Most healthy adults get benefits from relatively short fasts (12–24 hours), and longer or more extreme fasting should only be done with medical guidance. The “right” length depends on your health, goals, and experience with fasting.

Big picture: how long to fast

  • 12 hours: Gentle entry point (for example, stop eating at 7 p.m., breakfast at 7 a.m.); mainly supports weight control and may slightly improve metabolic markers.
  • 14–16 hours (popular “16:8”): Common intermittent fasting pattern with solid evidence for weight loss and better blood sugar control in many people.
  • 18–20 hours: A bit more advanced; sometimes used for stronger metabolic effects, but hunger, tiredness, and brain fog are more common.
  • 24 hours: Often called “one‑day fast” or “eat‑stop‑eat”; usually done no more than 1–2 times a week.
  • 36–48 hours: Prolonged fasting, typically 1–2 times per month at most, not for beginners; can enhance fat burning and certain cell‑repair processes but has more side‑effect risk.
  • 3–5 days or longer: “Extended” or “water‑only” fasting; research suggests powerful metabolic changes, but this should be medically supervised and is not considered a casual wellness practice.

Typical fasting styles (with rough timing)

Method| Fasting length| How often people do it| Notes
---|---|---|---
12:12| 12 h| Daily| Gentle, good starting point.16
14:10 or 16:8| 14–16 h| 5–7 days/week| Most popular, good evidence for weight loss and insulin sensitivity.13
18:6 or 20:4| 18–20 h| A few times/week| More intense; harder to sustain.38
24‑hour fast| ~24 h| 1–2 days/week| Often dinner‑to‑dinner or lunch‑to‑lunch.38
5:2 diet| Very low‑cal 2 days| Weekly pattern| Two days at ~500–600 kcal, not full water fast.5
36–48 h fast| 36–48 h| 1–2 times/month| Only after you tolerate shorter fasts well.78
3–5+ days water‑only| 3–5+ days| Occasional, supervised| For specific medical/research settings.59

How to choose a safe fasting length

Ask yourself:

  1. What is your goal?
    • General health/weight: 12–16 hours is usually enough for most people.
 * Stronger metabolic “reset”: occasional 24–36 hours _after_ you’re comfortable with shorter fasts.

  1. What is your current health status?
    You should avoid or only fast under medical supervision if you:

    • Have diabetes or blood sugar issues, especially on medication.
    • Are pregnant, breastfeeding, under 18, or underweight.
    • Have a history of eating disorders.
    • Take medications that must be taken with food, or have heart, kidney, or serious chronic disease.
  1. What can you realistically sustain?
    A consistent 14–16‑hour fast most days usually beats doing a huge 3‑day fast once and then quitting.

What research and forums are talking about (2025–2026 vibe)

  • Nutrition researchers still focus heavily on time‑restricted eating (like 8‑hour eating windows), especially earlier in the day (for example, 8 a.m.–4 p.m.) for better blood sugar and blood pressure.
  • There’s ongoing interest in fasting‑mimicking diets (5‑day, low‑calorie cycles) that try to get some of the benefits of long fasts without full food abstinence.
  • Online fasting forums frequently emphasize:
    • Start with 12–16 hours and build up.
    • Listen to your body—severe dizziness, confusion, chest pain, or feeling like you might faint means stop and eat, and seek help if it’s intense.

Common community advice: “Don’t chase the longest possible fast; chase the one you can repeat without wrecking your health or relationship with food.”

Simple starter plan (if you’re generally healthy)

  • Week 1–2: Try 12 hours overnight, then 14 hours if that feels easy.
  • Week 3–4: Move toward 16:8 on most days (for example, 10 a.m.–6 p.m. eating window).
  • Later: If you still want more, experiment with one 24‑hour fast now and then, but only if shorter fasts feel fine and you’re not in a high‑stress or heavy‑training period.

Safety and red flags

Stop fasting and eat, and seek medical advice urgently if you notice:

  • Fainting, severe dizziness, chest pain, shortness of breath.
  • Confusion, trouble speaking, or extreme weakness.
  • Uncontrolled vomiting or inability to keep fluids down.

Those are not “normal” fasting side effects and can signal something serious. Bottom line:
For most healthy people, aiming for 12–16 hours of fasting a day, with an 8–10‑hour eating window, is a reasonable and evidence‑supported target; anything longer than 24 hours should be considered “advanced” and ideally discussed with a healthcare professional first.

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