the lumen is a device for measuring

whether or not you’re currently burning

fat or carbohydrates it’s a pretty

simple concept consisting of a co2 and

air flow sensor

and having breathed through it you’re

assigned a score of one to five one

meaning you’re mostly burning fat

five being you’re mostly burning carbs

and that depends on the co2 output of

your breath

but that’s underselling the whole system

because together with an app it forms a

complete dieting and metabolic

gamification system

if you’re the sort of person who loves

to keep track of all your health data if

you have an apple watch to constantly

take blood oxygen levels or you’re the

sort of person who does the occasional

ecg for funsies then you will love the

lumen and if you’re attempting to do a

kato diet and don’t have a reliable way

of telling you you’re currently in a

state of ketosis you’ll also love the

lumen but at nearly 300 is this a device

you or i could make use of in any

meaningful way let’s find out

i’m james bruce and you’re watching reviews so to be clear i’m

not a health nut in any way i did

actually just buy an apple watch

literally just to test this with however

i did previously use a me band five and

my motivation with the lumen is

evaluating this as a useful dieting tool

for a lay person someone like me

who probably doesn’t exercise all that


but also doesn’t eat particularly


however i will say that the app that

accompanies the lumen

has three different tracks that you can

go on that you choose when you set it up

so if you’re not interested in dieting


you can follow the track that improves

your metabolic flexibility for instance

that’s the ability to switch between

carbs and fat burning as needed

obviously if you are

strongly into your whole cato diet thing

then this is going to be a tremendous

help for you but for me

it’s just a motivational aid i think a

tool to help me understand how my diet

affects me and i guess i went into this

review without any actual expectations

it’s quite a new product category for me

i mean there is no competition for this

on the market either i have done a low

carb diet before and it worked i managed

to lose sort of 15 kilograms but as with

most fad diets i lapsed back into old

ways pretty quickly so i know that low

carb diets can work for me i just need

something to help me along the path


to motivate me and to help me understand

my metabolism so just bear that in mind

during this review

okay so onto the hardware

in the box you’ll find the lumen itself

which is basically a small breathalyzer

kind of looks like an e-cigarette and it

features a magnetic cap

a silicon coated body and a small mesh

underneath allowing you to breathe all

the way through it

there’s a charging base which the lumen

can sit on as needed there’s a usb c

charging cable that plugs into the case

and there’s also a neat little fabric

carrying case so you can keep it with

you all the time and not get it dirty

now you’re encouraged to keep it

charging overnight but don’t worry if

you’re heading away for a bit i used it

pretty extensively like five ten

measurements a day for two weeks and in

that time it only went down to ten

percent battery life so

really not a concern there

don’t worry if you can’t charge it for a

week or so it won’t matter but when you

do need to charge it just place it on

the dock and these little pogo pins will

connect and charge

it’s a gorgeously simple bit of hardware


the lumen is incredibly easy to use

there’s only one button on the device

to turn it on and it automatically

sleeps again when you’re finished

however it does need the accompanying

app there’s no way to take measurements

throughout the day and save them to the

device to sync up later

now thankfully you don’t need to faff

around with bluetooth that much you just

press it once to turn it on and then

open up the app and it’ll all

automatically pair it’s super quick and

very simple to use

inhale deeply through your lumen

hold your breath

the only slight annoyance for me was

that the app itself

takes about five seconds to load

exhale in three two


now as well as having to use the app it

also requires an active internet

connection to work as i found out when i

killed the wi-fi and data now this

probably won’t matter to most people but

it is a curious requirement

combined with the fact that