Lumen Review: The Science behind Metabolism Tracking + my experience

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Metabolism plays a significant role in weight loss. However, for many people, our metabolism seems like something that is beyond our control. There is a common belief that it’s just something we are “born with” and cannot be changed.

So for people with a poor metabolism, that sucks.

BUT that theory isn’t necessarily true. You can learn more about your metabolism and use these insights to improve the way your body processes food and burns fat.

Lumen is changing how we think about this aspect of dieting and nutrition. It’s a small breathalyzer that syncs with a smartphone or Apple Watch app to tell you if you are burning fats or carbohydrates. Using its technology, we’re able to learn far more about how our metabolism responds to what (and when) we eat. 

Let’s explore what Lumen is and how you can use it to help your metabolism.

Table of Contents

Lumen with phone, wallet, and keys
Size comparison of my Lumen vs my iPhone 11, Ridge wallet, etc.

What is the Lumen?

At first glance, the Lumen looks like an inhaler or e-cigarette vape. However, unlike those devices, when you exhale through the Lumen, it tells you what kind of energy your body is currently burning: fat or carbohydrates.

By understanding which type of energy your cells are burning, you can understand:

  1. How efficient your body is at burning calories
  2. When you should eat
  3. What you should eat

How does Lumen work?

Lumen describes their device as a metabolic tracker. But what really is your metabolism, and how does the Lumen help out?

Metabolism is a critical physiologic process. Our body’s metabolic rate measures how much energy we expend in a particular time. Typically, it’s calculated daily. Metabolism describes a broad set of chemical processes that occur in the body. Per the Mayo Clinic, processes are things like:

  • breathing
  • digesting food
  • cell breakdown
  • cell creation

Each of these processes requires energy, which comes from food. As a result, metabolism is linked with nutrition because it’s powered by food — mostly fat or carbohydrates.

Generally, the body burns carbs (in the form of glucose) because it’s easier and quicker. However, once stored carbs have been used, the body can switch to a new fuel source: fats. The process of switching between both sources is referred to as metabolic flexibility. This metabolic flexibility, btw, is really the key to all-things-Lumen.

Metabolic flexibility is the ability to respond or adapt to conditional changes in metabolic demand. This broad concept has been propagated to explain insulin resistance and mechanisms governing fuel selection between glucose and fatty acids, highlighting the metabolic inflexibility of obesity and type 2 diabetes.

Cell Metab . 2017 May 2;25(5):1027-1036. doi: 10.1016/j.cmet.2017.04.015.

According to Lumen, metabolic flexibility has several positive effects, including:

  • Better health
  • Stronger immune system
  • Easier weight loss
  • Consistent blood sugar level
  • Better sleep 
  • Optimized workout performance

Overall, people with diabetes and obesity tend to suffer from metabolic inflexibility. Exercise has a considerable influence on this process, and there’s also evidence to suggest that diet plays a role too.

But, how does the Lumen metabolic tracker work? It simply measures the CO2 level in your breath. The device can state whether you are burning glucose or fat by taking these levels.

The Lumen measures the respiratory exchange ratio (RER). This compares the ratio of CO2 you exhale vs. the O2 you inhale.

  • RER of 1 = carbs are being burned
  • RER of 0.8 = protein is being burned
  • RER of 0.7 = fats are being burned

But how legit is that all this science? Let’s check below.

Is the science behind Lumen legit?

So what is the science behind the Lumen

As mentioned above, its aim is “measuring metabolic fuel utilization” via a handheld device. The most accurate way we know to measure metabolic rate is with a metabolic cart. These machines are considered the gold standard of measuring:

  1. the carbon dioxide produced
  2. oxygen consumed from breathing.

When these two measures are combined, we can assess metabolic fuel usage, i.e., (carbohydrates vs. fats).

However, metabolic cart machines are expensive, difficult to operate, large, and only available in a clinical setting.

patient on a bike with a metabolic cart machine
This could be you. But hopefully not.

The Lumen was developed to measure metabolic fuel CO2 via a handheld device. A study by San Francisco State University tested the Validity of the Lumen® handheld metabolic device to measure fuel utilization in healthy young adults.

The results of the study were crazy positive. It showed the val