How to convince my brain to stop overeating???

The obvious fact is that all my life I've eaten too much. But why?
Throughout our evolutionary history, food has been scarce, so in order to ensure survival, humans have been conditioned to eat as much as they can whenever food is available.
Unfortunately, when food is abundant and rich in calories, as it is today, the results can be ugly.

~ SO that is an ad for a new product, but it really describes how I feel a lot.
How do I convince my mind I am full before I am SO full???
Got any ideas...