# When you lose weight, what do you lose and where does it go? **URL:** \ **Category:** Factual Questions\ **Created:** [August 6, 2006, 6:23am UTC](https://boards.straightdope.com/t/when-you-lose-weight-what-do-you-lose-and-where-does-it-go/367535 "2006-08-06T06:23:03Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![Muad\_Dib](https://avatars.discourse-cdn.com/v4/letter/m/35a633/32.png) [@Muad\_Dib](https://boards.straightdope.com/u/Muad_Dib)\ **Post date:** [August 6, 2006, 6:23am UTC](https://boards.straightdope.com/t/when-you-lose-weight-what-do-you-lose-and-where-does-it-go/367535/1 "2006-08-06T06:23:03Z")
What happens to the “burned” fat? What does it turn into and how is it excreted? ---
**Author:** ![Airman\_Doors\_USAF](https://avatars.discourse-cdn.com/v4/letter/a/e36b37/32.png) [@Airman\_Doors\_USAF](https://boards.straightdope.com/u/Airman_Doors_USAF)\ **Post date:** [August 6, 2006, 6:35am UTC](https://boards.straightdope.com/t/when-you-lose-weight-what-do-you-lose-and-where-does-it-go/367535/2 "2006-08-06T06:35:36Z")
It turns into “energy” and it is excreted in the form of urine and feces. Just like any other food. ---
**Author:** ![Civil\_Guy](https://avatars.discourse-cdn.com/v4/letter/c/d78d45/32.png) [@Civil\_Guy](https://boards.straightdope.com/u/Civil_Guy)\ **Post date:** [August 6, 2006, 6:42am UTC](https://boards.straightdope.com/t/when-you-lose-weight-what-do-you-lose-and-where-does-it-go/367535/3 "2006-08-06T06:42:00Z")
My general understanding: some good part of it turns into carbon dioxide, expelled by the lungs. Some part of it turns into other biochemicals, excreted through other ways, including shit. This is pretty complicated: what actually gets excreted, a lot, is bacteria that grew fat and happy off of the various biochemicals that got into the intestines. The process of “burning” the fat is a chemical process that in various ways probably resulted in heat output - the heat was expelled by the skin and sweat, mostly, with some going out with urine and heated exhalation. Water comes and water goes - it’s possible (as far as I know) that some of the fat got broken down into carbon dioxide and water - and the extra water was put into urine, sweat, and moist air from the lungs. If it’s not obvious by this point, let me announce that I am not a medic, a doctor, nor a biochemist. Hopefully one will be along soon. Because it’s quite complicated, the subject has been the subject of many discussions. ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [August 6, 2006, 7:15am UTC](https://boards.straightdope.com/t/when-you-lose-weight-what-do-you-lose-and-where-does-it-go/367535/4 "2006-08-06T07:15:17Z")
After being metabolized a surprisingly large portion of the burned weight of fat is released as carbon dioxide through breathing. ---
**Author:** ![Renee](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/renee/32/287_2.png) [@Renee](https://boards.straightdope.com/u/Renee)\ **Post date:** [August 6, 2006, 7:17am UTC](https://boards.straightdope.com/t/when-you-lose-weight-what-do-you-lose-and-where-does-it-go/367535/5 "2006-08-06T07:17:17Z")
If I may add to this question: I have always heard that once you gain fat cells, you can’t lose them, only deflate them. Any truth? Along these same lines, I have heard that if you get liposuction and then gain weight, the weight will accumulate in your remaining fat cells causing uneven weight gain (for instance, if you got most of the fat cells sucked out of your ass, you would gain most of the weight everywhere but the ass, looking ridiculous. I have always been skeptical of these claims, but don’t really know. Hope this isn’t too much of a hijack. ---
**Author:** ![mr.jp](https://avatars.discourse-cdn.com/v4/letter/m/48db29/32.png) [@mr.jp](https://boards.straightdope.com/u/mr.jp)\ **Post date:** [August 6, 2006, 12:20pm UTC](https://boards.straightdope.com/t/when-you-lose-weight-what-do-you-lose-and-where-does-it-go/367535/6 "2006-08-06T12:20:58Z")
The overall system of metabolism obviously is not that simple. There are an awful lot of cycles and pathways. The whole thing gives us a proterin gradient, which is mostly used to create ATP (which is the body’s energy source). However, the bottom line is quite simple: Carbohydrates are broken down following this formulae: C6H12O6 + 6O2 -\> 6CO2 + 6H2O + energy. Proteins are broken down like this: protein -\> urea plus carbohydrate breakdown intermediate -\> urea + water + carbondioxide. So that’s pretty much it. Half water, half CO2, some urea. The water is urinated out, sweated out, or used again. The urea is urinated out, and the CO2 is breathed out. None of it is in the feces. ---
**Author:** ![mr.jp](https://avatars.discourse-cdn.com/v4/letter/m/48db29/32.png) [@mr.jp](https://boards.straightdope.com/u/mr.jp)\ **Post date:** [August 6, 2006, 12:37pm UTC](https://boards.straightdope.com/t/when-you-lose-weight-what-do-you-lose-and-where-does-it-go/367535/7 "2006-08-06T12:37:17Z")
Oh, I forgot fats. Trialglyceride -\> glycerol + fatty acids -\> glycerol + acetyl Those are both carbohydrate breakdown intermediates. ---
**Author:** ![solkoe](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@solkoe](https://boards.straightdope.com/u/solkoe)\ **Post date:** [August 6, 2006, 12:39pm UTC](https://boards.straightdope.com/t/when-you-lose-weight-what-do-you-lose-and-where-does-it-go/367535/8 "2006-08-06T12:39:22Z")
It’s not unlike asking “what happens to the gas in your gas tank?” It’s a chemical change and the fat is transformed into other materials that are expelled by the body. ---
**Author:** ![mr.jp](https://avatars.discourse-cdn.com/v4/letter/m/48db29/32.png) [@mr.jp](https://boards.straightdope.com/u/mr.jp)\ **Post date:** [August 6, 2006, 12:44pm UTC](https://boards.straightdope.com/t/when-you-lose-weight-what-do-you-lose-and-where-does-it-go/367535/9 "2006-08-06T12:44:18Z")
hmm, on second thought, I think I was wrong about the 50-50 water-CO2, it is probably more correct to say that a lot of the hydrogen is broken down into H+ which is used again. So, the answer to what leaves the body during catabolism is “mostly CO2, some water in amounts I have no idea about, some urea depending on how much protein is broken down.” ---
**Author:** ![Muad\_Dib](https://avatars.discourse-cdn.com/v4/letter/m/35a633/32.png) [@Muad\_Dib](https://boards.straightdope.com/u/Muad_Dib)\ **Post date:** [August 6, 2006, 1:53pm UTC](https://boards.straightdope.com/t/when-you-lose-weight-what-do-you-lose-and-where-does-it-go/367535/10 "2006-08-06T13:53:55Z")
So when losing weight you are mostly exhaling the flab away? ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [August 6, 2006, 2:00pm UTC](https://boards.straightdope.com/t/when-you-lose-weight-what-do-you-lose-and-where-does-it-go/367535/11 "2006-08-06T14:00:13Z")
And fat people are helping to fight global warming by immobilizing carbon that otherwise ends up as CO[sub]2[/sub] in the atmosphere? ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [August 6, 2006, 2:04pm UTC](https://boards.straightdope.com/t/when-you-lose-weight-what-do-you-lose-and-where-does-it-go/367535/12 "2006-08-06T14:04:58Z")
> [@Muad'Dib](#): > > So when losing weight you are mostly exhaling the flab away? Surprisingly yes. I had a thread some time ago that addressed the exact same question, but my mad SDMB board search skills apparenlty suck (or the search engine sucks). ---
**Author:** ![Civil\_Guy](https://avatars.discourse-cdn.com/v4/letter/c/d78d45/32.png) [@Civil\_Guy](https://boards.straightdope.com/u/Civil_Guy)\ **Post date:** [August 6, 2006, 2:26pm UTC](https://boards.straightdope.com/t/when-you-lose-weight-what-do-you-lose-and-where-does-it-go/367535/13 "2006-08-06T14:26:44Z")
> [@Xema](#): > > And fat people are helping to fight global warming by immobilizing carbon that otherwise ends up as CO[sub]2[/sub] in the atmosphere? I suspect that plants and trees are doing more towards that end. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [August 6, 2006, 2:29pm UTC](https://boards.straightdope.com/t/when-you-lose-weight-what-do-you-lose-and-where-does-it-go/367535/14 "2006-08-06T14:29:27Z")
> [@mr. jp](#): > > hmm, on second thought, I think I was wrong about the 50-50 water-CO2, it is probably more correct to say that a lot of the hydrogen is broken down into H+ which is used again. So, the answer to what leaves the body during catabolism is “mostly CO2, some water in amounts I have no idea about, some urea depending on how much protein is broken down.” Yes, you also have to account for the fact that some of the oxygen involved in comes from the air, and the different molecular weights of the atoms involved. In the case of fats, at least 70% of the weight of the fat leaves the body as carbon dioxice, and perhaps more. ---
**Author:** ![Beware\_of\_Doug](https://avatars.discourse-cdn.com/v4/letter/b/278dde/32.png) [@Beware\_of\_Doug](https://boards.straightdope.com/u/Beware_of_Doug)\ **Post date:** [August 6, 2006, 2:40pm UTC](https://boards.straightdope.com/t/when-you-lose-weight-what-do-you-lose-and-where-does-it-go/367535/15 "2006-08-06T14:40:00Z")
**When you lose weight, what do you lose?** Belly flab. **And where does it go?** Right back on. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [August 6, 2006, 2:55pm UTC](https://boards.straightdope.com/t/when-you-lose-weight-what-do-you-lose-and-where-does-it-go/367535/16 "2006-08-06T14:55:15Z")
> [@astro](#): > > After being metabolized a surprisingly large portion of the burned weight of fat is released as carbon dioxide through breathing. What I find surprising is that no one’s marketed a little breath CO[sub]2[/sub] monitor and an accompanying booklet describing foods and exercises that maximize ‘effective respiration.’ They could call it the air diet, or some such nonsense.