Fasting Duration to Metabolic Switch

Calculate hours of fasting needed to deplete hepatic glycogen and transition to fat-burning (ketosis) based on activity level, recent carbohydrate intake, and metabolic rate.

Weight
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Clinical Guidance

BMI is a screening measure of body size, not a direct measure of body fat. The standard WHO categories are underweight (<18.5), normal (18.5–24.9), overweight (25–29.9), and obese (≥30).

BMI can overestimate body fat in athletes with high muscle mass and underestimate it in older adults with low muscle mass. Interpret it alongside waist circumference and clinical context rather than as a standalone diagnosis.

⚕ Clinical Disclaimer: These calculators are for educational and reference purposes only. Always verify results with qualified clinical judgment and current clinical guidelines. Do not use as a sole basis for medical decisions.
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How It Works

Calculate hours of fasting needed to deplete hepatic glycogen and transition to fat-burning (ketosis) based on activity level, recent carbohydrate intake, and metabolic rate

Each component has a specific meaning:

  • Activity level — The activity level recorded for the scenario being assessed.
  • Recent carbohydrate intake — The recent carbohydrate intake recorded for the scenario being assessed.
  • Metabolic rate — The metabolic rate recorded for the scenario being assessed.

Note: Interpret the fasting metabolic switch result against the thresholds and context described above.

How to Use

Enter the activity level, recent carbohydrate intake, metabolic rate for the scenario you are assessing. Calculate hours of fasting needed to deplete hepatic glycogen and transition to fat-burning (ketosis) based on activity level, recent carbohydrate intake, and metabolic rate. Use the fasting metabolic switch result to inform your calculation.

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Frequently Asked Questions