| Manufacturer | Lumen |
|---|---|
| Type | Handheld metabolism tracker (breath CO2 sensor) |
| Price | $299 at full price; often on sale between $99 and $199 |
| Subscription | Required, about $19 a month, for the app guidance and tracking |
Specifications and features as at launch.
Expert opinion | Specifications | Battery life | Features | Further reading
Expert opinion
My partner and I have used Lumen for over three years. It is the only consumer device I know of that estimates whether you are burning fat or carbohydrate from your breath, using a CO2 sensor and a score from one to five. In my four comparisons against a blood ketone meter, Lumen agreed with the blood reading in three. That is reasonable for a non-invasive test, but not conclusive.
The limitations matter. Lumen is not medical grade and has no oxygen sensor. Readings need the same breathing technique every time, and two readings five minutes apart can differ by a point. It cannot be used during a workout, so wait 30 minutes afterwards. Deep ketosis can produce a false carbohydrate-burning reading. The published studies involve Lumen staff, although some are now peer reviewed. The app and its daily nutrition guidance need a subscription of about $19 a month. I lost 1 kg in the first month, which I put down to paying more attention to what and when I ate.
Lumen Metabolism
Track actual carb and fat burn.
RRP $199
10% more off current sale price - use code: FATBURN
Get it nowOrder now – Lumen Metabolism Also sold direct bySpecifications
| Device | |
|---|---|
| Sensors | CO2 sensor and flow meter |
| Dimensions | 102 x 41.4 x 33.3 mm |
| Weight | 75 g |
| Water resistance | Not waterproof |
| Operating temperature | 15 to 40 degrees C |
| Storage temperature | -30 to 70 degrees C |
| © the5krunner. Link required. | |
| Power | |
| Battery | Lithium polymer, up to 14 days in normal use |
| Dock | USB-C, 145 g, 14.5 x 79.5 x 68 mm |
| Use per charge | More than 50 breaths per charge according to the review; a third-party source says 8 to 10 breaths |
| © the5krunner. Link required. | |
Battery life
| Item | Detail |
|---|---|
| Battery | Up to 14 days |
| © the5krunner. Link required. | |
Features
- Measures breath CO2 to show whether you are burning mostly fat or carbohydrate
- Validated by Lumen against RER on a metabolic cart
- Daily guidance from the app on fuelling
Lumen Metabolism
Track actual carb and fat burn.
RRP $199
10% more off current sale price - use code: FATBURN
Get it nowOrder now – Lumen Metabolism Also sold direct byFurther reading
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- Garmin 90-degree charging adapter: Charges your Garmin from any USB-C cable. Essential when travelling. I use one.
- Body Glide: The blue anti-chafe stick swimmers and runners carry. I use it.
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- Compressport R2 v2 calf sleeves: My calf sleeves of choice. I use them.
- Cellucor C4: My pre-workout before hard sessions.
- TPU tubes: Schwalbe Aerothan, Tubolito and Pirelli SmarTube. Light, tiny spares. I use all three.
- G8 insoles: Adjustable insoles that are good. I use them.
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Watches and sensors
- Polar H10: My daily driver for waking HRV.
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- Apple Watch Ultra 4: My daily smartwatch. No phone needed on rides.
- Garmin Fenix 9 Pro: I’ve just bought one.
On the bike
- Continental GP5000 for everyday riding, and Aero 111 on the front for special occasions.
- Helmets: Specialized S-Works Evade 3 for road riding, and Rudy Project Wing for TT-style races. I use both.
- Ravemen FR300: A front light that mounts under your Garmin or Wahoo. I use one.
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Home and indoor training
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Health, recovery and sleep
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- Eight Sleep: A cooling mattress cover my partner and I use nightly.
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