[montecarl]

Is your statement true? Why should it be a forgone conclusion that our bodies are able to convert all macronutrients into energy with 100% efficiency? If you maintain a stable weight for 1 year does this mean you managed to perfectly balance caloric intake with caloric expenditure? That when you ate that extra cookie or drank an extra soda that you needed those calories to offset some energy expenditure? That seems hard to believe.

One interesting question that I do not know the answer to is the kinetics of metabolism for different macronutrients. How quickly can our bodies metabolize fat, protein, and carbohydrates? Is it possible that our bodies convert carbohydrates into energy very quickly, thus leading to an excess of energy that gets stored as fat? While other nutrients get digested much more slowly and only used if needed?

The basic question is do all ingested calories get used? Does the body have a mechanism for maintaining a certain "ideal" weight that can function across a range of caloric intakes?

[jacques_chester]

The calorie labels you see on food are adjusted to account for average digestive and absorptive effects for the mix of macronutrients in that food.

Calories in - calories out doesn't mean "Calories on food label minus readout on the treadmill". It refers to the actual energy balance. Under no reliably observed circumstances has human biology been shown to violate the conservation of energy and matter.

The point of repeating "a calorie is a calorie" is to reconcile people to the inescapable fact that a caloric deficit, no matter how imposed, is the necessary and sufficient cause of lowered long term average body mass.

The problem is that some folk like to embrace Nirvana Fallacy as some kind of debating trump card. "You can't calculate future weight down to 1 gram resolution 6 months from now, therefore your premises are totally wrong!"

Well I can't predict the temperature in my bedroom exactly 6 months from now either. But I have a pretty good idea of what season it will be.

[eru]

One trivial stabilizing mechanism is that more bodymass needs more power even at rest. So if you were perfectly balanced now with your current diet and current weight, and added the same snack every day, the only change would be a slight one time gain in weight.

Different foods make you eat more or less, by eg filling you up faster or keeper you satiated (and satisfied) for shorter or longer. So if you want to test your hypothesis, you'd have to carefully control for these effects, in order to rule out that caloric input is king. (I.e. my null hypothesis here is that caloric input is what counts in the end, but different foods have an influence on how many calories you actually consume.)

Anyway, the caloric surplus was just a simple example. Perhaps a clearer example would have been `trying to gain weight through fasting'.