In order to maintain a normal body weight, you need enough vitamins and other nutrients. But you need to limit the excessive calories. If you can eat fewer calories, and still get enough vitamins and other nutrients, you will be able to maintain a healthy body weight.
Proper calorie-restriction might help to control your body weight, but getting enough vitamins and nutrients is also very important. Calorie-restriction may help an overweight person to achieve a healthy weight, and it might slow aging process. But this method does not necessarily prolong a person's life, and it may not be safe.