How to boost your metabolism (WebMD)
Drink More Water
The body needs water to process calories. If you are even mildly dehydrated, your metabolism may slow down. In one study, 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 or other unsweetened beverage before every meal and snack. In addition, try munching on fresh fruits and vegetables, which are full of fluid, rather than pretzels or chips.