The principle of eating only tomatoes a day to lose weight is to dehydrate the body by reducing the intake of salt, so as to achieve the purpose of losing weight.
It will cause nutritional imbalance, and the consequence will be weakness. Because protein's intake is insufficient, it will cause anorexia and depression. By the way, the death rate of anorexia is second only to cancer. And once such a diet returns to a normal diet, it will immediately gain weight.
This single diet will damage health due to lack of nutrition and even lead to the crisis of immune imbalance.