When you lose weight where does it go?

Where Weight Loss Goes

Weight loss does not mainly leave the body through sweat, urine, or exercise-related muscle changes. As the body loses fat, much of its mass leaves through breathing: oxygen is inhaled, and carbon-containing carbon dioxide is exhaled.

The subtitles state that about 84% of lost fat is breathed out as carbon dioxide; most of the remainder is associated with water. Each breath removes only a tiny amount of mass, so breathing faster is not a useful way to lose weight.

Source

No researchers are named. The video says the question came from the Elements of Truth trivia game.