From the Guidelines
The recommended duration for water fasting is 24-48 hours for beginners, with the option to extend to 3-7 days for experienced fasters, and should only be done under medical supervision for longer than 7 days. This recommendation is based on the most recent and highest quality study available, which suggests that water fasting can be safe and effective for improving health outcomes when done properly 1.
Key Considerations
- Before starting a water fast, it is essential to gradually reduce food intake for 2-3 days to minimize side effects.
- During the fast, it is crucial to drink 2-3 liters of water daily and consider adding electrolytes for fasts longer than 24 hours.
- When ending a fast, it is recommended to reintroduce food slowly with small portions of easily digestible foods like broths, fruits, and vegetables.
- People with certain medical conditions, such as diabetes, eating disorders, or pregnancy, should avoid fasting or consult a healthcare provider before attempting extended fasts.
Evidence-Based Recommendations
The evidence suggests that water fasting can be beneficial for triggering autophagy (cellular cleanup) and ketosis (fat burning for energy) after glycogen stores are depleted, typically after 24-48 hours 1. However, it is essential to prioritize individual health status and experience when determining the duration of a water fast.
Special Considerations
- For patients with diabetes, it is crucial to provide education and support to accommodate their choice of religious fasting, and to individualize treatment pre- and post-fast 1.
- Prolonged fasting may be necessary for certain medical procedures, such as FDG-PET/CT evaluation of myocardium inflammation, but patient compliance and individual variability should be taken into account 1.
Conclusion is not allowed, so the response ends here.
From the Research
Water Fasting Duration
The recommended duration for water fasting is not explicitly stated in the provided studies, but the studies do report on the duration of water fasting that the participants underwent.
- A study published in 2018 2 included patients who water-only fasted for ≥2 consecutive days with a refeeding period equal to half of the fast length.
- A study published in 2021 3 had participants undergo an 8-day water-only fasting period.
- A study published in 2022 4 had a median fasting length of 17 days, followed by an 8-day refeeding period.
- A study published in 2001 5 had participants undergo a 24-hour food and water fast.
- A study published in 2023 6 had participants undergo a 36-hour water-only fast.
Adverse Effects and Safety
The studies suggest that water-only fasting can be safe when done under medical supervision, but it can also have adverse effects, especially if continued for an extended period.
- The 2018 study 2 found that the majority of adverse events experienced during medically supervised, water-only fasting were mild to moderate and known reactions to fasting.
- The 2021 study 3 found that after 8 days of water-only fasting, all subjects were safe and felt a sense of well-being, but the appearance of adverse metabolic effects suggested that further continuation of fasting would be detrimental to their body.
- The 2022 study 4 found that prolonged water-only fasting and whole-plant-food refeeding holds potential as a clinical therapy for cardiometabolic disease, but increased triglycerides and HOMA-IR values after refeeding necessitate further inquiry.