No diet is completely "safe". To determine what is safe for your body you would need to see your general practitioner and have tests done to make sure you are being safe on a new diet. All diets deprive yoour body of essential nutrients and replace them with others. The grapefruit diet, in particular, has it's hazards as it is a very low calroie diet and your body needs a minimum of 1200 calories a day just to funtion. If you lay in bed all day, your body uses 1400 calories, the grapefruit diet simply does not afford enough calories to be safe in the long term.