a personal experience,, when I decided to go very low carb, I sat on the couch the first weekend due to my body unable to supply sufficient energy from fat. My point is adaptation is often overlooked. Carbs, especially cooked carbs are very addictive. Most will have an extremely hard time transitioning off them onto fats for fuel. And then most likely will give more credence towards theories such as metabolic typing etc. Not saying there isn't such a thing, but it takes a bit of dedication to experimentation to find out for one's self.