Grapefruit Diet: This diet has been around since the 1930s and is still going strong. This fast all day slimming tea method is meant to be used for 12 days. This diet is very restrictive, if food isn't allotted in the diet it isn't allowed at all. This is a diet that said to help you lose weight through the ingestion of the unsweetened grapefruit juice. The truth is that you reduced calorie intake and this will encourage weight loss. There isn't a specific reason the grapefruit works other than it is a extremely nutritious and a low-calorie fruit.