Humans have a type of fat in our blood called triglyceride, which consist of three kinds of atoms - carbon, hydrogen and oxygen.
Shedding unwanted fat requires unlocking the atoms in triglyceride molecules through a process known as oxidation.
A report from the University of New South Wales says a person who weighs 11 stone (70kg) exhales around 200ml of CO2 by taking 12 breaths a minute.
So by breathing out 17,280 times a day they will lose at least 200g of carbon, with around a third of that weight loss achieved during eight hours of sleep.
But to keep the weight off requires putting less back in through eating than is exhaled by breathing - which might be tricky come that second turkey sandwich on Boxing Day.
Going for a run for an hour would help remove an additional 40g of carbon from the body, the researchers say, raising the total loss by around 20%, to 240g.
But that can be wiped out by a single 100g muffin, which represents around 20% of an average person’s total daily energy requirement.
Report authors Ruben Meerman and Andrew Brown said: “Physical activity as a weight loss strategy is easily foiled by relatively small quantities of excess food.
“Our calculations show that the lungs are the primary excretory organ for fat. Losing weight requires unlocking the carbon stored in fat cells, thus reinforcing that often heard refrain of ‘eat less, move more’.”