Medical research



Health and Wellness




Breath vs blood ketones.

The short version:
  • Breath ketones indicates that fat is metabolised now and the level of ketosis.
  • Changes in ketosis can be seen in breath ketones within minutes.
  • Blood ketones indicates "reserve" energy and could be viewed as trace of ketosis.
  • Blood ketones levels are important for people having issues metabolising them, e.g people having diabetes.

The higher level of breath acetone, the more blood ketones are produced. However as the blood ketones can be used as energy and/or your body have issues to metalbolize them a correlation is problematic to make.

The little longer version ...

When fat is broken down in the liver a ketone named AcetoAcetate is created. This ketone is used to create energy.

From the AcetoAcetate Acetone is spontaneously released. This means that when liver breaks down fat into energy (AcetoAcetate), Acetone is is released.

Acetone is mainly a waste product, only a small part is used by the body so the majority of the Acetone is discharged from your body by breath.

The liver can not produce the exact amount of energy needed in every moment, so the process of breaking down fat to energy will work with some overcapacity. You can view the level of ketosis as how much your liver works on producing energy. The higher concentration of breath ketones, the more fat is broken down into ketone energy and indication of how much extra capacity that is produced.

The overcapacity that is produced is buffered in your blood as "blood ketones" (Beta-hydroxybutyrate). These blood ketones can be consumed when body needs energy. It can be viewed as a reserve.

This "reserve" of ketones can be converted back to AcetoAcetate and used for energy when your body needs it. If your body have a low level of energy need and glucose and insulin levels indicate that body needs to store energy (after a meal), the process of converting fat into energy (ketosis) decrease . The level of "reserve" (blood ketones) will however not decrease as energy is available from glucose. At this moment body use glucose for energy, ketosis decrease and blood ketones is not used. Measuring breath ketones will indicate low ketosis as breaking down fat is decreased, measuring blood ketones will indicate some level as they are not used.

Breath ketones will tell you the level of breaking down fat (ketosis), blood ketones indicates your level of reserve, not level of ketosis.

High levels of blood ketones can also indicate issues with metabolising them. People with type 1 diabetes are those who needs monitoring blood ketones to not get in to ketoacidosis. Ketoacidosis is a condition when blood sugar is high and the insulin level is low and signals to create ketones for fuel. When blood sugar is high it inhibits the ability to use the blood ketones.

The result is both high blood sugar and a high level of blood ketones which is very toxic for the body. People with working insulin production does not have this issues as the insulin protects your body from high blood and ketone levels.

When body needs energy, blood ketones are one alternative for the body to use. If a person takes exogenous ketones, blood ketones level rise quickly (exogenous ketones are beta-hydroxybutyrate in some form). Breath ketones will decrease rapidly as ketosis will decrease while there is a surplus of ketone energy available in the blood. So having exogenous ketones will increase your blood ketones but not increase your breath ketones as fat is not metabilised into AcetoAcetate in the liver.

The nature of blood ketones being a "reserve" of energy and affected of how well your body can use them makes it hard to correlate blood and breath ketones.

Breath ketones are present when fat is metabolized. Blood ketones are built up from excess production of AcetoAcetate and used when body needs energy.

Measuring blood ketones gives you the status of how much ketone energy that currently is not used.

Measuring breath acetone gives the following advantages: It is not a buffer and is therefore indicating the ketosis process better than blood. Breath acetone varies with the availability of energy (glucose) and insulin. Low glucose (and insulin) will increase glucagon and trigger ketogenesis. The variation of ketosis is noticeable within minutes. This makes breath acetone a superior marker for monitoring how the metabolise fat in almost real-time.

Breath ketones eables one to "see" how body reacts to food and exercise. Using this information enables a user to create a lifestyle where fat is fueling their body.