Body weight gain/loss is also governed by mass in versus mass out. So make an effort to inhale less than you exhale, drink less water than you expel via urination or sweat, and poop more than you eat. Any of those are guaranteed to work if you could sustain them, but you can't.

Which is nicely analogous to telling someone to focus on calories in versus calories out.

You lose mass by exhalation of CO2, not defecation. Since you inhale O2 and exhale CO2, you don't need to inhale more than you exhale (a mathematical impossibility anyway, of course) to lose weight.

Don't forget donating more organs than you receive transplants for.

Not all calories are absorbed. Also, I think it's safe to say that minerals and vitamins can contribute to structural/weight changes. Even water can.

Water can certainly affect weight, but only temporarily. You will not get fat drinking water.

Calories in-calories out declare the upper bound. No matter what vitamins you take, you can't make body produce more energy that it takes in, or else something in thermodynamics is seriously broken.

True, but useless. If the human body is extra efficient, it should have about 20% efficiency at converting energy. This means your upper bound rule tells you that if a male adult eats 400cal/day he'll lose weight. Duh! He'll lose weight at 1800cal/day; the 400cal mark is useless.

Thank you for putting into words what I was trying to think of. Different bodies operate at different metabolic/thermodynamic efficiencies depending on level and type of exercise and nutritional intake. (including non calorie nutrients like vitamins, minerals, flavanoids, etc.)