Thanks to the ingenuity of the human body, breathing out can help people to lose weight.

It’s because more than 80% of body fat leaves the body through exhaling via the lungs, after being broken down into carbon dioxide and water.

The research is great news for anyone likely to reach for multiple helpings – it is Christmas a second helping over the coming weeks. It’s even been published in the Christmas edition of the British Medical Journal.

A table set for Christmas
Breathing in after a big dinner might help the waist band, but breathing out is really key (Scott Brenner/Flickr)

As they would say in a 1990s/2000s’ L’Oreal advert, “here’s the science bit, concentrate.”

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.

Scientists at the University of New South Wales in Australia found that when 22lb (10kg) of fat is fully oxidised, 18.5lb (8.4kg) leave the body through the lungs as carbon dioxide (CO2). The remaining 3.5lb (1.6kg) becomes water.

A calculator
We’re just working out how long you need to exhale for (Paul Barker/PA)

It wouldn’t be particularly easy to achieve. The oxygen required for this process weighs nearly three times more than the fat being “lost”, so to completely oxidise 22lb (10kg) of human fat, 64lb (29kg) of oxygen must be inhaled, producing 62b (28kg) of CO2 and 24lb (11kg) of water.

The scientists, Ruben Meerman and Andrew Brown, said: “These results show that the lungs are the primary excretory organ for weight loss. The water formed may be excreted in the urine, faeces, sweat, breath, tears or other bodily fluids and is readily replenished.

“The exhaled carbon can only be replaced by eating food or consuming beverages such as milk, fruit juices or sugar-sweetened drinks.”

An obese woman picture sat down from the bottom up to her shoulders,, wearing jeans and a top
(Anthony Devlin/PA)

At rest, a person who weighs 11 stone (70kg) exhales around 200ml of CO2 by taking 12 breaths a minute.

In other words, 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.

Running machines
Exercise is still going to be key to weight loss (Tim Goode/PA)

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.

Essentially though, the researchers say the old adage rings true – “eat less and move more”.