After somewhere between three and five hours, your body stops processing its last meal. There's nothing left to absorb, so insulin levels naturally decrease. Then, somewhere between eight and 12 hours after that last meal, your body starts burning stored fat. (Why don't you start burning fat sooner? Biology is sometimes a pain in the ass; it's like our bodies will do anything to hang on to fat.)
It is important to understand that weight is entirely a function of input and output. The input is the food you eat and the calories contained therein. The output is your energy output. To lose weight the output needs to be greater than the input. It is that simple. Do not believe any of the diet fads. If you are currently not gaining or losing weight then just burning 300 extra calories per week or eating/drinking 300 calories less per week (2 sodas for example or a small burger) WILL make you lose weight - in this case around 5 pounds of fat per year.
Trim Portions. If you did nothing else but reduce your portions by 10%-20%, you would lose weight. Most of the portions served both in restaurants and at home are bigger than you need. Pull out the measuring cups to get a handle on your usual portion sizes, and work on paring them down. Get instant portion control by using small bowls, plates, and cups, says Brian Wansink, PhD, author of Mindless Eating. You won't feel deprived because the food will look plentiful on dainty dishware.
In a way, moderate-intensity physical activity is that "magic pill" a lot of people are looking for, because the health benefits go beyond keeping your waistline trim: Not only can it reduce your risk of cancer, stroke, diabetes and heart attacks, but studies have shown that physical activity can significantly improve the moods of patients with major depressive disorders.