I don't get why folks often need to reduce such a complex and unique system as our body and its metabolism into some few word description.

You are correct, and there is more, much more: psychology, how our body adapts to training, and so does metabolism. One random example of this vast topic - its well known in weightlifting community if you do hard compound exercises near your limits (squats, deadlifts etc) your metabolism switches to 'higher' burn rate (basal metabolic rate IIRC) and you can basically consume more. One sure way to lose weight if thats the goal, but one should never start weightlifting with those exercises, at that intensity.

Also, again generally, its pretty non-smart to take sedentary individuals and expose them to HIIT as the study did, even if its just spinning. Body should gradually adapt to workload (=stress) and HIIT should be the final step in training, since its so taxing. Otherwise injuries and lose of motivation will happen more often than not. The systems that need adaptation are numerous - muscles, tendons, ligaments, cardiovascular system, nervous system etc.

People are just looking for quick solutions to problems that don't have ones, not good long term at least. Same as diet fads. The cold hard truth that permanent change of fitness/BMI/overall health for the better requires permanent change in nutrition, training and TBH at least a bit overall life approach. Why not start with that?

>People get hungry after exercise and automatically eat more to compensate for the spent calories.

This isn't universally true.

Exercise significantly decreases my appetite for about 3 hours post exercise. And for me, it's not just a barely noticeable decrease - it's an extremely noticeable long-lasting appetite decrease where I'll often end up skipping meals.

Do a quick google search for "exercise decrease appetite" for supporting evidence.

During the exercise the body is in a state of flight or flight[0], the other mode is rest and digest. So during hunger will go away, but the body will want to be able to exert the same or more(because that amount was at least needed), and as such it will start fighting against rapid weight loss by exercise, by increasing hunger, and or slowing metabolism.

The reason why this is quite simple, body is unable to see the difference betweenexercise and staying alive in a hostile world. As such staying alive will always be prioritized. If CICO would work then we wouldn't be obesity pandemic[1]

[0]https://en.wikipedia.org/wiki/Sympathetic_nervous_system [1]https://pubmed.ncbi.nlm.nih.gov/28292617/

That sounds neat.

For me, after I exercise, I get ravenously hungry and am unable to concentrate for the rest of the day unless I eat a 3-5k calorie meal. I heard it would get better over time, so I did it for a year, one hour with a really good personal trainer, three times a week. It put a lot of strain on my relationships, and I got in trouble at work since I was basically at half capacity, and couldn't get any work done on Mondays, Wednesdays, or Fridays. I did it for a year and it was the same the whole time. I was also told that eventually I would get "addicted" to exercising, but I hated every moment of it up to the very end.

After a year of that, I stopped, and regained my sanity for the most part. I didn't actually lose much weight, but towards the end I had gotten some compliments about looking healthier, which was nice, but not worth the psychological tool it took on me. I guess I'm just sitting here desperately trying to not destroy my body further while I wait for some miracle cure for leptin resistance or something.

That's rough.

3k-5k calorie meal? That's an entire day's worth of calories, for someone really active. Strange your body didn't adapt.

I would be writhing in pain if I attempted to consume 3-5k calories in a sitting. I consume a lot of calories on basis that I also burn a lot cycling, but nowhere near that in a sitting. Even 5k/day for me would be painful.

I can consume 3k a day eating clean, but no more.

Eating all that in one meal would require some extremely unhealthy eating, for me.

I know sumo wrestlers and other extreme athletes are capable though.

3k-5k calories is 3 big burgers with fries, or two pizzas.

If GP is eating that much, they are very overweight. You don't burn that much calories during exercise, unless you are running a marathon (which I would not recommend doing 3 times a week).

3k-5k isn't a normal day, it's what happens during a binge. I would almost never do that after a workout, I would usually just writhe in pain from the hunger for the rest of the day. I rarely go over 2k calories during a normal day, but after a one hour workout, 2k calories doesn't even slow me down.

Interesting, thanks for following up and sorry for making assumptions. It seems we're all different. After a one hour workout I do get hungry, but not that hungry. I wonder if it's just different between people, or if the type of workout makes a difference -- I usually run or ride a bike at medium intensity, maybe it's different if you lift weights or do something more taxing?

First, this heavily depends on how exactly you exercised and on your actual diet. Bulking makes you hungry. Mild cardio or runs makes you less hungry and less likely to just eat crap.

Second, your body is rebuilding and healing itself from micro injuries, so eat proteins if you are hungry at that time. That does not mean your dinner then has to be exactly the same as before, you just have to shift when and what you eat.