Ketoadaptation

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." This was written during a 3000-mile Artic trek in 1879-80.

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1 Adaptations and Timeframe

• The scientific evidence around ketoadapation is limited as most studies use obese individuals that are undergoing a prolonged fast.
• Ketoadaptation generally requires a reduction in the availability of glucose. This is from a reduction in net carbohydrate intake, but because the body will convert protein to glucose, the intake of protein must also be controlled.
• Ketoadaptation generally takes a minimum of two weeks, but some aspects may take longer.
• There is a reduction in Glycogen, both muscle glycogen and liver glycogen.
• The levels of blood Ketone rise.
• 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 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, then diminishes. (Renal conservation of ketone bodies during starvation)
  • 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.
• Changes in ketone blood/brain barrier.
  • The brain will use ketones if they are available, regardless of the level of glucose in the blood.
• 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. (Human forearm metabolism during progressive starvation.)
  • Some, but not all, studies have shown that muscles will produce Ketones from free fatty acids.

2 Loss of Adaptation

How long does it take to lose the adaptations?