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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. Frederick Scwatka's diary described Ketoadaptation this way:

"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."[1]

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.

1 Achieving Ketoadaptation

  • Adaptation typically takes a couple of weeks, but four weeks might be required for all adaptations.
  • An initial 24 hour fast may help, and is recommended for children starting the Ketogenic Diet for Epilepsy.
  • Take the Ketogenic Diet Supplements. In the early stages is particularly important to keep water and salt intakes high, and broth is often recommended.
  • Failure to keep Net Carbohydrates and Protein intakes low enough will prevent Ketoadaptation.
  • Measuring Ketones is critical to make sure your diet is achieving Ketosis.
  • Expect to feel weak and Glycogen depleted during Ketoadaptation. Impaired mental functioning during Ketoadaptation is likely to be worse than a typical low fat diet.

2 Adaptations and Timeframe

The scientific evidence around Ketoadaptation is limited as most studies use obese individuals that are undergoing a prolonged fast rather than a Ketogenic Diet.

  • Ketoadaptation generally takes a minimum of two weeks, but some aspects may take longer. There is an initial phase of a few days that involves weight loss, mostly from Glycogen/water with some muscle loss, but little fat reduction.
  • Ketoadaptation generally requires a reduction in the availability of glucose. This is primarily due to a reduction in the Net Carbohydrate intake, but because the body will convert protein to glucose, the intake of protein must also be controlled.
  • There is a reduction in Glycogen, both Muscle Glycogen and liver glycogen. This takes a few days depending on exercise levels and is associated with weight loss as Glycogen is stored with water.
  • The levels of blood Ketones rise and the time between glucose dropping and ketones rising might contribute to the Ketoadaptation period. This rise in Ketone levels is probably due to improved reabsorption by the kidneys and reduced usage by muscles[2].
  • The ratio of Insulin to glucagon changes, with insulin levels falling. This may be a mechanism that triggers the generation of ketones, but in some situations ketones can be produced even with elevated insulin.
  • Blood uric acid levels initially rise, before falling to baseline levels after 4-6 weeks. This can cause gout in susceptible individuals.
  • The ratio between the Ketones AcAc and BOHB appears to change with adaptation.
  • During Ketoadaptation the kidneys conserve ketones by reabsorption.
    • Studies show that urine ketone excretion generally peaks after 4-8 days of fasting, and then diminishes[3].
    • In fasted obese patients the rate of ketones (AcAc & BOHB) reabsorption increases 5x after 3 days and a further 2-3x increase from day 3 to days 10-24.
    • The reduction in ketone excretion may be linked to the Protein sparing effect of the ketogenic diet.
    • Because most studies of ketone reabsorption by the kidneys use fasting subjects it is unclear if the increased reabsorption is due to a change that occurs over time or due to the increased levels of blood ketones that naturally rise with prolonged fasting.
  • Changes in protein metabolism and nitrogen conservation appear to occur within the first few days. For the first few days protein (muscle mass) is lost, but then stabilizes. Muscle mass can be maintained on a remarkably low protein intake when on the Ketogenic Diet.
  • There are changes in ketone blood/brain barrier, and while the brain will use ketones if they are available, the ability to transport the ketones from the blood into the brain may improve over time.
  • Ketoadaptation can involve greater impaired memory functioning than subjects on a typical fat diet[4]. Ketoadaptation can produce increased confusion, though this is slightly less than subjects undergoing a typical low fat diet[4].
  • The fuel usage of muscles changes with Ketoadaptation.
    • In sedentary obese individuals on a 24 day fast the forearm muscles reduced the uptake of glucose, increased the intake of ketones (both AcAc and BOHB), and increased the intake of fatty acids[5].
    • Some, but not all, studies have shown that muscles will produce Ketones from free fatty acids.

3 Loss of Adaptation

There are no indications of how long it takes to lose Ketoadaptation.

4 See Also

5 References

  1. 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–
  2. 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 6986618
  3. DG. Sapir, OE. Owen, Renal conservation of ketone bodies during starvation., Metabolism, volume 24, issue 1, pages 23-33, Jan 1975, PMID 234169
  4. 4.0 4.1 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 10.1016/j.appet.2008.08.009, PMID 18804129
  5. OE. Owen, GA. Reichard, Human forearm metabolism during progressive starvation., J Clin Invest, volume 50, issue 7, pages 1536-45, Jul 1971, doi 10.1172/JCI106639, PMID 5090067