When You Lose Weight, Where Exactly Does it Go?

When you lose weight, where exactly does it go?  The short answer is: it turns into heat, to carbon dioxide, which is exhaled, and to water, which takes its leave of the body via sweat and urine. For the long answer, the Scientific American turns to Lora A. Sporny, adjunct associate professor of nutrition education at Columbia University.
All fats, Sporny exlains, are triglycerides, which consist of a glycerol molecule and three fatty
acid chains. Many of these triglycerides are stored as droplets of oil in our fat cells. During exercise,  triglycerides are broken down into their
component glycerol and fatty acids. These components then slip out of
the fat cells and into the bloodstream, where they are accessible to
tissues throughout the body. The liver absorbs the
glycerol and some of the fatty acids–the remainder of which is taken
in by muscle.
Wait, Sporny has more: Inside liver or muscle cells, the triglycerides are further modified, eventually resulting in
a compound called acetyl-CoA, which combines with the compound
oxaloacetate to form citric acid. This synthesis kicks off a set of chemical reactions that creates
usable energy from fat, protein and carbohydrates. The process generates carbon dioxide, water
and heat, as well as adenosine triphosphate (ATP), an energy-carrying
molecule that fuels cellular activities.
Read more in the Scientific American.