The diet is based on drastically cutting back calories.
The diet is based on taking special pills, powders, or herbs.
The diet tells you to eat only specific foods or foods in certain combinations.
The diet makes you completely cut out fat, sugar, or carbs.
The diet requires you to skip meals or replace meals with special drinks or food bars.
http://kidshealth.org/teen/food_fitness/dieting/fad_diet_tips.html#cat20131