fat for fuel, and they mimic the cascade set forth by fasting.
We theorize that the “hanger” and headaches that may occur
during this three- to seven-day period correspond with the
brain’s upregulating of the enzymes required to process
ketones as fuel.
These times are approximations assuming a non-keto-
adapted state.
1 . Depletion of last consumed carbohydrate. (4 to 12
hours)
2 . Depletion of the body’s stored carbohydrate. Recall
that the liver can store about 100 grams of
carbohydrate in the form of glycogen, give or take
depending on body size. (12 to 18 hours)
3 . Decrease in amino acid breakdown to preserve
muscle. (20 to 36 hours)
4 . Breakdown of amino acids for gluconeogenesis. (24
to 72 hours)
5 . Increase in ketone production and utilization. (48 to
72+ hours)
6 . Upregulating of ketone-burning enzymes in the brain.
This takes up to a week but can be shortened by
emptying carb stores faster with high-intensity
exercise, eating an overall lower-carbohydrate diet, or
integrating medium-chain triglycerides, discussed
momentarily. (1 to 7 days)
7 . Enter a state of metabolic flexibility. Here, the
occasional carb meal can be consumed without
interrupting the fat-adapted state, especially when
consumed during or after a workout.