The short answer to this question is yes. It works simply because there is a reduction in calorie intake. The grapefruit diet has been around for many years but is really what is known as a “fad” diet because there is no scientific evidence to back up its claims. There is much anecdotal evidence in support but claims of grapefruit containing a marvellous fat burning enzyme are simply unfounded in science.

The grapefruit diet, which can be known under different names, basically involves a large reduction in calorie intake with some grapefruit thrown into the mix. Sometimes down to 800 calories only per day are allowed so naturally weight loss will follow. It is a short term diet created to ensure fast weight loss and claims amazing results. It is very restrictive so it is difficult to imagine anyone being able to stay on it for a long period of time. Much of the weight loss achieved is actually a loss of water and once normal eating habits resume so to does the water content in the body and consequently the weight.
The longevity of the grapefruit diet can be put down in large part to the human condition. It comes across as a miracle diet with the grapefruit being an amazing gift of nature containing wondrous “fat-burning powers. There is no doubt that grapefruit are indeed, like most fruit and vegetables, true gifts of nature with health giving properties but they need to be included as a part of an individuals balanced diet. The diet would, like any diet, have greater success when coupled with physical activity and balanced nutrition but unfortunately too many people wanting to burn fat and lose weight are looking for magical and easy methods without the hard work. This one has to be dangerous as it is nearly impossible to maintain good nutrition on 800 calories a day.

If you wish to try the grapefruit diet then it works like this -

There are different styles of the diet with most promising a 10 pound weight reduction over a twelve day period. If one wishes to continue a two day rest is advised before repeating the diet. Some methods recommend exercise in conjunction with the diet while others do not and there is no provision anywhere for controlling weight in the longer term.
A small range of  foods are required for breakfast, lunch, dinner and at bedtime with black coffee and 64 ozs of water to be consumed during the day. Foods such as eggs, bacon, unlimited meator fish, salad with dressing, vegetables (except starchy ones) are eaten at mealtimes with half a grapefruit or 8ozs grapefruit juice at each meal. You can eat as much butter and salad dressing as you want and foods can be cooked in any manner including frying. No snacks until after dinner, grapefruit juice must not be sweetened and no foods or drinks not on the diet are to be eaten.

The grapefruit diet is a low calorie diet and so most people will lose weight whether grapefruit is included or not. While there is no scientific studies to show if grapefruit has any fat-burning powers there is some speculation that because it has a low glycemic index combined with low calorie levels and high fibre it may lower insulin levels to the extent that participants don't feel hungry and as a consequence eat less resulting in weight loss.