A couple of things I don't understand about weight loss

You breath in oxygen. O2. You breath out carbon dioxide. CO2. That carbon atom is where your weight is lost, in that exchange, through respiration.

The answer to "where does a plants mass come from?" Is the same answer in reverse.

Yes I know there is also nitrogen exchange but carbon from respiration is the primary source.

So short answer...where does the weight go? You breath it out.

Fancier answer food is primarily hydrocarbons with some nitrogen. The oxygen and hydrogen that aren't incorporated into your own macromolecules are formed into H20, water, and excreted in urine. Nitrogen waste is converted to uric acid and also goes out as waste. Undigestables go out as solid waste. Carbon waste goes out via your breath.

Fat is pure hydrocarbon, no nitrogen. You burn fat you convert it to water which you excrete and carbon you breath out.

pebble4321 wrote: »

Oh, that is the best answer ever. I've read the same kind of thing lots of times, but the simplicity of this is beautiful.
Thanks AaronK, you are a genius at making science stuff understandable!

Any elegance is nature herself my friend.

FrumMama wrote: »

1) How does weight actually "get lost." For example, if I weigh myself and I weigh 100 pounds (yeah right). And then I eat a 16 oz steak, a pound of potatoes, and a pound of green beans. I should gain three pounds, right? But there's not necessarily the same amount of calories in each of those, so I'll probably end up gaining more from the steak than the green beans. Why? Isn't the steak still in me?

Right after eating them, you would weigh more or less 3 pounds more. Yet, right away your body starts to digest them and extract the nutrients and energy from them. That takes energy as well. You are correct that the amount of energy you would get from eating say the steak compared to the beans would be different because there is more energy stored in the steak than in the beans largely because of the fat content. (4 calories per gram of protein and carbohydrate compared to 9 per gram of fat), but it really comes down to how your body uses that energy. Some will be used to do things like digest your food, keep your heart beating, and the rest. That energy is used and results in CO2 being breathed out, so it doesn't become fat. Some is stored in your liver and muscles as glycogen to be used later as a quickly accessible energy source, and some will be stored as fat. As digestion does its work the matter has energy extracted from it, and it is used in these various ways by the body, and what cannot be digested comes out the other end as waste.

2) How does weight "get gained"? For example, at night I weigh myself and weigh 100 pounds (yeah right). The next morning, before eating, I weigh myself and weigh 101.5 pounds. How does that happen?? This just happened to me the other day. How does this make sense?

Weight gets gained for various reasons, but the only one really important is fat storage which happens when the energy (calories) you eat that are extracted by digestion exceed the amount needed to maintain your body and power your daily activity and exercise. Weigh can also go up because of water being retained either because a person ate more sodium than they usually do and the body retains water to deal with it, or they have exercised more intensely or a different exercise program than usual in which case water is used as part of the process of repairing the micro damage to muscles so they become stronger and able to do things better. It also goes up if food is going slower through your digestive tract due to lack of fiber, too little water or fat or maybe even an large meal that was within your calorie goal, but needs longer to digest. That stuff still digesting has weight as well.

So your 100 to 101.5 could be a whole host of things. Assuming no further consumption of food or water, it is sort of confounding, but I personally would think it is just the inaccuracies of the average scale. The scales available at the store are not super accurate and many things can cause small inaccurate readings and 1.5 pounds would be considered that.

3) What does exercise do? Again, there's this "Law of Conservation of Matter" thing we learned in high school. Stuff doesn't just disappear. So how do we lose weight?

Exercise takes the energy in your body and turns it into motion. The resulting process that Oxygen in and exhales Carbon Dioxide and that Carbon atom added is primarily where that "mass" goes. It isn't created or destroyed it just changes state in a way that leaves your body.

Sorry if these are stupid questions, I just don't get it.

Not stupid at all.

You might find this interesting. Kind of "shows" what posters above, especially @Aaron_K123, have been telling.
https://youtu.be/vuIlsN32WaE