When we think loosing weight, we tend to think cutting down on food in general (calorie intake) and exercising to burn more calories. However, this is hardly what the story is all about. It also depends on the quality of food one enters into his body and the timing of meals and of course how one exercises also can make a great deal of a difference.
Some people get more hungry when they exercise and tend to consume more calories than what they burn yet while thinking they will loose weight simply because they exercised. Other people do cardio at a level below or above their THR (Target Heart Rate) believing that they're burning stored fat. Some people fast all day and eat one big meal in the evening thinking that they are dieting when all they're doing is destroying their metabolism and putting their body in a starvation mode (where its brought to burn muscle to survive and accumulate access fat).
To burn stored fat, the rule is you have to do over 20 minutes of a steady cardio activity at your THR (Target Heart Rate), not higher neither lower. Each person's THR differs than the other depending on how long he's been exercising and numerous other factors. Eating breakfast is very important; and it the one meal that you should never miss and during which you can get away with sugars, carbs and almost anything you desire to eat, because your body will be ready to burn the intake after many hours of fasting all through the night. Having breakfast, along with eating small meals every two to three hours along the day is what preserves your metabolism and prevents your body from slipping into the fat storage mode. Spending long hours in the gym and exercising haphazardly may put your body in the catabolic mode (i.e. causing you to burn muscles rather than build them). Even if your goal is not muscle building, each time you loose muscle, you loose a chance to burn more calories effortlessly, because muscles burn calories even while you're asleep; so the motto must always be 'preserve all the muscle mass you can preserve', even if you're a super model striving to be skinny slim. When you do cardio like biking or walking at your THR for more than 2o minutes, your body breaks down old stubborn fat for energy as opposed to just consuming any energy from food or glycogen stored in the muscle area. If you're not a professional sprinter and your goal is to burn fat, then don't think sprinting will get you there faster. You are much better off investing in a THR watch and walking at your fat burning zone. You are also much better off eating complex carbs like brown rice than simple one because it provides your body with a steady input of energy without spiking your insulin level, knowing that insulin is the hormone responsible for fat storage.