I was reading an article today about junk food being addictive. Not new news, but this showed that rats given only junk food (high fat, salt and sugar) not only became obese, but their brains actually altered so that they no longer produced the hormones that tell the body it has eaten enough and it's time to stop. How scary is that?
And worse, the article implied that repeated exposure to junk food made changes to the brain that were not reversible without the whole cold turkey thing, if at all.
I'm not a McDonald's fan anyway, but that knowledge will make driving past a LOT easier now.
ETA: I forgot to say that when the junk food rats had their junk food taken away and were given only healthy food, they wouldn't eat it. Some starved themselves for weeks rather than eat the good stuff.