agree with samhradh.
tv3 had a great piece on fad dieting last week - in summary: fad diets cause the body to go into 'starvation' mode, you will immediately hold onto all fat in case of serious crisis and the body will drop fluid and muscle. Once muscle drops the metabolism will slow as it doesnt need as many calories to run less muscle meaning as soon as you eat normally again the number of calories consumed is higher than is needed hence you end up piling on the weight.
Dieting isnt rocket science, eat a clean diet, dont overeat and exercise regularly. To lose weight requires a lifestyle change - not a fad diet.