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When the [[Ketogenic Diet]] is started there is a period where various adaptations occur. There appear to be multiple different adaptations involved, each with its own timeframe. [http://en.wikipedia.org/wiki/Frederick_Schwatka Frederick Scwatka]'s diary described Ketoadaptation this way:<br/><br/>
''"When first thrown wholly upon a diet of reindeer meat, it seems inadequate to properly nourish the system and there is an apparent weakness and inability to perform severe exertive, fatiguing journeys. But this soon passes away in the course of two to three weeks."<ref name="Speth2010"/>''<br/><br/>
This was written during a 3000-mile Artic trek in 1879-80, and the details of the process have been confirmed scientifically. There appear to be at least two main phases:* The first stage is the depletion of carbohydrate (glycogen) which results in a rise in Ketone levels. This usually takes a couple of days or so, but it will vary depending on how much carbohydrate and protein intake is restricted and exercise levels. (Greater exercise and tighter restriction both speed up the rise in ketone levels.) * There is a second, longer period as the body adapts to burning ketones. This typically takes 2 to 3 weeks, and both physical and mental performance tends to be impaired. Personally, I found the mental fuzziness fades much faster than the difficulty exercising. I find that my breathing rate is much higher for a given exercise intensity than before or after ketone adaptation, and my overnight resting heart rate tends to go up during this period.
=Achieving Ketoadaptation=
* Adaptation typically takes a couple of weeks, but four weeks might be required for all adaptations.
<references>
<ref name="Robinson-1980"> AM. Robinson, DH. Williamson, Physiological roles of ketone bodies as substrates and signals in mammalian tissues., Physiol Rev, volume 60, issue 1, pages 143-87, Jan 1980, PMID [http://www.ncbi.nlm.nih.gov/pubmed/6986618 6986618]</ref>
<ref name="Speth2010">author John D. Speth, The Paleoanthropology and Archaeology of Big-Game Hunting: Protein, Fat, or Politics?, date 8 September 2010, publisher Springer, isbn 978-1-4419-6733-6, pages 84–</ref>
<ref name="Sapir-1975">DG. Sapir, OE. Owen, Renal conservation of ketone bodies during starvation., Metabolism, volume 24, issue 1, pages 23-33, Jan 1975, PMID [http://www.ncbi.nlm.nih.gov/pubmed/234169 234169]</ref>
<ref name="Owen-1971">OE. Owen, GA. Reichard, Human forearm metabolism during progressive starvation., J Clin Invest, volume 50, issue 7, pages 1536-45, Jul 1971, doi [http://dx.doi.org/10.1172/JCI106639 10.1172/JCI106639], PMID [http://www.ncbi.nlm.nih.gov/pubmed/5090067 5090067]</ref>
<ref name="D'Anci-2009">KE. D'Anci, KL. Watts, RB. Kanarek, HA. Taylor, Low-carbohydrate weight-loss diets. Effects on cognition and mood., Appetite, volume 52, issue 1, pages 96-103, Feb 2009, doi [http://dx.doi.org/10.1016/j.appet.2008.08.009 10.1016/j.appet.2008.08.009], PMID [http://www.ncbi.nlm.nih.gov/pubmed/18804129 18804129]</ref>
</references>
