Moderation is psychologically more difficult to adhere to than explicit prohibition. Most drivers routinely exceed the speed limit, but they rarely jump red lig

Moderation is psychologically more difficult to adhere to than explicit prohibition. Most drivers routinely exceed the speed limit, but they rarely jump red lights. Religious laws have lots of "thou shalt not", but rarely any "thou shalt only in moderation". The laws of kashrut are incredibly inconvenient, but they're remarkably easy to follow in practice because they're absolute - either a food is kosher or treif, with no middle ground. You don't have to exercise judgement or restraint, you just have to blindly obey a set of well-documented rules. Fad diets like paleo are ostensibly irrational, but they're a good fit for human psychology. Counting calories is a minefield - it's too easy to slip up, too easy to deceive yourself about the size of a portion, too easy to nibble at something while you're cooking and forget to count it. A diet that says "don't eat grains" might be theoretically sub-optimal, but it's easy to stick to and much more resistant to self-deception. Exclusion diets also front-load the burden of self control. If you don't buy any cookies, you have to get into your car and drive to the store if you get a craving for them. If you've got a jar full of cookies, you're relying on pure self control to eat only one rather than scarfing the whole lot. They're always sitting there on the counter, tempting you to break your diet.