If fat and sugar are bad for you, why have we evolved liking them so much?
(Lansing State Journal, August 30, 1995)

Excess fats and sugars in one's diet can cause obesity, heart disease, diabetes and other health problems.  The key word here is "excess".  A certain amount of fat and sugar is necessary for us to be healthy.  The problem is that fat and sugar are so abundant that it's easy to eat more than we need.  During most of man's existence, however, this was not the case.  In fact, just the opposite was true.

Fats and sugars were hard to come by.  People who had a taste for fats and sugars were probably more likely to take advantage of foods with fats and sugars in them, when they had the chance, than people who didn't. In other words, these people would take in more of these necessary but hard to find nutrients and therefore would be healthier and more likely to survive extreme conditions.

Thus, people who had a desire for fats and sugars were "naturally selected" to survive over those who didn't.

Even though this trait is more of a disadvantage today, most of the health problems it causes aren't seen until after people have reached an age where they have reproduced.  Therefore, the trait isn't "naturally selected" out and still persists.

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