The diet variations came into fore based on how active the person is. For instance, a software programmer is not as active as a construction worker. So while a software programmer can limit to 500 calories a day, the construction worker obviously burns more calories and hence needs more than 500 calories because he has a much more active lifestyle than the programmer.
Keeping in this mind, diet variations have been created. Also, if a person is under medication or for some reason unable to handle the low calories can increase the calorie intake that would help him/her to lose weight with HCG while limiting the calorie intake.