One reason that people leap from longevity to diet is a mental quirk known as the “you are what you eat” fallacy. Psychologists have found that people assume that the properties of food are transferred to those who eat it. In some parts of Asia, for example, tiger penises are eaten to increase men’s virility.
But it’s not specific to Asia. American college students show a similar superstition.
In one study, students learned about the cultural practices of two tribes. One was said to eat wild boars, whereas the other ate turtles. When the students were asked to describe the members of each tribe, they said the boar eaters were bearded and aggressive, and the turtle eaters were good swimmers with long lifespans.
The leap from healthy lives to healthy-seeming foods might just be the same error.
Medical evidence suggests that differences in lifespans across countries are better explained by social conditions than diet. Researchers have found that among economically developed countries, income inequality is a major predictor of longevity.
In fact, the most equal nations are Japan, Sweden, and Norway, which also have the longest life spans. Not far behind are Mediterranean nations including Spain, Greece, and Italy.
It’s no coincidence that all these highly equal countries have inspired fad diets.