 People have chewed coca leaves for at least 8,000 years as a mild stimulant without any evidence of addiction. But when certain components are isolated and concentrated into cocaine, we've got a problem. The same may be true of sugar. People don't tend to binge on bananas. It's perhaps the reason we're more likely to supersize soda than sweet potatoes, while we're less likely to overeat this kind of corn compared to that kind of corn. The overconsumption of sugar-sweetened diets has often been compared to drug addiction, though this parallel was based until very recently, more on anecdotal evidence than on solid scientific grounds. But now we have PET scans, imaging technology that can measure brain activity. It all started with this publication showing decreased dopamine sensitivity in obese individuals, and the heavier they were, the less responsive they appeared to become. We see the same thing in cocaine addicts and alcoholics. This would suggest that a reduction in dopamine receptors is associated with addictive behavior, irrespective of whether it's due to food or to addictive drugs as seen in substance abusers. Dopamine is considered the neurotransmitter primarily involved in the pleasure and reward center of our brain, helping to motivate our dry for things like food, water, and sex, all necessary for the perpetuation of our species. It was healthy and adaptive for our primate brains to drive us to eat that banana when there wasn't much food around, but now that fruit is in loop form. This adaptation has become a dangerous liability. The original Coca-Cola formulation actually included coca leaf, but now perhaps its sugar content may be the addictive stand-in.