Ketones – Fat as fuel adaption

Building an efficient engine should be the goal of any one.  One important concept in the Fat as a fuel is the role of Ketones:
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After a few weeks of keto-adaptation, the muscles convert most of the acetoacetate type ketone body into beta-hydroxybutyrate (BHB) and return it to circulation, as the brain prefers to utilize BHB for fuel.
As time goes on, and the muscles convert more acetoacetate to BHB, the levels of beta-hydroxybutyrate ketones increase, and the acetoacetate levels decrease.
This is important to know because the Ketone stix you buy in the store only test for Acetoacetate, not beta-hydroxybutyrate ketones.  <—IMPORTANT POINT
So the longer you are eating low carb, the less MEASURABLE ketone bodies will show up on the Ketostix. In other words, it will seem like ketosis is slowing. However, at this point, your brain will be happily burning the beta-hydroxybutyrate ketones for fuel, and as long as you stay under your carb sensitivity levels, you will be burning fat for fuel.
Source: The Art and Science of Low Carbohydrate Living (Volek and Phinney) “