Training & Nutrition - Where does all the mass go?

Ok when I bike 2 hours and burn 1800 calories, that's physically 1800 calories of stuff. But I don't poop that much stuff physically. Aside from the water, where does all that solid mass go? What exactly happens physically when I "spend" 1800 calories?

Heh, you said "poop" :)

For real, though, I have wondered this same thing myself.

You use your cals to propel you... think of it as "energy" ;)

You use your cals to propel you... think of it as "energy" ;)

Hehe yeah but those cals come from food, physical mass in food, all that mass has to go somewhere...

I'm not sure if I'm understanding you right... but think of it like this maybe: you put a tank of petrol in a car, it has mass and volume, right? where does it go? it's converted into different energies, some of which is used to propel the car. A lot is lost as heat byproduct. But in the end, after you drive around a lot, you have an empty tank - but you certainly can't account for it just on what came out the exhaust pipe (although with some cars...).

(egads. I feel dirty using a car as an analogy :( )
that help at all?

Well like, if I eat 3 kg of food a day, physically it's about 1-1.5kg water. So there's still 1.5-2 kg of physical mass there. Now if .5-1kg of mass comes back out the "tail pipe", and I exhale say .5kg of mass, there's still .5-1kg of mass that's unaccounted for somewhere. I sweat but that's mostly water, where does all that extra mass go if I'm not gaining any weight.

Think of it this way. I heat my house with wood. I carry in some mass of wood and carry out a much smaller mass of ashes. I've never measured the mass of the smoke and crud that builds up in the chiminey, but I'll bet it comes close to adding up.

I know what's bothering you the sweat - 1 it's not just water, but minerals and other stuff. Also in converting food to energy water must be some of the byproduct. So if you measured all the inputs and all the outputs they sould be very close to equal since even if you believed some mass was converet to energy it would be a tiny amount.

Joe

gah!!
remember highschool biology / chemistry
CARBON
as in Carbon dioxide :)

you give off:
sweat (water and various minerals)
Heat
CO2

think back to that story you read in your school books about the experiment with the tree, water and potting soil. Van Helmont or something.

I guess I have a hard time visualizing THAT much carbon being given off in my breath.

LoL. well if you've ever seen me huffing and puffing going up a hill...

Let's be scientific about this! Eat exactly 100 kernels of corn.. then 8 hours later count the...

It burns up just like any fuel, hence the smoke coming out of your ears. Either that, or you are thinking too hard about this.

Ok when I bike 2 hours and burn 1800 calories... Aside from the water, where does all that solid mass go? What exactly happens physically when I "spend" 1800 calories?

I am trying to recall basic chemistry, but I think it goes like this--

When you burn anything, such as firewood, or food, you're basically converting relatively large organic molecules (with a lot of carbon) to carbon dioxide and water. As those large molecules are broken down, some of the energy inherent in the chemical bonds holding them together is released as heat. Whatever solid stuff your body doesn't break down is passed out -- as we would say on a road trip -- via #2, while other odd by products of the process leave your body via #1.

I'm sure there are doctors or physiologists on this list who can correct me on the details, but your body is basically a chemical processing plant. Bon appetite!

Let's be scientific about this! Eat exactly 100 kernels of corn.. then 8 hours later count the...
Ewww...
Most of it is converted into heat.

Ewww...
Most of it is converted into heat.

Actually, none of it is converted into heat. The heat comes from the breaking of chemical bonds and does not affect the mass of the compounds involved (except in nuclear reactions, which we are not talking about here). The Law of Conservation of Matter states that mass IS conserved in a chemical reaction, which is what happens when we "burn" food for fuel. The mass of the food you eat, plus the mass of the oxygen you breathe, and the water you drink will equal EXACTLY the mass of the waste, CO2, sweat and urine that you produce.

Actually, none of it is converted into heat. The heat comes from the breaking of chemical bonds and does not affect the mass of the compounds involved (except in nuclear reactions, which we are not talking about here). The Law of Conservation of Matter states that mass IS conserved in a chemical reaction, which is what happens when we "burn" food for fuel. The mass of the food you eat, plus the mass of the oxygen you breathe, and the water you drink will equal EXACTLY the mass of the waste, CO2, sweat and urine that you produce.

Yeah I remember chemistry now the equations we did where you have a pile of stuff at one end and youve to work out what comes out, its always exactly the same. Matter is enegry tho E=MC^2 but thats nuclear stuff....

It goes up in smoke, like bacon fat frying on the grill.

I know that after a 2 hour ride I can scrape the salt off my arms, legs, neck and forehead. There's probably a few grams of salt right there.

Well, when you exercise your body uses the chemical energy in either carbohydrates or fat to form ATP from ADP. The ATP can be used by muscles for contraction forming ADP. Most of the time, the fat and carbohydrates are just burned. That is carbo or fat plus oxygen to get carbon dioxide (which you breathe out) and water and you use the energy liberated to form ATP at about 33% efficiency and the other 66% of the energy is just heat.

Now you seem to be confusing respiration with digestion. You mentioned "poop" which is a slang term for feces. When you eat something, it goes into your gut. Your gut using chemicals attempts to break the food down into components which are hopefully absorbed by your body and used. But you can not digest everything like fiber so what is left over comes out the other end. The thing is that stuff in the digestive system really is not inside your body per se. The interior of the digestive system is still outside of your body in the sense that a donut hole is outside of the interior of the donut. The digestive system has all sorts of wild and exotic flora in it. That is why if the digestive tract is pierced in a deep wound, people get peritonitus. All those bacteria suddenly get access into the body rather then just running around in the interior of your gut.

The whole point of this is that while you originally formed your carbohydrates and fats from things you ate, you can store up quite a bit of energy and ride an astounding distance potentially on your existing reserves. A single lb of fat would motor a reasonably big guy about 70 miles down the road. Now in practice, most people eat before and during a long ride but digestion in most people takes some time so you don't see the results during the ride. Also when you are exercising vigorously, the body pretty much shuts down everything but essential services and that includes digestion.

No wonder Ive been losing about a 1/4 pound a day . Last week I wieghed 230 , 4 days later I weigh 226 . I got about 10 more to go before I get my 6 pack LOL . Ive lost over twenty pounds in less then two month . It seems like its accelerated within the last few weeks . I love biking .
jarhead#42

I guess I have a hard time visualizing THAT much carbon being given off in my breath.
3lbs per cubic yard at sea level and 70f which is very roughly 1.5 kilograms per cubic meter(1000 liters) at 22 degrees centagrade.
At a normal 4 liter lung capacity and 30 breaths per minute thats only 8.3 minutes per cu meter. Of course exhaled air only has about 5% CO2 so it would take 166 minutes to breath out 1.5 kilos of CO2 assuming full breaths. 1.5Kg of CO2 is worth about .5Kg of carbon which is the bulk of the weight in absorbed food.
So when all is said and done its about 3 hours to breath out a pound of carbon and at 20mph thats 60 miles which is close to the 70 miles per pound of fat figure that Pat gave only less accurate as I came to it the long way all the while rounding and roughly converting.

Now some trivia:
It is the build up of CO2 that causes you to surface for air when holding your breath not the lack of oxygen. This is why you will not breath any different when in pure nitrogen(air with no O2) but you will pass out and die just the same.