Does Fasting cause Disordered Eating?

Dr. Jason Fung
5 min readJan 24, 2022

Eating disorders such as anorexia nervosa and bulimia, are extremely serious and occasionally fatal diseases. Anorexia nervosa is a psychological condition of distorted body image, where people see themselves as being very overweight, but in truth are dangerously underweight. Because of this problem, they often engage in extreme diets including fasting to lose more weight. In bulimia, people binge and purge. They will eat excessive amounts of food with little or no control. They simply cannot stop themselves. Afterwards, they get rid of the food by purging — usually by self-induced vomiting or laxative abuse. There is often concern that using an intermittent fasting strategy can cause eating disorders. Luckily these concerns are usually misplaced.

There are two important points to keep in mind during this discussion. First, fasting is merely a tool — they can help or hurt depending upon the situation. Think about a knife — in the right hands, under the right conditions, a scalpel wielded by a trained surgeon will save your life. But that same blade, used to stab somebody will also kill them. The tool is identical — a knife. By itself the tool is neither good nor bad. Everything depends upon the circumstances.

The same holds for fasting. The group of people at highest risk of eating disorders is teenaged girls. In the situation of a underweight, malnourished teenage girl, you would not want to recommend anything close to fasting. It may certainly kill them. There is almost no benefit to fasting. But the situation is very different if you are treating a 60 year old man who weighs 400 pounds and has type 2 diabetes,. His risk of anorexia nervosa is virtually zero, and the weight loss may save his life.

The second important factor is that a disease may cause a symptom or behavior, which does not mean that behavior causes the disease. There will be an association between the two, but it does not show causation. For example, if you have an infected toe, it will cause a fever, and you will feel cold. But feeling cold does not cause an infection.

Diseases cause behaviors, but behaviors don’t necessarily cause disease

This is the same thing for obsessive compulsive disorder (OCD) where people…

Dr. Jason Fung

Nephrologist. New York Times best selling author. Interest in type 2 diabetes reversal and intermittent fasting. Founder