Just before Fast Food Nation came out, the Guardian ran an extract about food flavouring that includes a visit to the place where the flavouring for McDonalds food is made.
http://www.mcspotlight.org/media/press/mcds/theguardian0704011.html"Grainger had brought a dozen small glass bottles from the lab. As he opened each bottle, I dipped a fragrance-testing filter into it. The filters were long, white strips of paper designed to absorb aroma chemicals without producing off-notes. Before placing the strips of paper before my nose, I closed my eyes. Then I inhaled deeply, and one food after another was conjured from the glass bottles. I smelled fresh cherries, black olives, saut*ed onions and shrimp. Grainger's most remarkable creation took me by surprise. After closing my eyes, I suddenly smelled a grilled hamburger. It smelled like someone else in the room was flipping burgers on a hot grill. But when I opened my eyes, there was just a narrow strip of white paper and a smiling flavourist."
I haven't eaten at McDonalds, Burger King et al since. If the smell and the flavour of the food you experience is an additive out of a bottle, what does the stuff you are eating smell and taste like without it?