Lumen Metabolism Tracker review

  • Price Paid:$250.00
  • User rating:
  • Would buy again from this company: Yes
  • Used product for: 4 months
  • # of logged workouts:

"There are so many nice touches to the product, it's hard to remember what a technological miracle it is to measure whether I'm fat burning or carb burning at any moment in the day. It's sleek, it's small, it turns itself off, the voice in the app that coaches you how long to breathe in and then breathe out has a wonderful user interface that isn't annoying even after months of hearing, "Breathe deeply through your Lumen..."

The main idea is to be in fat-burn mode more often and for a longer time (if you are trying to burn fat, which most of us are). The device shows you how you are doing, then recommends food to eat that day to keep you on track toward greater metabolic flexibility. There are explainer text blurbs, videos and more, and you can even order food so you can choose exactly what you need each day to match the recommended carbs, fats and proteins.

Having worked with a nutritionist the first half of this year, and started using Lumen in late spring, I stuck with my nutritionist's menu until July, and then when I started giving myself more flexibility, I was comforted by being able to check in with the Lumen, and to get advice on macros. My workout schedule also syncs with Lumen (in a limited way) and so Lumen recommends more carbs on long cardio days. It has a nice graphical way of representing the values of various foods as carbs, proteins and fats, and many veggies don't count toward the total carbs, which I agree with. There are little notes, like, we know avocado has fat in it but you should eat it because of XYZ. I did notice it recommends me to eat a lot more fat that I had in the past, and it's hard to find sources of fat that don't also have a lot of carbs, so that's been a learning curve for me. Nuts, cheese and avocados perform well for that.

I measure each morning when I wake up, and the app cheers me on when I wake up in fat burn. It keeps score of how many mornings per week you wake up in fat burn, and gives advice on how to improve, such as not eating too close to bedtime, and sleeping seven to eight hours.

Overall, this is an AMAZING piece of technology, and the app is just as great as the science, which is rare. I never feel confused using it. My complaints are really around the categorization of food and having the app consider the time of day and whether I consumed workout fuel during the workout. I think this should be accounted for differently so I could compare a long run with water only to a long run with energy gels or sports drink. It is possible to measure my breath when I return from the run, but it's not as accurate if I've eaten any of that fuel within the last hour and if my heart rate is still elevated from the activity. That's more a limitation of how our bodies work than the devices fault, but maybe they could run a formula against those particular measurements to compensate somehow. Anyway, overall it's very very cool to do such advanced measurements without even getting all the way out of bed. This device was provided to BT for reviewing purposes. I will be renewing the app subscription personally. Here is our affiliate link to purchase Lumen.


Very well designed to be easy to use with the companion app.


Very well made and designed, both from a scientific perspective and the physical device, charger, and packaging. The battery lasts WEEKS before needing to be recharged, depending how often you test your metabolism.


Sleek, high-tech, compact, and beautiful.


The device takes a few days/weeks to "learn" you and then will give you a Flex score daily. The science and engineering seems quite sound, which influences the limitations, which I describe in the Weaknesses section.

Compared to the other options for measuring whether you are in fat burn or carb burn, Lumen is the clear winner. Although it uses RQ measurement (Respiratory Quotient), which is often accomplished with a blood test and an hour in a metabolic chamber and a team of professionals, this company has figured out they can measure the carbon output of a single breath using a handheld ... breathalyzer, essentially. So I could spend hundreds of dollars for a single measurement, or I could buy a bunch of wasteful keto strips that can be thrown off by dehydration, OR I could breath into this chic little black thing a few times a day. Well, I know which one I choose. Entering food in the log is easy. Most foods are already there, and entering a new one isn't too bad.

Even though this product was developed by twin sister PhD scientists who are endurance athletes (triathletes, specifically) the device and it's software and instructions weirdly make it harder for athletes. My biggest issues were that you are supposed to wait 30 minutes (without eating) after a workout to take a measurement. This really cuts into the prime time for eating immediately after a workout. There's also no way to figure out if fuel you consume during a workout is helping. Additionally, the way you log your food to compare you eating to what you are burning doesn't work that well for athletes. You can log food as breakfast, lunch, dinner and snacks. This doesn't account for the time of day, pre-workout or post-workout meals, or those athletes who eat five or six small meals per day. I don't consider the Infinit I drink on the bike to be a "snack" but there is nowhere else to categorize it.

Buyers clubMetabolism Tracker
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  • workouts logged
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