Fitness

Calories are a useful approximation, but not how humans actually operate. A Bomb Calorimeter burns material and the resultant heat generated is what we call a calorie. As a illustrative example of the difference - gasoline is very calorie dense, but not helpful if eaten by a human.

do I gain the calories over the next few hours? Or is it delayed a day or two?

The human body will break down all food and drink into its base components then decide what it will keep, what it will excrete (more or less). So when you consume something you "gain" it immediately (its in your system), the time until its used in the body could be minutes (like carbohydrates), hours (fibre), etc. Often the body will decide to store any excess (carbs again) for later use (weight gain).

Because there will be days when I eat almost NOTHING, and then my scale says I gained 3 lbs. But then there’s other days where I feel I ate like a slob, and somehow lost 2 lbs.

The human body is an amazing homeostatic machine, it's trying to self regulate to optimal body composition. The trouble is lots of modern western food messes with the bodies ability to self regulate..... which brings us to the real topic

Losing weight is hard, but it might be easier if I understood the rules of how this all works.

The big secret is hormones, don't interfere with your hormones and the body will self regulate body composition to optimal (lose weight if your obese).

[Paper] The Carbohydrate-Insulin Model of Obesity - Beyond “Calories In, Calories Out” - 2018

TLDR - Eating sugar and carbohydrates forces blood glucose levels to rise (within minutes), elevated blood glucose forces insulin to rise (to reduce blood glucose), elevated insulin forces the body to go into anabolic (gain weight) state. Basically you can't lose any fat while your insulin is high, so every time someone eats a bunch of sugar or carbohydrates with a meal/snack they are putting a 2-4 hour pause on any fat loss.

Some water "just goes through," but that never gets to your bladder, it's what keeps your poop moist enough to shit out. The water in your pee was absorbed through your intestines and colon, went into your blood, and may have flowed all around your body before eventually getting to your kidneys and washing some stuff your body didn't want out through your bladder and urethra.

Think of calories as energy stored. That drink has carbs in it. 1g of carb is approximately 4 calories. Liquid calories are much easier for your body to absorb than solid calories. Can't pee anything out until it gets processed.

You broke the code. The calories your body takes in on any given day are by definition like 99% balanced with the calories that go out, no matter what happens. Almost all of what happens to gain or lose weight comes down to what your body decides to do with it, whether to spend it right away and how much to spend at any given time and how much to save. Personally I think this is why intermittent fasting works well: It demonstrates to your body that the food source is 100% predictable on a very set schedule, which means it's probably organized and reliable, which means we don't need to hoard a bunch of extra energy in case one day there is no food.

If the amount going in swings up and down and strong hunger signals get ignored some of the time no matter what, then it's going to decide we're in crisis mode, and ramp way way down on how much energy goes to the organs, general maintenance, building stuff we need, running the brain so you can think and have energy, and instead it's going to just store it all so we can survive. And that's what most people who are trying to lose weight with a specific diet do, and that's why it doesn't work unless you push it all the way to the starvation barrier where your body physically can't expend any less calories, and starts burning the reserves and crossing its fingers. And then, of course, once you start eating again, you gain all the weight back because oh fuck what's going to happen next.

That's not to say you can eat a ton of ice cream every day and just have it be fine. Eating a normal amount of healthy food and exercising will do good for you. But in my opinion if you're trying to lose weight, strictly counting calories doesn't really work because your body can ramp down expenditure of calories way more easily than you can ramp down the intake.

Edit: Oh, also to answer the question: You're suspended in a roughly fart-density atmosphere all the time, so my guess is the weight you lose by farting will be cancelled out by the lower displacement of your new volume without the fart inside you. Basically it's like weighing a balloon: You only get the weight of the plastic, not the air, because the buoyancy of the whole thing cancels out all the weight of the air.

If you were standing on the moon, and farted and then vented the fart out of your space suit, you would lose the weight of the fart, same as weighing a balloon on the moon and getting the weight of the air too because there's no buoyancy to cancel it out.

Edit 2: I guess a balloon is heavier than air, because the air inside it is pressurized and so denser than the air outside, but you get my point I hope.