The Mediterranean diet is often touted as a sort of anti-diet: a recipe for health and longevity that revolves around the region’s celebrated love of olive oil, vegetables, nuts, seafood and the occasional glass of red wine. 

But even this seemingly less dogmatic prescription is laced with complexity. First, the evidence is questionable: Much of the credit applied to the Mediterranean diet was fortified by a 2013 study run by PREDIMED, which has now been widely discredited, since approximately 20% of the participants were not randomly selected.

More importantly, it is hard to say what the Mediterranean diet actually refers to. Eating habits differ wildly between Tunisia, Israel and Albania, all of which number among the 22 countries that hug the sea. Greece, Italy and Spain are the c...