Is breathing a weight-loss program?

February 21, 2008 9:57 AM

Do we lose weight just by breathing?

Since we breathe in O2 and breathe off CO2, it seems to me that we are losing carbon atoms like mad each time we breathe out. This assumes, of course, that for each O2 breathed in a CO2 is breathed out, a straight one-to-one exchange, and that's a huge assumption. Is it correct?

posted by Camofrog to science & nature (9 comments total)

You do lose weight when you breath. But not just carbon, you also exhale water vapor.

This was actually an important scientific discovery about 240 years ago. It was known that the quantity of excrement produced by animals didn't mass as much as the quantity of food and water they consumed.

Lavoisier was trying to push the idea of "conservation of mass", and one of the things he had to do was to put animals in sealed containers to show that the mass didn't change once you took into account the air they breathed out. BUT when you opened the chamber and let air circulate freely, the mass dropped immediately.
posted by Class Goat at 10:05 AM on February 21, 2008 [1 favorite has favorites]

Well, you're not really wrong, you do lose "weight" from expiration. You do lose carbon and oxygen atoms as well as a bunch of water and other stuff. In fact, if you put ventilated ICU patients on a high-carb diet, it can wreak havoc on their CO2 status. There are a few problems with respiration as a weight-loss strategy, though:
1) When you breathe in, you're breathing in more than pure O2. That's good, because pure O2 is not so good for you. So you're gaining more than 2 oxygen atoms.
2) As you suspected, it's not a one-for-one exchange. We breathe because we need and use the O2, not because we need a vehicle to get rid of carbon.
3) You have an issue of scale happening here. Compared to the composition of solid tissue, the mass of respiration is negligible.

On the other hand, if you have a really, really precise scale, you probably should weigh yourself after blowing out really hard. :)
posted by LittleMissCranky at 10:15 AM on February 21, 2008

"for each O2 breathed in a CO2 is breathed out, a straight one-to-one exchange,"

That isn't strictly true either. Your body doesn't use most of the oxygen you breathe in. That's why mouth-to-mouth works; there's still plenty of oxygen in your exhaled breath, though not quite as much. Poor Lavoisier was trying to measure some tiny amounts there.
posted by i_am_joe's_spleen at 10:18 AM on February 21, 2008

There is actually an exercise program that promises weight loss through, well, heavy breathing. I have doubts about how well it works, though. :)
posted by JanetLand at 10:20 AM on February 21, 2008

Thanks for the answers!

To clarify, I was not seriously considering this as a weight-loss program (for one thing, I'm not overweight). I was merely curious because I can (temporarily) lose 1-2 pounds each time I work out. I assumed most of that was water, but I wondered how much could be off-gassed carbon.

Poor Lavoisier was given the guillotine weight-loss program for his efforts.
posted by Camofrog at 10:42 AM on February 21, 2008

Breathing, along with heart beating, kidneys making urine, thinking, and all of the other functions of your body that don't involve exercise make up your basal metabolic rate. You can lose weight without exercise if you taken fewer calories than this, but it would be a pretty strict diet.
posted by TedW at 11:01 AM on February 21, 2008

...for each O2 breathed in a CO2 is breathed out...

As mentioned above this is not true and it varies with diet; there is also a number for this: the respiratory quotient.
posted by TedW at 11:04 AM on February 21, 2008

Speaking of thinking, the O'Reilly book Brain Hacks has a bunch of neat DIY psychology/neurology experiments. In one of the early ones you lay on the couch and do your best to think about nothing. Your friend takes your pulse and then gives you a mental task to perform. They say you should expect about a 20% increase in your pulse which kind of surprises me.
posted by Kid Charlemagne at 1:23 PM on February 21, 2008

By some estimates, aerobic metabolism is 19 times as efficient as anaerobic, so perhaps there is an argument to be made that not breathing is a better way to lose weight.
posted by jamjam at 1:30 PM on February 21, 2008