Well, maybe the "F" stands for "fancy", so it's "Fancy American Diet" :)
Thank you, Debbie and Patrick !
A fad is any form of behaviour that develops among a large population and is collectively followed enthusiastically for a period of time, generally as a result of the behavior being perceived as popular by one's peers or being deemed "cool" by social media. A fad is said to "catch on" when the number of people adopting it begins to increase rapidly. The behavior will normally fade quickly once the perception of novelty is gone.
The specific nature of the behavior associated with a fad can be of any type including language usage, apparel, financial investment, and even food. Apart from general novelty, fads may be driven by mass media programming, emotional excitement, peer pressure, or the desire of "being hip".Fads may also be set by popular celebrities.
Though the term trend may be used interchangeably with fad, a fad is generally considered a quick and short behavior whereas a trend is considered to be a behavior that evolves into a relatively permanent change.