If one eats slow the brain has time to "chat" with the stomach...hence you will feel full faster and eat less!
You need to eat till your satisfied not too much, it takes twenty minutes for your brain to send signals to your stomach that your full.
It is bad to eat fast because then you can't chew properly and you finish your food really fast which then instead leaves you craving for more!
When your stomach is full brain came to known after 15 minutes and if you east fast then imagine how much overeating you can do in this 15 minutes. So doctors always say: Chew the meal properly in order to eat less and you will automatically eat slow
Your mind and body take up to 20-30 min to fully be satisfied. When you hurry, your not getting the right nourishment and you can't tell whether you still hungry or full.