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There are three important [[Ketones]] involved in [[Ketogenic Diet]]s, Acetoacetic acid (AcAc), Acetone, and Beta-hydroxybutyrate (BOHB). Their levels can vary somewhat independently, and the target levels for different results are not well defined. Blood levels of BOHB from 0.5 to around 3-5.0 mmol/L have been labeled 'nutritional ketosis' and levels over 4.0 mmol/L are probably best for treatment of Epilepsy. My suspicion is that there is a "Goldilocks range" of ketone levels, with higher values indicating insufficient protein intake. It's possible that 1.0-1.5 mmol/L of blood BOHB might be ideal for athletes in order to prevent impaired performance.
=Relative Levels=
[[File:KetonesProgressiveStarvation.jpg|none|thumb|300px|Changes in blood ketone levels during progressive starvation<ref name="Cahill2006"/>.]]
=Target Levels=
There are no well-defined targets for Ketone levels at which particular changes occur. The list below is a sampling of the levels I've found used.
* The classic 1983 study by Dr Phinney measured the athletes blood BOHB as 1.28 mmol/L at rest<ref name="Phinney-1983"/>. This makes me wonder if there is a "Goldilocks effect" to ketone levels. Too high may indicate too little protein, and poor glycogen stores, that may impair endurance performance.
* The level required to be ketogenic (hyperketonemia) has been suggested as 0.2 mmol/L measured as the combination of AcAc and BOHB in whole blood as this is slightly above the levels seen in "normal" individuals<ref name="Robinson-1980"/>. Personally, I'd argue this is too low to be considered ketogenic, as this level is seen in people on a high carbohydrate diet after a night's sleep.
* The book "The Art and Science of Low Carbohydrate Living" calls the range 0.5 to 5.0 mmol/L of blood ketones "nutritional ketosis"<ref name="Phinney-2011-p31"/>
=References=
<references>
<ref name="Phinney-1983">SD. Phinney, BR. Bistrian, WJ. Evans, E. Gervino, GL. Blackburn, The human metabolic response to chronic ketosis without caloric restriction: preservation of submaximal exercise capability with reduced carbohydrate oxidation., Metabolism, volume 32, issue 8, pages 769-76, Aug 1983, PMID [http://www.ncbi.nlm.nih.gov/pubmed/6865776 6865776]</ref>
<ref name="Balasse-1989">EO. Balasse, F. Féry, Ketone body production and disposal: effects of fasting, diabetes, and exercise., Diabetes Metab Rev, volume 5, issue 3, pages 247-70, May 1989, PMID [http://www.ncbi.nlm.nih.gov/pubmed/2656155 2656155]</ref>
<ref name="HayBond1967">RW Hay, MA Bond, Kinetics of the Decarboxylation of Acetoacetic acid, Australian Journal of Chemistry, volume 20, issue 9, 1967, pages 1823, ISSN [http://www.worldcat.org/issn/0004-9425 0004-9425], doi [http://dx.doi.org/10.1071/CH9671823 10.1071/CH9671823]</ref>