Realtime Metabolic Testing with Lumen

Real time metabolic testing - that's the objective of a new to the market product called Lumen. Here's a first look and the background to its development

Last updated -

There is no shortage of gadgets to help us through the day, reminding you that you went upstairs 27 times, tracking our training, checking our heart rate, confirming its raining… and that’s why you are drenched!

What about a gadget for weight management? A new electronic device called Lumen ( has arrived, via the Indiegogo funding platform and is now out in the wild. We have a test unit to hand and we will be trying it in due course, out but in the meantime, here’s some background into what it is and how it works.

What is Lumen?

Lumen is a portable device designed to accurately measure metabolism. Lumen uses a CO2 sensor and flow meter to determine the CO2 concentration in a single breath. This measure indicates the type of fuel your body is using to produce energy. Daily use of the little device in conjunction with the partnering app allows you to monitor, plan and control how your body is fuelled and what the body is using for fuel to accurately maintain a desired body weight or used to safely control weight by ensuring the body is burning the fat stored in your body.


Putting on weight

Putting on weight by the build up of excess fat is a pretty simple process. We gain weight when excess carbohydrates, proteins, alcohol or sugar in the body are converted into triglycerides and stored in fat cells throughout the body. The more we consume above our individual daily calorie requirements, without reasonable activity to burn off the extra calories, will get stored in the body.

As a guide, men need around 2,500kcal (10,500kJ) a day to maintain a healthy body weight, and women need around 2,000kcal a day (8,400kJ). Embarking on a strenuous training plan will of course mean you need to increase your calorific intake to fuel this extra activity.

Metabolism and your weight

Metabolism is the process by which your body converts the food you consume into energy for immediate use or to be stored for later. If you store more than you burn then typically you gain weight.

What are Metabolic fuels?

Your body relies on three main sources of energy:

  • Carbohydrates – Quickest and easiest to produce energy from.
  • Fats – Harder to produce energy from, but provides long, sustainable energy.
  • Proteins – Not a major source of energy as the body uses them primarily as building blocks.

Our carbohydrate storage is the chief regulator of energy in the body.

Fat is one of six nutrients your body needs, along with carbohydrates, proteins, minerals, vitamins and water. Of these six nutrients, carbohydrates, protein and fats provide calories. We need fats, but too much fat being stored will lead to weight gain.

  • One gram of carbohydrate and protein yields 4 calories/gram.
  • One gram of fat yields 9 calories/gram.

As you can see, fat has twice the calorie count of carbs and proteins. To lose weight, you need a calorie deficit. One way you can achieve this is by eating less, consuming fewer calories and exercising.

What happens to fat?

When you lose weight, where does the fat actually go? Traditionally it was believed that fat was burned and converted to energy and heat or even converted into muscle mass. Recent research indicates that your lungs are the primary organ involved with fat loss and getting it out of the body in a process that converts the fat into a form that can be easily exhaled.

Essentially, you breath out converted fat with CO2 with each breath. It should be noted that resting respiration is not going to get you lean by itself! You will need to exercise and raise your metabolism to get your body into a state where it will convert the trapped fat to be exhaled by your lungs. The water formed may also be excreted in the urine, faeces, sweat, breath, tears etc. There a many articles available from trusted sources that go much deeper into the science if you need further reading.

How can Lumen work with you to help you lose weight by measuring metabolism ?

There are two main ways to measure your metabolism:

RQ – Respiratory Quotient. Normally in a hospital/clinic with a costly and time-consuming test known as Respiratory Quotient, which is a measurement through the blood.
RER –  Respiratory Exchange Ratio. Measured through analysing the breath.

Lumen uses RER as the core data point to bring the same measurement to a home environment, by measuring the CO2 in your breath through the sensor and flow meter, based on your RER metric. The CO2 concentration is measured using breath analysis, which is performed by inhaling a fixed volume of air through the Lumen device (dynamic to each individual), holding it for 10 seconds, and exhaling fully. You repeat this process at various points in the day so the device can get an accurate understanding of your body situation.


Metabolic flexibility means being flexible and able to alternate between using fats and using carbs as sources of fuel. This leads to sustainable weight loss, optimised workout performance, or weight maintenance. Healthy individuals can switch between their fuel sources, but better metabolic flexibility allows your body to do so more efficiently and quickly.

You have the ability to improve your metabolism through what you eat and your lifestyle habits. Each morning, Lumen determines the source of your body’s fuel — carbs or fats. Lumen provides personalised nutrition recommendations and daily guidance on sleep, diet, exercise and more.

In multiple studies, Lumen’s patent-pending technology was deemed to accurately measure metabolic fuel usage through analysing your breath when compared to the gold standard RQ (blood) for measuring metabolism. This testing is done in realtime at various parts of the day.

  • Low-carb diet, the body tends to use mainly fat storages as its primary fuel source, which is represented by a low RER.
  • High-carb meal, the body tends to use less fats for fuel, which is represented by a higher RER. Additionally, following a high-carb meal, the body tends to use available carbs in the digestive system, represented by a higher RER.


When using the Lumen device to assess changes in metabolic fuel usage, Lumen can reproduce the same trends described in widely accepted literature. The Lumen technology was found to effectively differentiate between different metabolic states of its user.

In a nutshell the Lumen device can accurately analyse the characteristics of your exhaled breath, suggest a daily diet and activity plan to help you fine tune your nutrition and weight management through a measurable scientific process.


We are testing out a unit right now, so we will report back with our findings.

Written by
Andy Tomlinson


In episode 1 of our new SBRX Show we sit down with ultra runners and coaches Kim and Jayson Cavill to get their take on the Barkley Marathons and triathlon & trail running gear reviews, training tips and more
Discover more
Sumarpo vanguard vs Zone 3 Vanquish X triathlon wetsuits
ZONE3 Vanquish X wetsuit vs Sumarpo Vanguard wetsuit – how do these triathlon wetsuits match up?
Essential Beginner's Triathlon Gear & KIt
Triathlon gear for beginners: essential kit for getting started
open water swimming Sumarpo wetsuit
How to improve swimming endurance – PRO tips to help you swim further in open water
sumarpo triathlon swimming wetsuit
Wetsuit buying guide – How to choose the best wetsuit for triathlon, open water swimming, SwimRun and cold water
Aviles Duathlon
What is a duathlon? Beginner’s guide to distances, training plans and kit
latest News
Gustav Iden Kona athlete sign in 2022 photo credit Donald Miralle for IRONMAN
Gustav Iden shares heartfelt message after major milestone on the journey back to the top
Sam Long celebrates at the San Francisco T100.
Sam Long targeting two major T100 races after season break to resolve personal problems
Challenge Geraardsbergen 2023 - Photo Credit José Luis Hourcade
British triathlon star Joe Skipper looking to save season with big results Down Under
Braden Currie wins IRONMAN Cairns 2019
Long course triathlon legend looking to kickstart season on happy hunting grounds in Cairns
lionel sanders wins oceanside 2024 [Photo credit: Donald Miralle / IRONMAN]
Lionel Sanders set for triathlon return after being announced on start list for event he loves
triathlon on your terms
Never miss out with our triathlon alerts & digest. Get a dose of adventure & inspiration with Boundless.
Invalid email address
The SBRX Group

Proudly elevating endurance sports through content, products & services

Share to...