Theoretically, if you eat more than you eat, you can lose weight. There is no requirement for food, so if you eat more, you can lose weight by eating potato chips. But eating grapefruit depends on how you eat it. If you only eat grapefruit mixed with cabbage, you will lose weight, but it is unhealthy. It is best to achieve a balanced nutrition. Vegetables and fruits do not have the nutrition of meat, and the six nutrients of the human body must be ingested every day. You have to eat something, no.