Paleo Diet and Paleolithic Diet Questions & Answers

Question

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People throw that phrase around all the time, "We're burning fat." And I understand much of the physiology involved, but where does the fat go after it's metabolized?

Do we sweat it out?

Does it pass through the urine or feces?

This question becomes even more absurd if you consider the fact that I have a Bachelor's degree in Exercise Science and Master's degree in Sport Mgmt., lol.

edited Sep 26 2010 at 21:39

sean
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asked Mar 5 2010 at 5:57

TheUnbreakableOne
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Acton · Answer 1 · 2010-03-05 06:06:46Z UTC

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After fatty acids are metabolized, they are CO2 and water.

answered Mar 5 2010 at 6:06

Acton
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	Really? We don't poop it out? I have no idea. I'm just askin'... – gilliebean♦ Mar 5 2010 at 7:48
	Acton, you are a veritable encyclopedia of information! – henny Mar 5 2010 at 16:30
	The stuff in our poop is what never crossed the gut in the first place. At least according to my very primitive understanding of things. – Mister B Mar 6 2010 at 2:30
	Poop is mostly bacterial cells by volume, the remainder being roughage. – Acton Mar 6 2010 at 4:13
	If you're pooping it out, it's undigested dietary fat, not burned body fat. – maryeeclarkisouthunting Sep 11 2011 at 16:36

Gary Wu · Answer 2 · 2010-03-06 01:48:57Z UTC

The Wikipedia article on fatty acid metabolism contains the full answer to your question. To summarize in laymen's terms:

fatty acids are broken down into acetyl-CoA molecules
acetyl-CoA is consumed in the TCA cycle
the TCA cycle uses acetyl-CoA + 2 H2O + stuff to produce 2 CO2 + energy + stuff

From Acton's comments below:

"Water is yielded in overall fatty acid oxidation. You left out the most important part, the electron transport chain, where the bulk of the energy is actually produced. Reduced protons from beta oxidation and the Krebs cycle donate their electons to oxygen via the electron transport chain to form water, producing ATP. "Burning" 100 grams of fatty acids produces roughly 100 grams of water."

If you're asking about the fat that we eat but don't store on a low-carb diet, some of the fatty acids get broken down into ketone bodies, and the ketone bodies can be expelled through breathing (keto breath) or expelled through urine. I believe both of these are rather minor amounts, however; most of the fat is converted to energy, making you feel "more energetic" and/or boosting your body temperature.

Dexter · Answer 3 · 2010-03-06 17:02:37Z UTC

Dr Eades, in his newsletter email, references his response to a question by Ryan http://www.proteinpower.com/drmike/weight-loss/a-legitimate-use-for-orlistat/ from 2007 regarding "Where does the fat go." It is buried in the comment section.

Richard Nikoley references the same at http://freetheanimal.com/2010/03/isnt-it-time-for-anthony-colpo-to-get-a-life.html in his blog about Anthony Colpo and Dr Eades.

Edit: Dr Eades ties the whole thing up at http://www.proteinpower.com/drmike/metabolic-advantage/thermodynamics-and-the-metabolic-advantage/#more-4034

Mikael Jansson · Answer 4 · 2010-03-07 11:02:18Z UTC

There is no functional difference, in terms of what eventuall happens, between the fat you've got stored in your fat cells and the fat that you ingest through your mouth.

In fact, most fatty acids you eat are first transported to your fat cells and then used.

lhahne · Answer 5 · 2010-03-05 08:17:56Z UTC

The amount of fat cells stays almost the sama for all adult life. The fatty acids themselves disintegrate into CO2, water and energy (heat). The CO2 is breath out and I think you can guess how the water comes out. Energy is used by the body.

Stupid Question: So we’re losing fat, but where does it go?

5 Answers