Hara hachi bu is a Japanese phrase which translates to "eat until you are eighty percent full".
I think I discovered something that may help you learn how to do this.
"Kaye's Lunch" is what we call the type of lunch where we clear out the fridge, finish the left-overs and small nibbles of this and that. Since the flavours and textures do not always mix well, I wanted plates with divided sections. I lucked out and found some at a yard sale. Interestingly enough, these were made in Japan.
While enjoying our lunch, I noticed that for whatever reason, it seemed to slow down the speed of eating. It takes about twenty minutes for receptors in your brain to receive satiety signals. These signals, if you stop to listen to them, inform you that you are full - maybe even eighty percent full!
So, if you're trying to slow down and consume less, try the divided plate trick. While you're at it, you may also wish to use some chopsticks.
Will you please let me know how this works for you?