Luisa Torres, PhD
Luisa is a science communications manager at LifeOmic and neuroscientist and science writer covering topics related to aging, metabolism, and brain health.

Luisa Torres, PhD
Luisa is a science communications manager at LifeOmic and neuroscientist and science writer covering topics related to aging, metabolism, and brain health.


 

Ketosis and its associated fat-burning is what most people who practice intermittent fasting want. But how do you know your body has made the switch from burning sugar to burning fat? You might go by the general guideline and say you’re in ketosis 12 hours after your last meal, but when you want to track the specifics of your own metabolism, using a ketone meter is a better approach.

There are many commercially available devices that can tell you whether you’re burning sugar or fat. If you’re looking to buy one, you might wonder which are the most accurate and consistent. To help you figure it out, LifeOmic conducted a small experiment to see how various devices compare to one another.  

Jump to see what we found and our conclusions.

What we did

12 LifeOmic employees volunteered to do four 24-hour fasts and measure their blood glucose and blood and breath ketones during the process. Prior to starting the fast, they ate a low-carb meal. They made the measurements when they began their fast and after 12, 16, 20 and 24 hours. We then looked at how ketone and glucose levels changed over time and how much measurement difference there was among devices. Each participant used Precision Xtra, Keto-Mojo and KetoSense to measure blood ketones; Biosense, Keyto and KETONIX to measure ketones in breath; and Precision Xtra and Keto-Mojo to measure blood glucose.

Participants used Precision Xtra, Keto-Mojo and KetoSense to measure blood ketones; Biosense, Keyto and KETONIX to measure ketones in breath; and Precision Xtra and Keto-Mojo to measure blood glucose.

What we found

Ketones increased similarly in all blood ketone meters

Ketosis occurs when your body switches from burning glucose— or stored forms of glucose like glycogen— to burning stored fat. This switch occurs around 12 hours into a fast, but it may happen earlier or later depending on your activity level and the carb content of your meals. Your body produces 3 main ketone bodies or ketones: acetoacetate, beta-hydroxybutyrate and acetone. Beta-hydroxybutyrate is the ketone found in blood and it’s what devices such as Precision Xtra, Keto-Mojo and KetoSense measure. As shown below, all three devices showed low ketone levels for the first 12 hours following a low-carb meal. Ketone levels slightly rose by 16 hours and increased significantly by 20-24 hours. 

Blood ketone levels over time following a low-carb meal. Ketone levels measured with Precision Xtra, Keto-Mojo and KetoSense slightly rose by 16 hours and increased significantly by 20-24 hours.

In contrast, ketone levels remained close to zero during a few practice fasts when participants ate a high-carb meal before the fast, and there was no significant increase in blood ketones even at 24 hours (not shown). 

The three blood ketone devices produced similar values and thus appear to have comparable accuracy. 

KetoSense, Precision Xtra and Keto-Mojo produced similar values for fasting blood ketones.


When surveyed after the study, 7 out of 9 participants said they had no preference for any of these devices for ease of use, although some indicated they preferred blood devices that could measure both ketones and glucose. “I did like the ability to check glucose [as well as ketones], so that gives Keto-Mojo and Precision Xtra a slight advantage over the KetoSens,” said one responder.

Biosense appeared to be the most reliable ketone meter for measuring breath ketones 

Keyto, KETONIX and Biosense detect acetone, the ketone body you find in your breath. Biosense measurements showed an increase in breath ketones that matched the pattern we observed with blood devices, though not as closely as the blood devices agreed with each other. Breath ketones as measured with Biosense were low for the first 12-16 hours following a low-carb meal, but they increased significantly by 24 hours. Keyto’s measurements loosely matched the progressive increase in ketones we observed in blood devices, detecting an increase in ketones at 24 hours (note that Keyto uses a different measurement scale than Biosense). In contrast, KETONIX did not detect the expected increase in ketones, measuring low ketone levels even at 24 hours. Based on this data, we conclude that Biosense is the most reliable device for measuring breath ketones, and that KETONIX does not appear to reflect ketosis at all.

Breath ketone levels over time following a low-carb meal. Biosense measurements showed an increase in breath ketones that most closely matched the pattern we observed with blood devices.

User surveys also found that Biosense was the preferred breath ketone meter for user experience, with Keyto coming in second. 

After a low-carb meal, ketone levels increased as blood glucose decreased

Blood glucose is expected to drop during a fast, leading your body to turn to ketones for fuel instead. We found a progressive decrease in blood glucose that tapered off at 20 hours following a low-carb meal as measured by Precision Xtra and Keto-Mojo. This drop coincided with the observed increases in blood and breath ketones.

Blood glucose over time following a low-carb meal. We found a progressive decrease in blood glucose as measured by Precision Xtra and Keto-Mojo.

There was more variation in blood glucose measurements among devices than for blood ketone measurements 

On average, blood glucose measurements differed between Keto-Mojo and Precision Xtra by 10-15 points as shown below. This difference in measurements in blood devices is expected according to current standards for home glucometers. A lab-validated glucose sample that’s 100 mg/dL can range from 85-115 mg/dL with a home glucometer and still be considered accurate under the current guidelines. Other factors that could introduce variability in measurements include environmental factors such as temperature and humidity. Exposure of the sample to air can lead to 10% variance due to evaporation and coagulation. Your hydration and blood iron status can also affect measurements.

Blood glucose measurements differed between Keto-Mojo and Precision Xtra by 10-15 mg/dL, on average.

Conclusions

Biosense is the most reliable and easy to use breath ketone meter 

Biosense measurements most closely matched the pattern of increasing ketones shown in blood devices during a 24-hour fast. We therefore recommend Biosense for measuring breath ketones. In a post-study survey, 4 out of 8 responders said they preferred Biosense over Keyto and KETONIX because it was the easiest to use. 

Occasionally using Biosense with a blood meter might be ideal

Biosense measurements may not be as precise as blood measurements, so using both Biosense and a blood meter may give a more accurate picture of what your metabolism is doing in real-time. This can be useful when you want to compare the effect of different fasting schedules or diets. 

Blood ketone meters that also measure glucose are best

Because blood glucose decreases at the same time that ketone levels increase, choosing a meter that measures both, such as Keto-Mojo and Precision Xtra, can also give you a more complete picture of your metabolism. 

Disclaimer: Biosense and Keto-Mojo are affiliate partners of LifeOmic. We may receive a small commision when you purchase their products through the LIFE fasting tracker or LIFE Extend apps.


Luisa Torres, PhD

I'm a science communications manager at LifeOmic and the editor of this blog. I am a neuroscientist and science writer interested in covering topics related to aging, metabolism, and brain health. I have written for NPR's blogs 'Shots', 'Goats and Soda', and 'The Salt'.

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