When we exercise hard, we burn fat. But have you ever wondered where exactly the fat goes?

    Some doctors think that fat is changed into heat and given off in the air. Others think the body burns it. Some even joke that someone comes and takes it. That's why you always weigh less in the morning.

    Now a new study from Australia solves the mystery(迷). “The correct answer is that most of the fat is breathed (呼吸)out as CO2. It goes into the air.” says the study.

    Scientists followed the atoms (原子) in 10 kilograms of fat as they are lost. They found that 8.4 of those kilograms are breathed out as CO2 through the lungs (肺). The other weight, 1.6 kilograms,becomes water and leaves the body.

    “None of this is easy to understand because we can't see the CO2 we breathe out.” said the study's lead expert.

    Does that mean you can lose more weight by breathing more? It is not as easy as you think.

    Breathing more than the body's metabolic rate (新陈代谢速度) can make you uncomfortable. You may feel dizzy(眩晕的) and become unable to see, move or feel, according to the study.

    So how can people lose weight healthily? The key is to eat less and move more. You may have heard this many times. During a day, a 70kg person breathes out about 200g of CO2. So if the same person wants to lose weight, he or she can do some light exercise, for example, walking fast.This can help lose 240g of CO2.