Water is necessary for optimal metabolism. One study found that adding 1.5 liters of water to the usual daily consumption reduced the average weight and body mass index in a group of overweight women aged 18–23. If you are even mildly dehydrated, your metabolism may slow down.
Another study found that adults who drank eight or more glasses of water a day burned more calories than those who drank four. To stay hydrated, drink a glass of water before every meal and snack. Also, add fresh fruits and vegetables to your diet, as they naturally contain water.