I'm curious to know how many of us (I raise my own hand here) apparently have genes which do know this.

My daughter seems to. Her mother and older sister are both stick figures (the middle sister takes a little more after her father, who was plumpish), and she tends not to eat all of any given meal and never has. (Though on Saturday she ate chocolate until she threw up, and thereby learnt an important lesson about gorging oneself on chocolate ... maybe.)

Ferriss also has a suggested plan for skinny guys who want to bulk up, FWIW.