A 24 hour fast can support weight, metabolic, and cellular health for some people, but it also carries risks and is not safe for everyone.

Quick Scoop

  • Potential benefits:
    • Improved insulin sensitivity and blood sugar control.
* Short‑term fat burning and modest weight loss, especially if done regularly.

* Activation of cellular repair processes such as autophagy, which may support longevity and reduce inflammation.

* Possible improvements in blood pressure and some cardiovascular risk markers in certain individuals.
  • Potential downsides:
    • Strong rebound hunger and increased drive to eat, which can lead to overeating after the fast.
* Reduced tolerance to cardiovascular stress (e.g., dehydration, blood pressure changes) in some people.

* Not appropriate for pregnancy, breastfeeding, certain medical conditions (like some forms of diabetes), eating disorders, or frail individuals.

What actually happens in a 24 hour fast?

  • First hours: Your body uses recently eaten carbohydrates and stored glycogen for energy, and insulin gradually falls.
  • As fasting continues (roughly after 8–12 hours), glycogen depletes and your body shifts more toward burning fat and producing ketones.
  • Later in the fast (around 16–24 hours), cellular cleanup processes and changes in hormones such as growth hormone may increase, which is one reason people link 24 hour fasts to autophagy and “reset” effects.

Research‑linked benefits (with caveats)

  • Metabolic health:
    • Studies of 24 hour or intermittent fasting protocols show reductions in body weight, fat mass, blood pressure, fasting glucose, and triglycerides in some participants.
* A single 24 hour water‑only fast can reduce certain blood markers like TMAO, which is associated with coronary artery disease risk.
  • Inflammation and cellular effects:
    • Repeated 24 hour fasts may reduce inflammatory markers and promote cellular repair, but much of the data is short‑term or from broader fasting patterns.
  • Brain and mood:
    • Some reports and small studies note better mental clarity, focus, and mood during or after a 24 hour fast, possibly related to ketone use and hormonal changes.
  • Appetite and food reward:
    • One interesting finding: a 24 hour fast can make food feel more rewarding afterward, increasing “wanting” and “liking” of food and sometimes increasing intake when you finally eat.

Risks, side effects, and who should avoid it

Common short‑term effects can include:

  • Intense hunger, irritability, headache, dizziness, low energy, and difficulty concentrating, especially in beginners.
  • Drops in blood pressure or reduced tolerance to cardiovascular stress, which may be an issue for people prone to fainting or with heart problems.

People who generally should not do a 24 hour fast unless a clinician specifically supervises it include:

  • Those with diabetes or on blood sugar–lowering medications (risk of low blood sugar).
  • Pregnant or breastfeeding individuals.
  • Anyone with a history of eating disorders, underweight or frail older adults, and people with significant chronic illness unless cleared by a doctor.

Practical pointers (if a doctor says it’s okay)

Health sources and clinicians who discuss 24 hour fasts often suggest:

  1. Build up gradually: Start with shorter fasting windows (like 12–16 hours) and only extend to 24 hours once you tolerate shorter fasts well.
  1. Hydrate: Drink water; some protocols also allow plain black coffee or unsweetened tea to reduce hunger and support alertness.
  1. Choose your day: Many people find it easier to fast on a relatively calm day or on a predictable workday; others prefer a rest day—this is very individual.
  1. Break the fast gently: Avoid a huge, heavy first meal; start with a moderate, balanced plate (protein, some healthy fat, and easily digestible carbs) to reduce digestive upset and big blood sugar swings.
  1. Watch how you feel: Stop and eat if you feel faint, confused, very weak, or unwell, and discuss these symptoms with a healthcare professional.

This information is for general education only and is not medical advice. Always check with a qualified health professional before starting a 24 hour fast, especially if you have any medical condition or take medications.

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