Ketogenic Diets: Measuring Breath Ketone Levels

By Jason Fung, MD

By Megan Ramos, Clinical Educator and Co-founder of The Fasting Method with Dr. Jason Fung, M.D.





How do you know if your intermittent fasting or ketogenic diet is working well for you? Health tracking devices can enable you to monitor measurements such as glucose and ketone levels, sleep data, fitness and more. The data can provide you with insight into what lifestyle and nutritional strategies are working best for you. Data can also help you shape positive habits, such as cutting out late night snacking. 


One of the most popular biomarkers people ask me about are ketones. But first, what are ketones? They’re an alternative fuel source to glucose (sugar) for the body and are generated from eating a diet high in natural fats or from burning body fat during a fast.  


Many people strive to be in nutritional ketosis, which means the body is being fuelled mainly by fatty acids and ketone bodies rather than glucose. Nutritional ketosis is a natural metabolic state and has been shown to be effective for reversing type 2 diabetes, losing weight, and many more health improvements.  




Members and clients of The Fasting Method strive to be in a state of nutritional ketosis either through fasting, a ketogenic diet, or combining both strategies. Nutritional ketosis is achieved when in a fasted state after the body has used up its glycogen stores, or when dietary carbohydrates are significantly reduced, and the body’s production of ketones increases to maintain a blood level at or above 0.5 mmol/L.  


How can you determine whether or not you’re in a state of nutritional ketosis? When we talk about ketone fuel we are referring to the circulating fatty acid metabolites beta hydroxybutyrate and acetone. You can measure beta hydroxybutyrate by using a glucometer that measures both blood glucose and ketone levels. Acetone levels can easily be measured via breath using a ketone breathalyzer.  



One of the easiest ways to measure ketones is by using a ketone breathalyzer. The Biosense breath ketone monitoring system is the only clinically-backed breath ketone monitor. This device provides you with an easy and accurate way to determine whether or not you are in a state of nutritional ketosis while intermittent fasting or following a ketogenic diet.  


You receive quick feedback directly on the device or on the app available on both iOS and Android platforms. It’s easy to test anytime, anywhere. Users are encouraged to test several times per day, to uncover patterns and trends. You simply turn it on and wait a few seconds for it to prepare to measure your ketone level. Once it beeps you exhale into the mouth-tip for just a few seconds. In less than a minute you can determine whether or not you are in nutritional ketosis.    


Measuring your ketones can help you do more than determine whether or not you’re in nutritional ketosis.  It can also help you stay on track with your intermittent fasting plan or ketogenic diet.



By The Fasting Method

For many health reasons, losing weight is important. It can improve your blood sugars, blood pressure and metabolic health, lowering your risk of heart disease, stroke and cancer. But it’s not easy. That’s where we can help.


Jason Fung, MD

By Jason Fung, MD

Jason Fung, M.D., is a Toronto-based nephrologist (kidney specialist) and a world leading expert in intermittent fasting and low-carb diets.

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