Normal Fat
Normal fat is the subcutaneous (under the skin) fat (SC fat) that our uses to store fat (energy). SC fat cells are able to respond to energy regulatory hormones (such as insulin, adrenalin etc) because these cells have receptors that can bind to these hormone molecules. After eating a meal, the food is absorbed into the blood causing a rise in energy (fat and sugar etc). This rise in energy in turn causes changes in hormones. The hormones changes then push the extra energy that you just ate into the SC fat to be stored. Between meals, the lowering of your blood energy levels due to continuous energy consumption such as heart beating triggers your SC fat to release energy into the blood. This flow of energy back and forth between blood and SC fat is regulated by your hormones and reaches a balance under normal circumstances.
Many of citizens of developed nations, esp. Americans, consume a lot more energy than their body needs. They fill up their SC fat area at a very young age, teens or even below teens. Their SC fat area is full and there is no more space to store any more energy. But these people didn’t stop eating. The extra energy starts accumulating in their blood, causing a rise in their sugar and fat levels. The high level fat then starts diffusing out of blood vessel walls into other areas where the fat level is lower. This is a physical diffusion process (just like water will flow high level to low level). These fats accumulate in the visceral fat areas (lipophilic, or fats attract fats).
Abnormal Fat
Belly fat represents the abnormal fat. These are the fatty tissues found around the internal organs, hence the name visceral fat. These fatty tissues are meant to protect the organs (they form a capsule around your stomach, or liver or muscle). These fatty tissues are not designed to store energy. These fatty tissues don’t have (or very few) receptors to respond to the energy regulatory hormones. The usual diets such as Weight Watchers, South Beach diets or regular medical diets including an appetite suppressant, do not lose your belly fat. This is because these diets make you eat less which in turn triggers hormones to release energy from the SC fat, not the abnormal visceral fat.