Much of the total supply of water the human body NEEDS is supplied by the metabolism of food for energy. Carbon dioxide is NOT the only metabolic product our bodies generate, every exhaled breath also carries 100% relative humidity of water vapor. Oxygen could not be exchanged in your lungs without this highly humid interface.
Small horses have lived for YEARS on the tops of mesas with no liquid water available, as the digestive processes of horses (and many other herbivores) can extract the water even from dead-grass forage, by metabolizing the energy contained in those collections of normally indigestible carbohydrates.
Little secret: you do not lose weight by sweating it off, you lose body mass and fat layers by metabolizing the tissues of your body, and these pass off through your breath. Breathing in oxygen accelerates the weight loss equation.
Interesting.
what do you mean by metabolizing your body tissue ?