then another one at the end of your day.
To really use it as designed, you need to use it every day and take a lot of measurements, including before and after eating, exercising, fasting (in particular, your overnight fast,) and before sleeping. Getting the most out of Lumen requires your commitment! 
The more breath measurements you do (especially in the beginning), the better Lumen personalizes the data and the more insightful it is!
All these measurements determine how well your body switches back and forth between burning fat and carbohydrates. Something Lumen calls your metabolic flexibility.
Lumen’s goal is to help you grow your metabolic flexibility via the device and app’s insights on how well your body uses the foods you eat.
This flexible metabolism supports healthy weight loss or weight maintenance, gaining better metabolic health, and improving fitness performance.
To learn more about the science behind Lumen, check out their validation study and scholarly articles on the science that Lumen uses regarding metabolic flexibility.
What is metabolic flexibility, and why is it important? 
Metabolic flexibility means that your body’s metabolism easily switches from using food you just ate to using fat and sugars stored in your body.
So when you are metabolically flexible, after you eat a meal or snack, your body metabolizes that food and uses it immediately for energy.
And when you’re fasting or haven’t eaten in a few hours, your metabolism quickly switches to burning your body’s stored fats and sugars for energy.
Unfortunately, many of us are not metabolically flexible, and our bodies don’t easily switch from using food to burning fat and sugar stores. This is called metabolic inflexibility.
The good news is that you can train your body’s metabolism to be more flexible, so it uses fat and carbohydrates based on their availability.
And Lumen helps you get there by showing you exactly how your body responds to foods, exercise, sleep, and fasting.
Why should I care about improving my metabolic flexibility
There are a lot of benefits for people with greater metabolic flexibility, including things like better sleep, higher lean body mass, easier weight maintenance or weight loss, and sustaining energy.
These benefits are similar to those people report when fasting intermittently or following a keto diet and monitoring via a ketometer.
How Lumen helps you improve your metabolic flexibility
Lumen helps you learn the steps that result in gaining greater metabolic flexibility with its personalized insights, meal recommendations, nutrition plans, and its flexibility score.
One of the biggest benefits of using Lumen is that you start to understand how what you eat, how much the amount and type of exercise, and how much your sleep and overnight fast impact your body.
Are you currently burning carbohydrates or fats?
First, by taking breath measurements throughout the day, you see how the foods you eat, the workouts you do, the sleep you get, and the length of your daily fast impact when your body uses fat, carbs, or both fats and carbs for energy. 
Each time you take a breath using Lumen, you get a Lumen Level score between 1 and 5:
- A score of 1 shows that your body is using fat for energy and 5 means your body is using carbs.
- A score of 2, 3, or 4 means your body is using both fats and carbs.
Like I said earlier, you take a lot of measurements throughout the day.
Lumen recommends you take a reading when:
- When you wake up.
- Workouts: before and at least 30 minutes after you exercise.
- Meals and snacks: before and at least 1-2 hours after eating.
- Before you go to sleep.
- After you finish your fast (but before you eat anything for the day.)
Following these guidelines, I regularly take 10-12 measurements each day.
And yes, it can feel overwhelming. However, over time you can take fewer and fewer measurements. And that’s exactly what I did (more on that later.)
What types of foods should you eat?
Each day, following your first-morning breath, Lumen calculates a personalized nutritional plan that shows you how many grams of carbs, fat, and protein (your macros) you can eat that day.
Your nutrition plan is based on your activity level, sleep duration, length of your overnight fast, and other previous day’s information.
The nutrition plan recommendations are tailored to meet the overall long-term goal you stated when setting up the app to lose weight, improve performance, or gain better metabolic health. 
As a vegan, these macros were often challenging, especially regarding the high number of protein grams required (almost always above 100 grams for the day.)
If you need some suggestions on meals that align with those macros, Lumen offers meal plans with recipes for breakfast, lunch, dinner, and even snacks.
These recipes follow any dietary restrictions you set up in the app. So for me, the suggestions are always vegan, which is nice, although there are often only a few options, especially on Lumen’s low carb days.
For vegans like me, what would be really helpful is for Lumen to add a lot more recipes and recommendations for high protein and low carb vegan choices–because these tend to be the hardest to find on your own.
Keep track of all the macros from your meals and snacks inside the app
Lumen now offers a food tracker inside the app! So it’s a lot easier to keep track of your daily macros and stay within Lumen’s recommendations. 
Lumen’s food log includes a barcode scanner (similar to MyFitnessPal), or you can search for food by name, brand, and so forth. And if you can’t find that food, there’s an option to add it. 
I really like Lumen’s food tracker. Adding each meal’s food into the log was easy, and then the app calculates how much fat, carbs, and protein you’ve eaten thus far and how much of each remains for the day. That information helps determine what need to eat for the rest of the day. 
Unfortunately, if you already log your food in apps like MyFitnessPal or Lose It, Lumen does not currently sync with those apps, so you will need to log your food into Lumen if you want to keep track of your macros inside Lumen’s app.
Knowing and improving your Lumen FlexScore
After using the Lumen consistently for two weeks, you get a personalized Lumen FlexScore somewhere between 0 and 21 which shows you how flexible your metabolism is.
The higher the number, the more flexible your metabolism is.
- 0-6 means your metabolism is not yet flexible.
- 7 and 14 mean your metabolism is healthy.
- 15-21 means your metabolism is very efficient.
Each week you use Lumen and (hopefully) follow your personalized nutrition plans, Lumen recalculates your score based on your progress (or lack of it.)
Lumen’s goal is to help you increase that FlexScore (metabolic flexibility) over time as your body becomes better at quickly switching between burning fat and carbs throughout the day and night.
It’s easy to get hung up on this score. My advice is to not focus on any particular score but rather look at how your metabolism FlexScore is trending. Improvement takes time. 
I started at a pretty average score of about 10, and over eight weeks, following Lumen’s guidance and nutrition plans, I am now at about a 14. So trending in the right direction!
How the Lumen metabolism tracker worked for me as a vegan
In using the Lumen for over eight weeks thus far, I have definitely gained a lot of insight into how my body and metabolism work. I now better understand how food and exercise help get me into a fat-burning state.
And there were a few surprises along the way!
One of those surprises was knowing how long I should fast.
I’ve done intermittent fasting for a few years now, and by taking so many breath measurements, Lumen helped me figure out that I need a 16 hour fast each day (yikes!) to optimize my metabolism.
Another (sort of) surprise was that I was eating a lot less protein than I should
Following Lumen’s nutrition plans also showed me that I wasn’t eating enough protein each day and that I really needed to focus on eating more.
Eating more protein also helped my body get into that fat-burning zone. I also felt better and had more energy.
Getting enough recommended protein is a challenge for vegans! 
As a vegan, it is a struggle to get the total number of protein grams that Lumen recommends (more than 100 grams/day and often a lot more) while keeping carbs within Lumen’s recommendation (usually a very low carb allowance, especially for a vegan.)
On those low carb days (which is most days, at least for me), I couldn’t eat my usual protein sources of beans or lentils due to their high carb counts and had to consciously switch to eating more soy and other lower carb plant proteins. And that was tough, especially in the beginning.
It’s important to note that many carbs do not count towards your daily carb allotment, including most carbs from vegetables, especially raw veggies.
For these veggies, Lumen rates these foods as a zero carb food, and you’ll see a banner that says, “eat as much as you like!”
For Lumen, the starchy vegetables count like potatoes, corn, cassava, and sweet potatoes. Everything else, like my favorite broccoli, doesn’t count as net carbs in Lumen.
No protein powders for me. I want to eat real food!
One thing I didn’t want to do was rely on protein powders. I wanted to eat real food like I always have! So I did a couple of things:
- I added some proteins that I previously didn’t eat, especially vital wheat gluten (seitan), which is high in protein and relatively low in carbs. For anyone with a wheat or gluten allergy or avoiding wheat, getting the right balance of protein, carbs, and fats could be a challenge.
- After struggling with the low carb allowance, I reached out to a nutritionist at Lumen via the app’s chatbot, and they ended up raising my carb allowance, so I could eat more real foods that were a mix of carbs protein, and fats. This made a big difference!
- The Lumen nutritionist also said it was okay to eat less than the recommended grams of protein as long as the total grams per day were at least 75-80% of the recommendation.
If you’re a vegan trying to figure out how to meet the suggested high protein, try these out:
- Nutritional yeast (add to salads, soups, stews, or almost anything.)
- Spirulina powder to add to smoothies and other foods.
- Tofu, Edamame, and Tempeh if you eat soy.
- Vital wheat protein (seitan) if you eat wheat.
- Textured vegetable protein (TVP) or Nutrela soy chunks–gluten-free (but is soy-based.)
- Plant-based meats if okay with processed foods. There are soy-free options, like Beyond Meats, which uses pea protein, or Quorn vegan options made from mycoprotein (a soil fungus similar to mushrooms.)
- Seeds! Hemp, flax, chia, pumpkin, poppy, and sunflower seeds.
- Higher protein nuts and nut butters like almonds, peanuts, cashews, pistachios, soy nuts, or hazelnuts. Just be aware that all nuts also include high levels of fat.
- Lupini beans.
- Pumfu (Pumpkin Seed Tofu.)
- High protein plant-based yogurts and protein powders like pea protein.
- Chickpeas, lentils, black beans, kidney beans, green peas, mung bean, amaranth, and quinoa if your daily carb allotment allows (mine often did not.)
There’s also an unofficial Facebook group for vegans using Lumen, which is full of great tips and offers support and encouragement from other vegan Lumen users.
Take a lot of measurements, especially at the beginning 
For the first few weeks, I also took a lot of additional measurements outside of Lumen’s recommendations.
Since everybody is different, taking extra measurements helps you figure out how your own body responds to exercise, food, fasting, and sleep.
- For example, while Lumen recommends measuring between 1-2 hours after eating, by taking multiple measurements after eating in 15-minute intervals, I figured out that I should take a measurement about 1 hour 45 minutes after eating to see a change from that meal.
- And I learned that I needed to take a measurement about 45 minutes after exercising to see a shift in my metabolism instead of the recommended 30 minutes.
The only way to know the timing for your body is by taking extra measurements. But once you know, you don’t need to take all the additional measurements!
After about a month or so, I slowly trimmed down the number of measurements, and now I really only take a few per day rather than the 10+ that I did in the beginning.
The Lumen nutritionist said that the after measurements are the most important, so I focus on those. 
After 8 weeks, I am now taking about 5 to 6 measurements daily: first thing in the morning, after eating or exercising, and sometimes before sleep. That’s it! And it still works great.
Train your breath
I had a lot of trouble getting a decent breath measurement at the start. The app constantly told me to try again in a few seconds for various reasons, from not enough of an inhale to exhaling too fast (or too slow.)
It was beyond frustrating! 
What finally helped me was coughing a few times before taking a measurement. I needed to do this due to the constant congestion I have from asthma. I did run by this change with Lumen’s experts, and they said it was fine.
After a few days, the good news is that you’ll figure out how best to take your breath measurement. However, if you continue having problems, reach out to the Lumen Support Team or review best practices in Lumen’s video tutorials.
If you adjust your approach to taking a breath measurement outside of what Lumen already suggests, be sure to contact Lumen to run it by them to ensure it’s not impacting your readings.
Add your workouts and measure your breath before and after!
I discovered that it’s really important to add in your workouts, even if you integrate the Lumen app to Apple Health, Google Fit, or Garmin Connect.
When you connect with Garmin, Google Fit, or Apple, it should automatically add your data from those apps, including activity, sleep, steps, and floors climbed.
I did connect with Apple Health but found that the numbers Lumen showed were often inaccurate, and I needed to adjust them manually.
Adding in your workouts and breathing before/after also adjusts your nutrition plan’s carbs and fats daily allowance. The number of carbs and fats changes depending on your breath measurements and activity each day.
Also, to develop metabolic greater flexibility, make sure you exercise at a medium or even low intensity every day, in addition to any high-intensity workouts.
Low and medium-intensity training helps your body use more fat for energy versus high-intensity workouts that use carbs for energy.
If discouraged or you have questions or concerns, chat or email with Lumen
I found Lumen’s support team very helpful, especially in the beginning when I was trying to figure out how to meet the nutrition plans.
A couple of weeks into using Lumen, I almost gave up because I couldn’t get the right balance of macros and was not getting into the fat burn zones in the mornings (i.e. breathing a 1 or 2 on the Lumen.) It was so discouraging.
After getting another ultra-low-carb and super high protein nutrition plan for the day, I decided to contact Lumen and ask for a nutritionist’s help as a last attempt to keep using Lumen.
With a bit of back and forth, the nutritionist changed my carb setting to the least restrictive option that still follows Lumen’s approach. And this made all the difference for me!
To reach support, you can email them or tap the question mark icon at the top of the app and choose Support chat. It’s not immediate, but someone usually responds in a few minutes.
One tip is to ask specifically for a nutritionist to answer your questions; otherwise, you may get links to articles on Lumen’s website and more generic nutrition advice.
Join a Lumen onboarding meeting to answer all your questions
I also joined an onboarding zoom meeting about a week after using Lumen, where I met one-on-one with Noa Shani, one of Lumen’s onboarding experts.
After using the Lumen for a week before our meeting, I had a lot of questions about how to use it, when to take readings, and how to optimize using it as a vegan. So it was great to ask an expert!
I highly recommend joining one of these Lumen customer onboarding calls if offered. But wait at least a week, or more so you get a chance to try it out and then use the onboarding as an opportunity to get the answers to your questions and things you can’t figure out.
Visit Lumen’s Help Center
Additionally, Lumen’s Help Center offers a variety of answers to frequently asked questions, including many short videos to help you get started or learn to use some of the tools.
Join Lumen’s community groups
Lumen has an official Lumen community group on Facebook that’s a good resource for asking questions, finding answers, and getting some moral support. Remember that this group is for all Lumen users, not just vegans,
There’s also a much smaller niche unofficial vegan group which I highly recommend you join if you are a vegan or frequently eat a plant-based diet.
Lumen’s cost
Lumen is now following a subscription model, offering anywhere between a 6-month commitment to a 12 and an 18-month membership. The device comes with a membership, so you don’t pay anything extra. 
Currently, Lumen offers a 30-day free trial where you can return the Lumen for a full refund within that 30-day window. After which, you are charged $249 for 6-months, $299 for 12 months, or $349 for 18 months.
Lumen currently offers a discount on any membership length using promo code MHA30 to receive a $30 discount off your subscription purchase.
Is Lumen worth the cost?
Yes, at least for the short term while you develop greater metabolic flexibility.
In my experience, once you learn how to train your metabolism to be flexible, you can apply those lessons without a subscription. You won’t, of course, be able to measure your breath to confirm or use the Lumen app’s features.
I’ve learned so much in my 8-week trial and changed my eating, sleeping, and exercise behaviors that I have cut back my readings to a few per day.
And I still see my metabolic flexibility improving. So for me, a 6-month membership is likely enough.
However, if you thrive on knowing where you stand and want to measure your breath and get Lumen’s feedback, then purchasing a longer subscription is a good choice.
Final thoughts on Lumen
After first hitting a few bumps in the road getting Lumen to work for me, I’ve enjoyed my time using Lumen. I think of Lumen as one smart tool in my wellness practice that includes my Apple Watch (or Fitbit.)
I find Lumen helps me be more accountable: in what I eat, how much I exercise, and how long I maintain my daily fast.
Following Lumen’s nutrition plans and logging my food directly into the app helped improve my metabolic flexibility score by 4 points! I’ve also lost a few pounds, even though that wasn’t my main goal.
And most importantly, I feel better. I have more energy throughout the day. And for me, feeling better overall is what matters most, no matter what the scale shows.
So if you want to lose some extra weight and gain more control over your metabolism to be metabolically flexible, Lumen is a great tool to own and use–as long as you use it regularly and repeatedly throughout your day. And I think it makes sense to track your macros using Lumen’s app.
But using Lumen does require commitment and practice. So if you are someone who doesn’t like the idea of taking measurements throughout the day, Lumen may not be for you.
And if you are looking for a short-term solution, Lumen is also likely not for you. Improving your ‘metabolic flexibility is a long-term process that leads to weight loss or performance improvement over time. It’s not a quick fix.
