Body stages Stage 4 of 11
18–24 h
Ketones rising
In studies of healthy adults, blood ketones usually pass the nutritional ketosis threshold around 18 to 24 hours. Timing varies from person to person.
What studies measured
Blood BHB crosses 0.5 mmol/L at a mean of 21 hours, SD 3 hours; earlier with exercise.
How it may feel
Some people notice a lighter, clearer feeling; others notice nothing.
What to do
Include a sodium source from here on. Keep activity light.
Sources
- Deru 2021The Effects of Exercise on β-Hydroxybutyrate Concentrations over a 36-h Fast: A Randomized Crossover Study. Med Sci Sports Exerc, 2021.
- Service and O'Brien 2005Increasing serum betahydroxybutyrate concentrations during the 72-hour fast: evidence against hyperinsulinemic hypoglycemia. J Clin Endocrinol Metab, 2005.
What studies measured in healthy adults, not a reading of your own body. Stop and seek help if you feel unwell; the signs to stop for are listed under Stop signs on the safety page.