The idea that you can lose fat from a specific body part by working the muscle near it makes no sense because muscle and fat are gained and lost in different ways.
The logic is simple: To help the body lose fat and keep muscle, people have to use more energy than they take in. The reality is that it takes time, and varies depending on age, fitness level, nutrition status and effort.
One way that applies to everyone and that will always lead to positive results is eating healthy and avoiding bad snacks. People tend to forget that every piece of food they consume has calories and ingredients which should be counted towards your total for the day.
Pizza, even tough obvious, is not the only offender. Pretzels, nuts and even smoothies can be very deceiving. Snacks that seem to be loaded with fruits and vegetable may also hide a lot of sugar and artificial ingredients, making them nutritionally empty.