Here is the thing, forget the "meat" argument for a second - fine, take eggs, for example. Like meat, they are very calorie dense. But, you can't absorb all of those calories in a form where they must be burned off. You can absorb some of them of course. Remember that protein (and fat) has to be broken in to aminos, then carbohydrates, to sugars, and finally to glucose before it can be used for either energy or fat formation. So the process to get there is inefficient and a lot is used up on the way. Starches? They are nearly already there, so you will essentially absorb all of those calories. I can eat 4,000 calories a day of protein and not get fat. Half of that in starches has me gaining weight.