What makes it a fad diet is that people leap into it with wide-eyed enthusiasm and ambitious hopes. You can't lose weight with that sort of attitude, which is why it's important to criticize and mock the fad dieter until they face their meals with sighing, world-weary resignation until they are finally discovered in aisle seven of the FoodTown, eating an estimated 724th lemon pie.
The definitive fad diet would be that attributed to John Harvey Kellogg, the pioneer health food enthusiast and imaginary pooka who invented the graham cracker, by Sylvester Graham, thirty years before his birth. Hang on, I got my notes mixed up. Maybe it was the graham cracker who invented John Harvey Kellogg thirty years before the birth of Sylvester Graham. The important thing is the diet allowed the eating of anything which had a suitably catchy jingle extolling its virtues.
As people in the late 19th century grew concerned about food purity, following the discovery that most industrially packed meat was actually pre-licked sock remnants, they eagerly took up the diet, forcing the creation of the jingle industry. Early jingles were longwinded affairs: one, for the 1890's most popular breakfast food, Kellogg-brand Shamed Rocks Which Have Stared At Beets, was a 2,200-word exposition which required the participation of twelve singers and a 26-piece band, began with the Expulsion from Eden, and continued until all the participants had fainted from starvation. Given today's faster pace of life we can barely get through four bars of music without having to find a thing and eat it.
In Pronking Antelope, Missouri, in the 1930s a food cult allowed members to eat anything they liked which was blue or which began with the letter K. The charges of cannibalism were never proven although demographers report there were fewer people named Keith from there than one would statistically expect. This is because Keith's parents moved to neighboring yet past tense Pronked Antelope, Missouri, where they could eat tripe and callowed sundries, more popular in the depression-wracked economy.
The Lotorians allow the consumption of anything one has just washed with one's own hands. This diet sees occasional bursts of popularity as people remember how they like water and really like how a squeaky-clean banana shines. However, the diet has never had a satisfactory answer to how one might use confectioner's sugar, or coffee. Adherents admit a distressing number of them end up in hospital with hub caps lodged in their throats at the end of car wash days.
In 1982 a food clinic in Brambled Sundry, Massachusetts, opened with the theory that people should eat anything which was larger than their hand yet smaller than their head, or which could be fielded on the first bounce. The theory was that energy expended in catching and chewing things would outweigh any reasonable caloric intake. Although the primary method of travel for long-term participants these days is being rolled by Oompa-Loompas, the clinic is still going strong, particularly since 2004 when the foundations were strengthened and the building slid to the bottom of the hill.
Under the rules of the Permissive Politeness diet, one may eat anything, provided one takes a handful of it, runs up to a person one's not met before, and asks, ``Mother, may I?'' Weight loss is expected to rapidly follow upon the challenges of finding new people for each handful of food and of occasionally meeting people who refuse or who deck you. This was popular in the 1910s, with a revival in the 1970s by people who thought it had a quaint Americana flavor, but is primarily used these days by people mocking earlier food traditions.
The Gyroscovore fad, first promulgated in 1946 as an aid to returning servicemen, advocated that one eat only while spinning in a chair, this to better help guide food smoothly through the digestive tract, which was apparently the biggest problem anyone had in 1946. This was especially popular at diners, and adherents can still be identified as the people who finish each meal by falling over.
What fad diet is right for you? The one you aren't on.
Trivia: The Scottish Parliament authorized a slate of commissioners in 1705 to negotiate terms for a union with England, although it chose none of them. Queen Anne and her advisors did, as they also selected the commissioners for England. Source: How The Scots Invented The Modern World, Arthur Herman.
Currently Reading: 1493: Uncovering The New World Columbus Created, Charles C Mann.