I used to be too skinny. When I started college, I was a shade over 6 feet tall and weighed a shade under 125 pounds. That has gradually ticked upward, until 25 years later, my BMI flirts at the upper edge of the recommended range.
I had started to enumerate the reasons why I think this is so, but it boils down to this: I eat too much, and I exercise too little. Why I do (or do not) these things is irrelevant.
So I checked this book out of the library. It's largely made up of motivational fluff, but it's peppered with a bit of science, some pseudo-science, and this very sound advice: eat what you want when you're hungry; slow down and mindfully enjoy what you eat; stop eating when you think you're full. The book includes a CD with a half-hour hypnotic induction session in which McKenna growls in your ears, urging you to visualize yourself thinner, happier, healthier. (Seriously, McKenna's voice is very, very deep, and at times it's like he's croaking. But it's also kind sexy).
I'll give it a couple weeks, and we'll see how it goes. If nothing else, I believe that mindful attention to what I'm doing is always a good thing.