Grist.org has a fascinating article talking about how scientists claim junk food is as addictive as heroin.

http://www.grist.org/article/scientists-claim-junk-food-is-as-addictive-as-heroin

To pull a line from David Kessler's, The End of Overeating, get a bowl of m&m's and put it in front of you.  For the entire day try not to grab one m&m from the bowl.  If you notice, you will probably be preoccupied by wanting the m&m's.  Is something fishy going on here..?