When we work off weight, where does it go?

I’m thinking that the essential metabolites of energy production in our cells are water and CO2. Maybe a few other trace materials that get excreted. But where does the majority of the weight go when we work it off? Water and CO2?

Going back to my anatomy and physiology days, there is also the glucose that is produced by breaking down the fat cells and used for energy.

You burn it. Fat cells release energy to make the rest of your body go, just like gasoline in a car.

Yes, Cat, but the glucose is still *inside *you. It’s when it gets broken down into water and CO2 and it leaves your body, is when you lose weight, I believe.

But the gasoline doesn’t just disappear. It gets turned into water and CO and CO2 that leaves the car. Your car is lighter when you go from a full tank to empty because the gasoline was broken down and left the car (while some energy was released.) My question is what are the weighy products of metabolism that we lose when we “work off weight”?

Yeah, that makes sense. (Digging in the memory banks again) - it gets turned into all of our excretory products - water, C02, urea, nitrogen, all the rest of the metabolized molecules that we pee, sweat, and breathe out.

The glucose (C[sub]6[/sub]H[sub]12[/sub]O[sub]6[/sub]) in your body is oxidized by inhaled oygen and converted into CO[sub]2[/sub] and water that leaves the body. You exhale the CO[sub]2[/sub]. You excrete or sweat out the water.

The net chemical reaction is:

C[sub]6[/sub]H[sub]12[/sub]O[sub]6[/sub] + 6O[sub]2[/sub] -------> 6CO[sub]2[/sub] + 6H[sub]2[/sub]O + energy

Note, by the way, that the lungs are the primary excretory organ in the human body. We breathe out far more waste than we pee or poop out, which in turn are far greater than what we sweat out.

The majority of the mass that makes up fat molecules is excreted through the respiratory system as CO[sub]2[/sub]. Most of the rest is water.

Thank you.

Just thought I’d point out that fat does not get converted to glucose in normal human metabolism. A few plants are capable of it mostly so that seeds can store fats and use them to make cellulose for quick growth, but not people.

But you’re right that the ultimate end product of both fat and glucose is CO2 and H2O.

Some of the energy is also converted into heat that is radiated from your body.

A fat molecule consists of carbon, hydrogen, and a small amount of oxygen. (Sugars and other carbohydrates also consist of carbon, hydrogen, and a rather larger proportion of oxygen. Some fats also contain a little bit of phosphorus, but that is not, for the most part, the fat that makes you fat or that gets burned when you exercise.) When you burn it to get energy to move your muscles, the carbon and hydrogen combine with oxygen from the air to make CO2, which you breathe out, and H20, which you lose in a number ways, primarily peeing, sweating and breathing out again. That is where the weight goes. To all intents and purposes, that is where all of it goes.

In practice, we also burn some protein when we exercise too. Protein molecules consist of carbon, hydrogen, oxygen and nitrogen (with a tiny proportion of sulfur and phosphorus). The carbon, hydrogen and oxygen all combine with more oxygen to make water and carbon dioxide again. The excess nitrogen is peed out as urea, and any excess sulfur and phosphorus will also come out in the urine (probably as sulfate and phosphate salts).

Energy itself does not weigh anything.

Doesn’t it? Energy times a really big number = mass, right?

Energy = mass times a really big number

Y’all are wooshing us, right?

I’m sure you remember some fuzzy headed german guy a while back who came up with:


E - Energy
M - Mass
C - Speed of light

One kCal masses on the order of 10^-11 grams, according to my calculations. You’re not going to win on The Biggest Loser by relying on relativistic mass/energy conversion effects.

Sure, energy is equivalent to MC^2. That doesn’t mean that your body heat is MC^2. I have 5 Washingtons in my wallet right now, $5. That doesn’t mean I can close and reopen my wallet to find a Lincoln in there.

For the same reason, if I beef up your body heat by, i dunno, putting a heater next to you, you’ll weigh X. If I transport you to the walk-in freezer, you’ll still weigh X.

It goes to live with Jesus :slight_smile:

That’s right Jeus’s friends are bunch of fat blobs

Al Gore says “Don’t Diet!” :slight_smile: