Please note that I am not a doctor and the following is not a substitute for professional medical advice. If you are considering drinking only water and not eating (i.e. water fasting or starving) to lose weight quickly, be sure to consult a professional medical staff before implementing it to ensure that your physical condition is suitable for doing so. There is actually no unified answer to the "optimal duration" because it depends on the individual's health status, physical foundation, lifestyle and purpose of fasting. Here are some key points to consider: 1. Health risks: Long-term or extreme water fasting may lead to hypoglycemia, dehydration, electrolyte imbalance, hypotension, malnutrition and other potential health problems. Many experts warn that metabolic disorders and overeating are prone to occur after long-term fasting, which is not good for the body. 2. Common fasting methods: Many fasting methods (such as intermittent fasting) usually only do not eat during a certain period of time every day (such as the 16/8 method, that is, fasting for 16 hours a day and eating for 8 hours), or arrange 1 to 2 days a week for a shorter period of low calorie intake, rather than drinking only water for one day. These methods have shown certain benefits for metabolic health in some studies, but they also require individual adjustment. 3. Individual differences: If you only drink water for one day, some healthy people may not encounter major problems in an occasional short-term water fast, but for some people with chronic diseases, hypoglycemia, immune system problems or other special conditions, this method may be riskier. In addition, everyone's tolerance to fasting is different, whether it is 24 hours or longer, it should be adjusted according to the body's response. 4. Professional supervision: If you plan to extend the water fasting time (for example, more than 24 hours to several days), it is best to do it under the supervision of a doctor or professional nutritionist so that you can monitor your physical condition and adjust the plan in time. In general, for many people, a one-day water fast (that is, drinking only water for 24 hours) may be considered a short-term attempt in some cases, but it is not a long-term or sustained weight loss strategy. If your main goal is to lose weight and improve your health, it is usually recommended to adopt a balanced diet, moderate exercise, and possible intermittent fasting programs, rather than relying solely on complete fasting. Summary: There is no "optimal duration" that applies to everyone. Just one day of water fasting may be relatively safe for some people, but if you plan to implement this method for many days or frequently, the risks will increase significantly. Be sure to speak with a medical professional before considering this to ensure that the plan is appropriate for your physical condition and is focused on long-term health rather than simply pursuing quick weight loss.