Will breath ketones increase when blood ketones are metabolized?
Posted by Michel Lundell on
No. The conversion between blood ketones (beta-hydroxybutyrate, BHB) and acetoacetate doesn’t happen in your liver. It happens inside the cell that needs the energy, and the cell uses it there and then. So burning BHB adds little or nothing to your breath. Breath acetone comes from the liver turning fatty acids into acetoacetate, which is unstable and decarboxylates to acetone.
(image is just an ai image to illustrate fat metabolized into acetoacetate and acetone)
If you use exogenous ketones (BHB), the BHB in your blood goes up. Rising BHB is a feedback signal that reduces the release of fatty acids from fat tissue (Stubbs et al., Front Physiol 2017). The liver gets less fat to work with, makes less acetoacetate, and your breath ketones can decrease.
Ketones are not a fuel for burning fat; they are a product of burning fat. Breath ketones show that process as it happens. Blood ketones show the feedback that follows it.