Water fasts up to 24 to 36 hours in duration are generally safe and well tolerated based on clinical studies, Dr. Krista Varady says. However, from a weight loss and maintenance perspective, 24-hour water fasting on a regular basis can be difficult to stick to and adopt as a long-term health practice. People with eating disorders should not to practice IF without oversight from a physician. However, alternate day fasting has been found to decrease feelings of depression and binge eating behavior in obese subjects, while improving body image perceptions.
It’s best for your metabolic health to stick to a fasting regimen you can easily maintain over time, with the caveat that you should stop fasting and see a physician if you experience light-headedness or significant discomfort, or if you are at risk of becoming underweight. Intermittent fasting is not the only way to improve your metabolic health; it’s important to find the meal composition and timing plan that works best for you long term.
There is limited research on the impacts or safety of long term periodic fasting for 3-5 days at a time.