Here is the crux of things in my opinion. Anyone saying that building a better body and better health is solely about calories is very misguided. Obviously a calorie deficit comprising nothing but gum drops and jujubes isn't going to promote leanness and health as well as a diet comprising lean meats, abundant veggies and fruits, a balance of saturated, mono and polyunsaturated fats, etc.

At the end of the day though, I think you'd be hard pressed to show me sufficient peer-reviewed academic research that shows people losing weight in a calorie surplus or gaining weight in a calorie deficit, assuming we're talking about tissue weight and non-diseased people. But who cares about that since we're not here solely for weight loss. People, knowingly or not, are more interested in health and body composition.

And this latter focus requires calorie control AND nutrient control. One without the other is a pointless proposition. Anyone who's arguing that there aren't nutrient needs that need to be accounted for independently of calorie intake is sorely mistaken.

The people claiming that "all calories aren't the same" aren't grasping the specifics. A calorie is a calorie is a calorie... just as a meter is a meter. A calorie is merely a unit of measurement. You're confusing nutrients with calories... they aren't interchangeable. Nutrients provide our bodies energy that, for the time being, we quantify with an outdated metric known as the atwater system and calories. Yes, nutrients are not created equal in the "body's eye" which should be obvious to anyone. But that's not the same as saying, "all calories are not equal."

When you delve into the research pertaining to nutrient manipulation, if there are any clear trends, it's that there is no One Way that's right for everyone. People who espouse high carb diets to everyone are misguided just as people who espouse low carb diets to everyone are misguided. Individually tailoring a diet to the individual in question is a must if lasting change is going to be realized.

We have data out there supporting the idea that low carbohydrate approaches are better for some while higher carbohydrate approaches are better for others, further exemplifying why any blanket recommendations are sort of silly. Anyone who works with a wide array of folks in the fat loss setting can vouch that a myriad of diets work depending on the person and the situation. I can say this... in my experience, lower carb approaches tend to work best for my obese clients and by and large, moderate carb approaches tend to work best for my leaner clients. This most likely has something to do with insulin resistance/sensitivity issues which has already been mentioned in this thread.

When we get really lean, a that moderate carb approach tends to best be delivered within a cyclic approach. Put differently, I'll install punctuated periods of high carb intake at specific times of the week. Other periods of time will be on the lowish end of things.

And if you're truly trying to show that there is some sort of metabolic advantage for anyone eating low carb, you need to wait for sufficient research to be conducted comparing low vs. moderate or high carb approaches THAT MATCH protein and calories. The research simply isn't there yet though. James Krieger, an author and published researcher whom I highly respect and communicate with, put it perfectly when he said:

1. The proposed metabolic advantage (MA) for low carb diets is a hypothesis, not a fact
2. There is inadequate data to support the MA hypothesis
3. There is inadequate data to reject the MA hypothesis
4. The MA hypothesis does not trump the concept of energy balance. It postulates inefficiencies in energy metabolism, which would translate to an increase in measured energy expenditure (due to heat loss) in a living organism. Thus, if the MA was true, "calories out" would increase for a given "calories in".
5. A definitive study examining 24-hour energy expenditure (using room calorimetry), comparing a ketogenic diet to a traditional diet (with matched protein intake) for subjects in an energy deficit, has not been performed. This is the only study that will adequately test the MA hypothesis in humans
6. Weight loss still requires an energy deficit. If a MA exists, it still cannot make up for an energy surplus or energy balance. To assert otherwise is to assert that energy can be created or destroyed out of thin air, or that human tissue can be created in the absence of any energy input.

Mind you, his published paper on MA actually supports the MA hypothesis.

And what about insulin? Yea, it's true that having elevated insulin levels blocks fat oxidation and lipolysis on a meal by meal basis. But what happens if, say, you eat one huge meal and spike insulin to the moon, store fat, shut off lipolysis, etc. and then don't eat again for the rest of the day?

If that one meal was only 1,000 calories and you need 2,500 a day to cover your total daily energy expenditure, why exactly is the body just going to hang on to those calories when it needs them to survive?

And this doesn't even begin to factor in things like rate of digestion... eating even a high-carb diet does not necessarily imply chronically elevated insulin. And low carb zealots tend to look at things in a vacuum... insulin promotes fat storage, carbs spike insulin, therefore carbs make us fat. They leave out, as already mentioned, the myriad factors that also play a role in fat metabolism such as acylation stimulation protein, catecholamines, HSL, etc.

As I noted above, in the game of weight loss it is about thermodynamics before anything else. In the game of body composition and health, it's much more complex however.

For anyone interested in learning more about insulin and its relation to lipogenesis, I can't recommend Jame Krieger's series on it which you can find here:

http://weightology.net/weightologyweekly/?page_id=319

That's part 1 and you can continue on to the other parts from it.

Hopefully this post helps clear up some of the mysticism.