How Often Should You Do a 24-Hour Fast?

If you’ve ever experienced the clear-headed energy that comes after a day of fasting, you’ve likely wondered—how often should you do a 24-hour fast?

The answer depends on your goals, your current metabolic flexibility, and your unique hormonal stage of life. But before we talk frequency, let’s look at why a 24-hour fast can be such a powerful reset for your body and brain.

What Happens During a 24-Hour Fast?

At around 17–24 hours without food, your body shifts into a state called autophagy—a process where cells recycle damaged parts, remove toxins, and make themselves stronger.Japanese cell biologist Dr. Yoshinori Ohsumi won the 2016 Nobel Prize in Medicine for his discovery of this cellular process, showing how fasting triggers our innate self-healing design.

A 24-hour fast gives your body enough time to:

• Activate autophagy, clearing out cellular debris and damaged proteins

• Lower insulin and improve insulin sensitivity, reducing inflammation and blood sugar swings

• Increase ketone production, providing your brain with a cleaner, steadier fuel source

• Support mitochondrial health, which boosts energy and cognitive function

  
  

A review published in Cell Metabolism confirmed that fasting and time-restricted eating improve blood pressure, reduce oxidative stress, and enhance insulin sensitivity in overweight individuals.

How Often Is Optimal?

From my clinical experience and the emerging science, here’s what I’ve seen work best:

• Once a week: Ideal for metabolic flexibility and gut reset. I call this a “gut reset fast” in Fast Like a Girl. It’s a gentle way to activate autophagy without overwhelming your system.

• Once a month: A great rhythm for women during perimenopause and menopause, when longer fasts often bring sharper mental clarity and better glucose regulation.

• Quarterly or biannually: For a deeper cellular clean-out, do a 24-hour or even 36-hour fast a few times a year. Many women in my Reset Academy find that pairing these fasts with lifestyle changes (circadian alignment, clean eating, and stress reduction) amplifies results.

  
  

If you’re ready to try a guided fasting experience, join me for Fast Training Week — a five-day FREE experience where we cycle through different fasts to activate specific healing pathways like fat burning and autophagy.

In other words: think of fasting as a tool you rotate through the year, not an everyday event.

What the Science Says

• A 2019 review in Nutrients found that intermittent fasting improves markers of metabolic health, including glucose regulation and fat oxidation.

• A 2021 review in Frontiers in Endocrinology linked intermittent fasting to improved sleep quality and energy, likely due to better circadian gene expression.

• A 2022 study in Cell Reports demonstrated that even short-term fasting enhances autophagic recycling and mitochondrial function in human skeletal muscle.

• Research from Dr. Valter Longo at the USC Longevity Institute shows that fasting not only improves immune health but prompts the body to replace old, damaged cells with new, efficient ones.

These findings highlight that fasting is not simply about calorie restriction—it’s about activating your body’s innate repair system.

Should Women Fast Differently?

Absolutely. Women’s hormones change how the body responds to fasting.

• Cycling women should align longer fasts with the follicular phase (Days 1–10 of the cycle).

• Postmenopausal women can safely explore longer fasts—like 24 hours or more—since they’re no longer cycling through estrogen and progesterone fluctuations.

  
  

Research and lived experience show that postmenopausal women often experience an incredible boost in brain clarity during longer fasts due to the rise in ketones, which serve as an alternative fuel source for the brain when glucose sensitivity declines.

How to Prepare for a 24-Hour Fast

1. Start small – Begin with 13- to 16-hour fasts several times per week.

2. Stay hydrated – Add electrolytes or minerals to your water.

3. Break it with quality food – Include protein, healthy fat, and fiber to stabilize blood sugar.

4. Sync with your life – Choose lower-stress days; fasting is not ideal during high-stress or high-training periods.

   
   

My Recommendation

Most people thrive by doing a 24-hour fast once a week or once every other week. For deeper healing or metabolic resets, aim for a 24- to 36-hour fast quarterly. If you’re new to fasting, build up gradually and listen to your body—it will tell you when it’s ready for more.

Remember: fasting isn’t punishment. It’s communication. It’s your body’s way of recalibrating and reconnecting you to your natural rhythms.

Key Takeaway

A 24-hour fast can:

• Boost autophagy and stem cell renewal

• Support brain clarity through ketone production

• Improve insulin sensitivity and inflammation

• Reset your microbiome and metabolism

But the right frequency depends on your stage of life and your body’s readiness. As I always say, fasting is a healing tool, not a competition.

References

1. Ohsumi Y. Autophagy: from phenomenology to molecular understanding in less than a decade. Nat Rev Mol Cell Biol. 2017.

2. Longo VD, Panda S. Fasting, circadian rhythms, and time-restricted feeding in healthy lifespan. Cell Metab. 2016.

3. Jamshed H, et al. Early time-restricted feeding improves 24-hour glucose levels and insulin sensitivity. Cell Metab. 2019.

4. de Cabo R, Mattson MP. Effects of intermittent fasting on health, aging, and disease. N Engl J Med. 2019.

5. Patterson RE, Sears DD. Metabolic effects of intermittent fasting. Annu Rev Nutr. 2017.

6. Longo VD, et al. Fasting-mimicking diet and markers/risk factors for aging, diabetes, cancer, and CVD. Sci Transl Med. 2017.