In a recent paper in PLoS One, Lenoir, Serre, Cantin, and Ahmed make the startling discovery that sugar and artificial sweetener are both more addictive than cocaine.
In previous studies, it's been shown that animals will consistently choose cocaine over food. However, that worked used conventional feed for the animals in question -- in other words, healthy food. Lenoir et al did a head-to-head comparison between intravenous cocaine and the artificial sweetener saccharin, and found that over 90% of animals choose saccharin. They then repeated this test using the natural sugar sucrose. Once again, the sweetener won over cocaine.
This result -- that has not yet received any significant publicity -- suggests just why the abundance of high-fructose corn syrup and other sugars in our food products is so destructive. It may not be a simple matter of abundance that leads to obesity in developed nations, but instead a matter of exactly what we put in our foods. This could also help explain why obesity has not been as much of a problem in developed Europe, Korea, and Japan, but is a problem in other nations ascending to developed status.