A paper recently came out with the conclusion that when it comes to body fat, it's calories that matter. I take issue with that conclusion on a few accounts, but first thing first:
You can read the intro ad abstract here.
You can access the entire paper here.
An Excess of HOW much?
The subjects were overfed by 1000 calories a day (40% more than weight stabilizing caloric needs), with varying levels of protein and fat, and the same level of carbohydrates.
Their conclusion that "calories alone account for the increase in fat" was based on the observation that "[b]ody fat increased similarly in all 3 protein diet groups and represented 50% to more than 90% of the excess stored calories."
We all know that insulin spikes in regards to carbohydrate consumption, but if you eat enough protein at a sitting, you can get insulin spikes, too. Drinking lots of protein in a shake after a workout will give you an insulin spike. Of course, if you're an athlete, that might be desirable.
I took a look at the diet laid out. Every single breakfast was carb based. Every. Single. One. Your insulin levels are naturally higher in the morning in response to higher levels of cortisol (an evolutionary thing that helps us be more alert upon waking). If you eat a bunch of carbs right then, your body is already primed to shove that junk away.
Low Protein = less weight increase?
At first glance "Hey, low protein means they didn't put on as much weight!" But wait! They have the same increase in body fat! That means they lost mass somewhere, and that is going to be in lean tissues (read: muscle).
PLUS! "In contrast, resting energy expenditure... and body protein... increased significantly with the normal and high protein diets." (Crazy data numbers removed.) So let's see. Even with a crap breakfast, these two groups saw a greater resting metabolic rate and more muscle.
This might be more extrapolation than most scientists would be comfortable with, but given this study and other articles I've read, I'd say it's pretty safe to conclude that high protein diets with increase your energy expenditure and help maintain lean tissue mass. And if you don't force yourself to read 40% more calories than you need (which, frankly would be hard to do if your carbs are kept to 20-30%) you're really setting yourself up for success.
All in All..
I would say that a diet 40% in excess and 41% in carbohydrates, regardless of protein levels, is not optimal. And I would venture to say it is STILL not about the raw calories. (Again, look at what each group ate for breakfast.) And even so, if you're going to eat "in excess", you will add and retain muscle mass in proportion to the levels of protein you consume.
I don't think this needs to be said, but... MOAR SQUATZ and MOAR STEAK! :)