Definitely unhealthy. The human body needs the most basic nutrition supply to maintain normal operation, including calories and various nutrients. If dieting causes the human body not to get the necessary nutrition supply, in order to maintain the most basic operation, the body can only decompose its own muscles and fats and convert them into sugar to supply energy for the body. This process is that gluconeogenesis will affect many parts of the body, and various problems will occur in the body. Including but not limited to decreased immunity, vulnerable to various other diseases, hair loss, and menopause in women. In addition, many people will have low blood pressure and poor physique when dieting, and dieting will be accompanied by a decrease in basal metabolic rate. Once you return to a normal diet, it is easy to get revenge and even get fat. Dieting to lose weight is an unhealthy and ineffective way to lose weight, which is absolutely undesirable. However, if you are heavy at present, you can lose some fat by controlling and improving your diet structure, that is, eat more fruits and vegetables (non-fruit and vegetable juices) with high protein, low calories and high dietary fiber, which are rich in carbohydrates, and don't eat all kinds of junk food and snacks with high calories every day. This can reduce some fat, but the effect is limited.