Question for the biologists out there

bradp1979

Ok, maybe someone can clear this up for me. We all know that if you burn more calories than you consume, your body will use either muscle or fat as its energy source. If less weight is gained through muscle growth than the muscle or fat stores used for energy, then you will weigh less. My question is this: why?

When fat is used for energy by your body, sure your face, stomach, butt, etc. will be less round, but why do we weigh less? Let's just say that the calories within some fat stores are utilized by say, the brain. So the fats are metabolized by your body to create the calories (energy) your brain needs to continue working. However, aren't the component parts of those fat cells still in our body? It's not like we have an exhaust pipe (no fart jokes, please,) so even though those fat cells are used as energy, the component parts of those cells still exist in our body, although perhaps in the form of individual atoms. Once something is metabolized by a larger organism shouldn't the overall mass stay the same, with only the dimensions being different?

This has quite literally given me a headache trying to figure it out.

amusedmonkey

Too sleepy to explain and need to go to bed so I'll tell you this until someone else comes to elaborate. You actually do have exhaust pipe, it's called lungs. You exert metabolic waste through organs such as lungs, kidneys, skin.. etc

earth_echo

Mass–energy equivalence or E = mc2. The mass of an object or system is a measure of its energy content.

When fat is burned by the body, it's mass decreases... just like a burning log loses mass as it burns. Basically, the fat in your body is turned into heat and heat has no mass.

SingRunTing

When the fat is broken down, it's used for energy (gets consumed) and results in waste byproducts. The waste byproducts of all that metabolizing get excreted via peeing, pooping, sweating, respiration, etc.

LAT1963

Actually, we do have an exhaust pipe--our lungs.

Fat is made of primarily of the elements carbon, oxygen, and hydrogen. When fat is broken down, the carbon leaves the body as CO2 gas, where the oxygen and hydrogen leave the body as water.

The energy that formerly bound those elements all together in the form of a fat molecule is where we get the power to move around and run the rest of our cellular processes.

3laine75

Mass–energy equivalence or E = mc2. The mass of an object or system is a measure of its energy content.

When fat is burned by the body, it's mass decreases... just like a burning log loses mass as it burns. Basically, the fat in your body is turned into heat and heat has no mass.

^this

More physics than biology

LAT1963

Mass–energy equivalence or E = mc2. The mass of an object or system is a measure of its energy content.

When fat is burned by the body, it's mass decreases... just like a burning log loses mass as it burns. Basically, the fat in your body is turned into heat and heat has no mass.

No, E=mc^2 only applies to nuclear reactions and matter-antimatter reactions.

Add: life occurs at the level of chemical reactions, not nuclear reactions. The basic flow of energy is this:

nuclear reactions in the sun-->

light comes to earth-->

plants use light to power making carbohydrates out of CO2 and H2O in order to store the energy from the light-->

animals eat the carbohydrates and break them down to release the energy put into storage by the plants-->

(some animals cheat by eating other animals to get the energy gathered by the animals from the plants-->)

animals excrete CO2 and H2O-->

plants use the CO2 and H2O from the animals to store the energy from light from the sun-->

repeat...


The sun's nuclear energy in the form of light is stored in the chemical bonds of carbohydrates, and our entire ecosystem occurs by shifting those chemical bonds around to release that light energy in tiny quantities until all that's left is CO2 and H2O.

WalkingAlong

...so even though those fat cells are used as energy, the component parts of those cells still exist in our body, although perhaps in the form of individual atoms.

I'm not a biologist but if it helps (in addition to the above), we have a finite set of fat cells. When you burn fat for energy, the cell doesn't get removed, the lipid content gets removed. So our fat cells shrink. The number doesn't change. Unless you get liposuction.

What happens to the lipid or other matter used for energy is like what happens to the gas in your car's tank. Heat, emissions and kinetic energy!

lindsey1979

Actually, we do have an exhaust pipe--our lungs.

Fat is made of primarily of the elements carbon, oxygen, and hydrogen. When fat is broken down, the carbon leaves the body as CO2 gas, where the oxygen and hydrogen leave the body as water.

The energy that formerly bound those elements all together in the form of a fat molecule is where we get the power to move around and run the rest of our cellular processes.

+1. Spot on.