Hello all.

In a successful body weight reduction; the loss of mainly fat tissues, its mass becomes energy used by the body, or is excreted as urine, as stools, as sweat ?  Where that lost mass goes / becomes ?  Any byproducts too ?

1 minute ago, Externet said:

Hello all.

In a successful body weight reduction; the loss of mainly fat tissues, its mass becomes energy used by the body, or is excreted as urine, as stools, as sweat ?  Where that lost mass goes / becomes ?  Any byproducts too ?

The fat, which provides energy to the body, does so by being oxidised to water and CO2, just like carbohydrates, but involving a different reaction of course. The CO2 is exhaled through the lungs and the water is excreted via the usual processes. 

Well, firstly about mass becoming energy. Remember E=MC²  ?  If there was any conversion of mass into energy (which I don't know) it would be absolutely tiny, and so can be ignored for practical purposes.

As far as the fat goes, exchemist is correct above. And bear in mind that body fat is about 20% water to start with (on average). 

 

Energy is obtained from stored fat by breaking down large molecules into smaller, simpler ones, until you have usable carbohydrates. The depleted fat cells shrink to fraction of their size, which accounts for the change in body shape. 

the bottom line is that most of it is breathed out as CO2 and water.