The most common misconception among doctors, dieticians and personal trainers is that the missing mass has been converted into energy or heat. "There is surprising ignorance and confusion about the metabolic process of weight loss," says Professor Andrew Brown, head of the UNSW School of Biotechnology and Biomolecular Sciences. "The correct answer is that most of the mass is breathed out as carbon dioxide. It goes into thin air," says the study's lead author, Ruben Meerman, a physicist and Australian TV science presenter. ------------------- The second most frequently asked question is whether weight loss can cause global warming.