I hate the genetics argument.  Fat is not genetic.  A hundred years ago, weighing 300 pounds was enough to land someone in the freak show at the circus.  Thirty years ago, being fat was so uncommon that there was only one or two butterballs in any given school district (and they were teased mercilessly, as they should be).  Only microscopic organisms can make enormous changes to their genomes within one or two generations.  Even though fats are a plague upon society, that doesn't make them viruses.  Maybe the same IQ though...