Did you know that when you lose weight most of it is exhaled out through your lungs? If you follow the atoms in 10 kilograms of fat, as they are 'lost', 8.4 of those kilograms are breathed out as carbon dioxide.
The remaining fat becomes water, which may be excreted in urine, sweat, faeces, tears, breath and other bodily fluids, reports a study from UNSW School of Biotechnology and Biomolecular Science in Australia.
There is surprising ignorance and confusion about the metabolic process of weight loss says Professor Andrew Brown, head of the UNSW School.
The most common misconception among doctors, dieticians and personal trainers is that the missing mass has been converted into energy or heat.
"The general misconception is that fat is lost as heat through exercises. Around 50 percent of the 150 doctors, dieticians and physical instructors who were surveyed thought the fat was converted to energy or heat," the study's lead author and a physicist, Ruben Meerman.
Some of the people surveyed thought the metabolites of fat were excreted in faeces or converted to muscle.
"We suspect this misconception is caused by the energy in/energy out mantra surrounding weight loss. The misconceptions reveal surprising unfamiliarity about basic aspects of how the human body works," says the lead author.
The study clarifies that the metabolic process of losing 10 kilograms of fat requires 29 kilograms of oxygen to be inhaled and produces 28 kilograms of carbon dioxide and 11 kilograms of water.
Mr Meerman became interested in the biochemistry of weight loss through personal experience.
"I lost 15 kilograms in 2013 and simply wanted to know where those kilograms were going. After a self-directed, crash course in biochemistry, I stumbled onto this amazing result. With a worldwide obesity crisis occurring, we should all know the answer to the simple question. The fact that almost nobody could answer it took me by surprise," he said.
"Ruben's novel approach to the biochemistry of weight loss was to trace every atom in the fat being lost and, as far as I am aware, his results are completely new to the field," Andrew Brown noted.
One of the most frequently asked questions the authors have encountered is whether simply breathing more can reduce body fat. The answer is no. Breathing more by a person's metabolic rate leads to hyperventilation, which can cause dizziness, palpitations and unconsciousness.
The second most frequently asked question is whether weight loss can cause global warming.
This reveals troubling misconceptions about global warming. The phenomenon is caused by unlocking the ancient carbon atoms trapped underground in fossilised organisms. But, the carbon atoms human beings exhale are coming back to the atmosphere after just a few years trapped in food that was made by a plant.
Mr.Meerman recommends that these basic concepts be included in secondary school curricula and university biochemistry courses to make common people and health professionals aware about weight loss.