There is an enormous difference here. Even fast food chains themselves accept that their product should not be eaten all day everyday. Supermarkets have taken on board healthy messages about people's five a day or low fat brands. They've built these messages into their wider marketing strategy. Diet ads, by contrast, do claim to be a panacea that will instantly make you sexy, healthy, popular and, apparently successful. They are 21st century snake oil merchants and should simply be run out of town.