A few weeks ago I asked a National Academy scientist, whose research focuses on obesity issues, if sugar is addictive. He said that, according to the definition of addiction, the answer is no. His wife turned to me and said that she thinks it is. I did a little more research and found this in Wikipedia:
“Any concept of sugar addiction is complicated by a lack of consensus on the actual definition of addiction.” Further down the article sites a study by Takashi Yamamota, and reports “Sugar and the taste of sweet stimulate the brain by activating beta endorphin receptor sites. These are the same chemicals activated by heroin and morphine.” 
The article goes on to site sugar studies with lab rats, which concluded that, rather than becoming addicted the rats became “sugar-dependent.”
I think the quality and kind of sugar makes a big difference in how much sugar we eat and am curious — How many of you have eaten more than one apple at a time? How many stop at one cookie? If you eat an apple do you find yourself craving more apples? If you have one cookie, regardless of actually eating more, do you want more?