Very low calorie diets work, because rapid weight loss is very motivating. Seeing weight pour off you, makes the deprivation of dieting worthwhile. In general, the faster the weight loss the better – because quick weight loss keeps you dieting. Quick weight loss only happens on very low calorie (500-1000) diets, so you need a structure to keep your calories low – whether it is Bars, Formula, prepackaged meals, fast food burgers – whatever works for you.