The goal is to lose fat, not weight.
The ketogenic diet activates your body's natural fat-burning process; it is a strict version of the low carb diet, where the goal is to eat no more than 20 grams of carbohydrates per day.
By following a ketogenic diet you are also improving your energy levels, since overweight, or obese people have much less energy than people who have a healthy body weight.
It should be stressed that obesity is also related to premature aging, so consider fat loss as life insurance.