By Carmen Chai
TORONTO – You’re losing weight when you’re biking to work, carrying groceries to your trunk and…while you’re watching TV on the couch.
That’s because you’re breathing – and the more you breathe, the more fat you exhale, Australian researchers suggest. In the annual Christmas edition of the BMJ, the scientists explain where fat goes when we lose weight.
“Considering the soaring overweight and obesity rates and strong interest in this topic, there is surprising ignorance and confusion about the metabolic process of weight loss among the general public and health professionals alike. We encountered widespread misconceptions about how humans lose weight among general practitioners, dietitians and personal trainers,” the University of New South Wales researchers wrote.
“Most people believed that fat is converted to energy or heat, which violates the law of conservation of mass. We suspect this misconception is caused by the ‘energy in/energy out’ mantra…,” they said.
(Others thought that the weight was excreted or turned into muscle.)
So where do the pounds go as we’re dropping a dress size? The scientists – Andrew Brown and Ruben Merriman – say they disappear into thin air as we breathe.
When about 10 kilograms of fat – or roughly 22 pounds – is broken down in oxidation, 18.5 pounds leaves the body as exhaled carbon dioxide, while the rest is breathed out as water vapor, Today explained.
About 16 per cent of weight released from the body is water weight – sweat, tears and urine, for example.
“Our calculations show that the lungs are the primary excretory organ for fat,” the scientists wrote.
It doesn’t mean you can breathe your way into swimming suit season.
But exercise is a good start: An average 155-pound person exhales about 200 mililitres of carbon dioxide in 12 breaths per minute. In a day spent asleep, at rest and performing light activities we exhale 203 grams of carbon from the body. For perspective, about 500 grams of sucrose contains 210 grams of carbon.
If instead of an hour in front of the TV, you spend an hour on the treadmill, you’ll get rid of an additional 39 grams of carbon for a total of 240 grams.
“For comparison, a single 100 gram muffin represents about 20 per cent of an average person’s total daily energy requirement,” the researchers conceded.
“Physical activity as a weight-loss strategy is easily foiled by relatively small quantities of excess food,” the researchers said.