Is Prolonged and Intermittent Fasting Safe?

A doctor named Alan Goldhamer supervises patients through therapeutic fasting that lasts between 5 and 40 days. has reported ZERO deaths from water fasting, after having over 10,000 fasting patients. So, even though numerous adverse side effects can occur with water fasting, the mortality rate is extremely low (1). While I don’t recommend dry fasting or prolonged fasting without doctor supervision, it is highly possible that you could fast for many weeks without it being life-threatening. Prolonged fasts typically end much sooner than planned due to the psychological difficulty of going without food (2) in addition to the physical challenges of feeling hungry and unwell.

During autophagy, the human body is quite literally detoxifying. That said, it is best to listen to your body and break the fast if you start to feel sick. Fasting has significant psychological effects, like the keto diet due to our bodies need for carbohydrates (2). In some cases, people fast for several days or weeks, then safely return to good health upon breaking the fast with mostly water and health foods. In other cases, fasting for long periods of time can have detrimental effects on people’s health. While some studies have shown that multiple-day fasts are beneficial to human health, more research should be done on best practices.

Most people view starvation as an entirely bad thing – even if it means skipping only one meal – thinking it’s just another type of calorie restriction with short term results. While this can be true for fasting, the negative effects of starvation are more likely to occur when you put yourself on a very low-calorie diet (VLCD). One study determined that after 10 weeks of undereating (due to VLCD without fasting), your hormones change and cause you to feel extra hungry for the next year or longer, leading to weight gain in the long run (3).

A 24-hour fast every couple weeks or a daily 16-hour intermittent fast is generally safe for healthy individuals. Intermittent fasting has gained popularity in recent years and has been proven effective for fat loss in many studies (4). Many people find that it feels completely normal to go without food from dinner until the following day at lunch time, which is why the 16-hour fast is usually a good starting point. Some people start with 12 hours, then slowly build up over time to achieve 16-24 hour fasts through practice. Many fasters go beyond the 24 hour mark for days or even weeks to reap the health benefits. However, with the risks associated with prolonged fasting I do not personally recommend it. In fact, a 2017 study shows that intermittent fasting has all the same benefits as prolonged fasting such as weight loss, improved liver function, and glucose homeostasis (5).