The length of time to fast depends on the type of fasting and individual health goals. Common fasting durations include:

• Intermittent fasting with shorter fasts of 12 to 16 hours daily, often recommended for beginners or daily routine, such as the 16:8 method where fasting lasts 16 hours with an 8-hour eating window.
• 24-hour fasting done once or twice weekly can aid weight loss, improve metabolism and cardiovascular health.
• Longer fasts such as 48 hours may provide enhanced cell repair, reduced inflammation, improved insulin sensitivity, and weight loss benefits but should be done less frequently (1-2 times per month) and with caution due to potential side effects like dizziness or fatigue.
• Extended fasts lasting 5 to 30 days are done under medical supervision for more profound health benefits or therapeutic purposes but carry more risks.

For most people, starting with shorter fasts of 12-16 hours is safe, progressing to 24-48 hours if desired with proper hydration and medical guidance. Fasts longer than 72 hours should only be done with medical supervision.