As I was losing the bulk of my weight, I was always curious about where the physical fat went. Did my body eat it up? Did fat cells die and get flushed? Were they burned up in some process? This article helps explain it all. The tl:dr version is this: “When fat is lost, it is mostly exhaled as carbon dioxide (84%), with the remainder (16%) being excreted as water.” Wow. The processes within our bodies are extraordinary and complex.