It actually takes your stomach quite a while to tell the brain "Hey I'm full!" I've heard you should try to make your meals stretch out to take 15 minutes to eat at least. Obviously a granola bar will not take that long- but a full meal should
I used to watch the clock, purposely put down my fork, take a drink, and so on, just to make sure my meal lasted long enough- now it comes more natural
I prefer to eat slow and my husband complains about it lol- but then again he's the kind who shovels his food so fast that all of a sudden he'll stop and be like OMG I'm STUFFED.