Lumen: Fat Loss Hack Or the Next Great Gimmick?

What is Lumen? It’s a device you breathe into that tells you whether your body is burning more carbohydrates or fats, and in theory tells you the exact percentage of carbohydrates or fat your body is burning. 

The concept behind this device is that if you measure what your body is burning you can optimize fat burning and weight loss. 

At least that is what is marketed to us. 

But what is the actual science behind this device? Does it work? How accurate is it? Does it actually help for weight loss? 

Let’s explore these questions by reviewing the core concepts surrounding Lumen: how it works and how accurate it is. Including the actual science behind Metabolic Flexibility, and whether this can help us lose weight and body fat faster.

Lumen: Fat Loss Hack Or the Next Great Gimmick?

How Lumen Works and Its Accuracy

Lumen works based on a well-known concept in physiology and medicine: gas exchange.

Gas exchange is in fact one of the most accurate ways to measure our actual energy expenditure and whether our body is burning carbohydrates or fat. This method is known as indirect calorimetry.

While the details of this are a bit complicated it essentially works by measuring the amount of oxygen you consume and CO₂ you expend, and the ratio between them. Since our metabolic pathways that burn carbohydrates for fuel and fat for fuel have different rates of oxygen consumption and CO₂ production, we can accurately determine how many calories we are burning and what percent of the energy we are burning comes from fat or carbohydrates. 

In lab settings with specialized equipment that measures both oxygen intake and CO2 being expelled this is determined by the following equation:

The exact details here are not important but carbohydrate requires less oxygen than fat metabolism. So higher values mean more carbohydrates are being burned for fuel and lower values mean more fats are being burned for fuel. 

This usually is measured on a scale of 0.7-1.0 where a 0.7 is 100% fat being burned and a 1.0 means 100% carbohydrates are being burned. In most real-world settings we float between these numbers based on our physiology and our activity. 

Ok… so that is how state-of-the-art lab equipment works. But how does Lumen actually work and how accurate is it?

Well Lumen is a small, portable device that only measures CO₂. So even without doing direct comparisons we know that it can ONLY be used to measure relative changes, not absolute amounts. This is verified in studies.

So Lumen can tell you if you are burning more or less carbs… and may give you some insight into your body’s Metabolic Flexibility. But realistically it’s just going to tell you what you recently ate or how hard you are exercising since there is no real “absolute” amount you can measure given there is no O2 uptake measures.

Metabolic Flexibility

In essence, Lumen will simply tell you how much your metabolism changes when you consume carbohydrates or exercise.  This concept, as mentioned above, is usually called Metabolic Flexibility which refers to your body’s ability to switch between carbohydrates and fat to provide energy. 

At baseline (rest and metabolically healthy) our bodies burn mostly fatty acids for energy. As we either increase exercise intensity or eat carbohydrates our bodies will increase carbohydrate oxidation and in some cases decrease fat oxidation. Now note that this does not mean you burn less body fat.. you just temporarily shift the calorie source for ATP production. Conversely, if you consume a higher fat meal or diet you will have lower carbohydrate oxidation and higher fat oxidation. Again, this does not mean you are burning more body fat… just more calories come from fat at that exact point in time.. 

Our ability to switch between carbs and fat can be impaired, meaning we can become less Metabolically Flexible. There are two major things that decrease our body’s Metabolic Flexibility:

• The first is carrying excess body fat and becoming insulin resistant.
• The second is adopting a very high fat diet, not kidding.

Our Metabolic Flexibility can be improved by a few things:

• Exercise
• Weight Loss
• A macronutrient balanced diet

Is Lumen Useful For Weight Loss?

Put simply, not really.

Knowing your substrate metabolism at a given time won’t help you lose weight or meaningfully improve your health. Especially if you are relying on data that just gives you relative changes and not any insights into absolute changes.

So what is the potential utility of a device like this?

A tool like Lumen may help you understand how your metabolism responds to exercise and some foods. However, given its constraints about not measuring oxygen consumption, it probably isn’t going to provide much useful data for most. Furthermore, the people who would really benefit from the type of data it gives (high performing athletes or individuals with medical indications) should go to a laboratory with specialized equipment and pay $100-200 to get a true test done. Then examine their metabolic flexibility across diverse dietary and exercise challenges.