how long should i fast

How long you “should” fast depends a lot on your health, experience level, and why you’re fasting; for most generally healthy adults, short intermittent fasts (12–16 hours overnight) are the usual safe starting point, while long fasts of more than 24–48 hours should only be done with medical guidance.

Key idea: there’s no one magic length

• There is no single “best” fasting length that fits everyone; age, medications, medical conditions (like diabetes, eating disorders, pregnancy), and activity level all change what’s safe.

• Almost all experts agree: if you have any chronic condition, take regular medications, are pregnant/breastfeeding, underweight, or have a history of disordered eating, you should speak with a clinician before fasting longer than an overnight fast.

Common fasting lengths

12–14 hours (very beginner‑friendly)

• Often done by just not eating between evening and breakfast (for example, stop at 7 p.m., eat at 7–9 a.m.).

• This window is often suggested as an easy starting point and can fit into normal life while still potentially supporting weight management and metabolic health for some people.

16 hours (popular “16:8” style)

• Many people eat during an 8‑hour window (for example, 11 a.m.–7 p.m.) and fast the remaining 16 hours; this pattern is frequently used in intermittent fasting research for weight and blood sugar benefits.

• Some sources suggest women may start at 14 hours and only extend to 16 hours if they feel well, while men may tolerate 16 hours from the start.

24 hours (once in a while)

• Some intermittent fasting plans use a full 24‑hour fast (e.g., dinner to dinner) once or twice per week, but this is more intense and not suitable for everyone.

• People are usually advised to build up with shorter fasts first and to stop if they feel unwell (dizziness, weakness, confusion, or heart palpitations).

36–48 hours and beyond (advanced only)

• A 48‑hour fast is often described as the upper end of what most people do on their own, and even then, it is usually limited to once or twice per month at most.

• Fast durations of several days (3–5 days or more) are generally considered “prolonged” and should only be done under close medical supervision due to risks like electrolyte imbalance, low blood pressure, and worsening of hidden health problems.

Safety checkpoints before you fast longer

• Do not attempt long fasts if you are pregnant, breastfeeding, under 18, underweight, or have a history of eating disorders, unless you are in a structured medical program.

• People with diabetes, heart disease, kidney disease, or on blood‑pressure or glucose‑lowering medications need professional guidance, because fasting can change blood sugar, blood pressure, and drug levels.

• Warning signs to break the fast immediately include: chest pain, severe dizziness or fainting, confusion, trouble breathing, or an irregular or racing heartbeat.

Simple rule of thumb

• For most otherwise healthy adults:
  • Start with 12 hours overnight, then, if it feels okay and a clinician has no objections, consider 14–16 hours as a typical intermittent fasting range.

* Treat anything beyond 24 hours as “advanced,” something to approach rarely, carefully, and ideally with medical oversight.

Information gathered from public forums or data available on the internet and portrayed here.