Why is overrating become addictive after a while, especially when it comes to unhealthy foods?

Over-eating?: Do you mean over-eating being addictive? It can become "addictive" to some people because of the content of unhealthy foods. Just like people can be addicted to caffeine, some studies have shown that people can get addicted to the simple sugars or fats found in most unhealthy foods. It also may be a stress relief behavior, eating causing endorphins ("happy/relaxing" molecule) to be released.

Mind: Anything that u repetitively imagine in ur mind can become addictive. Food, alcohol, merchandise (shopping addiction, ) gambling. That's why meditation and support groups are often helpful. Nothing done compulsively brings you honest enjoyment. It can make u depressed by taking ur attention away from the good things in life, like generosity, love and creativity. When u crave food, serve it 2 others.

Depends on food: Foods with refined sugars (cookies, soda) and easy to absorb sugars (potato chips, fries) cause a high spike in blood sugar. This is a rush. A spike in sugar causes a spike in insulin, which brings down the sugar. Because of the high initial peak, there's an overcorrection and now you have a low sugar = hunger. So junk food is like crack. An initial rush followed by a down and a search for more.