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Research suggests that years of eating the usual Western fare may affect the area of the brain that regulates metabolism. Specifically, it confuses the messaging system, so that you may not be able to accurately assess things like hunger, appetite and fullness. 
The good news is, there are ways to overcome it. For one, omega-3 fatty acids, such as those found in fish, may help regulate those changes. Adding fish, flax seed, nuts and soybeans to your diet is a good place to start. 
Taper your use of artificial sweeteners and start eating more fruits and vegetables to keep your blood sugars stable. Adopting a healthy diet high in vegetables, fruits, and whole grains and low in healthy carbohydrates, saturated fats, and sodium can retrain the brain. Exercise, adequate sleep, and stress management help cut cravings too.