I don't believe that fast food IS so tasty! This question assumes that we are born with natural taste preferences and that fast food naturally fits these. I think that we learn our taste preferences through exposure to different foods (we like what we are familiar with), through watching others (we like what others eat) and through association (we like whichever foods we associate with nice things such as smiling parents, good times or feeling happy). To some, fast foods may be tasty because they have learned to like high salt, high fat or high sugar foods. But to others who have not learned this fast foods taste plastic, artificial, salty, oily, greasy or just plain 'grim'. So the question makes many assumptions that I just don't think are justified!