How far low-calorie diets are effective?

More than you think. The health benefits of low-calorie diets have a lot of science behind them. Recent animal research has shown that low calorie intake over an extended period of time decreases metabolic turn-over, possibly increasing life expectancy. Also, a new study out of denmark showed improved arthritis scores in patients who went on a <1200 cal/day diet over 4 months. Eat healthy!
Not that far. Like all diets, the low calorie diets will initially provide rapid weight loss. The problem is that the body quickly recognizes that it is in starvation mode and the resting metabolic rate slows down greatly. The body becomes far more efficient at extracting calories from all kinds of foods and people begin to regain weight very easily. Please change your lifestyle and eating habits. Don't starve!