I'm trying to confirm the method by which the body physically loses weight during "long-term" weight loss. I'm specifying "long-term" here because obviously there are lots of ways to temporarily lose weight. Loss of water (jogging in the sun while wearing garbage bags to promote sweating?) can potentially lead to quick weight loss, but presumably the body just reclaims that water later. I'm referring to scenarios where a person, for instance, loses 100 pounds over a course of months via lifestyle changes like exercise and dieting. When this happens, how does the human body physically remove the weight?
It's long been my understanding that the answer is, effectively, "by breathing it out" (you breath in O2 and breath out CO2, with CO2 weighing more). This fact has always amused me (it's hard to imagine someone losing 100 pounds one breath at a time). I mentioned this "fact" to my wife recently and she looked at me very incredulously. I then realized two things: I had come to this conclusion myself but never actually verified it, and I wasn't sure how to explain the details enough to convince my very dubious wife.
I'm especially curious how much weight is actually lost (on average) per breath, and if there might be other physical processes which contribute to long-term weight loss. Obviously I'd be especially interested to find out that my expectation is completely wrong!