Question: When humans lose weight where does it go? I read that most of it leaves our body as carbon dioxide (CO2) through respiration. Is this true? How does this work?

Dear awesomekid,

Thats right. So when you lose fat, your fat cells shrink and the fat molecules are broken down by the body to use as energy. The fats are broken down into two parts called glycerol and fatty acids. These molecules are used by your body, liver and muscles etc.

These two parts are broken down further through a series fo chemical reactions (you may have heard of the TCA or CREB cycle?) to produce heat, the essential form of energy that your body needs to live. The waste products from this process are water and CO2. The body gets rid of excess water in urine and the CO2 through our lungs. 🙂