No, it is not healthy, It lacks the nutritional requirements for good health. These type of diets usually lead to high amounts of muscle and water loss and lead to rapid weight gain in the form of fat once the "diet" is over.
The Lemonade diet is also known as the "Master Cleanse"
http://heath-fitness-training.blogspot.com/2009/10/lemonade-diet-maste r-cleanse.html

