There actually is one excersize routine that one can do that will completely ignore/offset your diet. Competitive swimming. There is an issue. If you eat empty calories, you feel and perform like shit. Yeah, at my peak I was eating 20,000 Kcal a day, but there was no processed sugar, no bleached flour, no soda, no dyes, you basically had to make everything from scratch.

Fitness is 70-80% your diet.

Arrr these goah darn genes.

People either ask me how i'm staying thin or just straight up tell me that i'm lucky. When i tell them that i eat healthy and don't drink and so on, i already loat them, they don't actually wanna hear that. They wanna gear something like: oh i just take this magic pill every morning.

But on the flipside that's pretty much all I eat and I'm skinny AF also I usually lose weight when I eat only fastfood like when dominos had a voucher exploit for a whole summer as a kid

Edit: js found out from another comment its probs my anxiety stopping me from gaining weight

No, but running a deficit becomes much harder, when your body ingress all the calories from all food sources and has a low metabolism.

Some people are like "yeah, I lost weight by skipping my snack apple in the evening" while others would need to skip 2.5 meals per day. So the latter have a much harder time to maintain a deficit for long enough.

I'd say that the genetics are probably more along the lines of "no off switch for wanting to eat." I.e. you just keep bingeing calories.

Nope. It's usually people, like in this thread, not understanding what "bad genes" means.

You're a thermodynamic machine, not magic. If you eat less then you burn you'll loose weight.
You are also an extremely complicated machine, with complex chemical processes that govern long and short term behaviors.
"You" are a little slice of protein and fat the size of an avocado glued to the front of a more complicated machine. "You" are responsible for solving problems. The rest of your brain and endocrine system is responsible for managing most desires as well as most other things.

Some people have genetics where they run a mile and their body says "oh shit, this would be easier if I turned the energy fountain up to full wouldn't it?" And now they're burning more energy when they're asleep than they were before.
Other people have genetics that gives them a body that says "oh my God, you just ran nearly 2 blocks. Clearly you're in danger, so I'm going to increase the hormones that tell you to eat a lot more food. Don't worry, the pizza will be gone before you actually feel how much food that is".

You can override the endocrine system, but it's hard. The frontal cortex can change what you do, but the endocrine can change what you want.

Your body is a machine, just like a car. And different cars will start to ding and nag the driver for fuel or maintenance tasks at different points, with different levels of intensity. If your car is built for the Australian outback it might be way more aggressive about fuel warnings, and have a significantly larger tank.

All that's why excercise is a terrible way to lose weight. You lose weight by getting your eating under control and convincing the medieval peasant in your endocrine system that you're not in a famine. Excercise makes your body feel better, more capable, and healthier.
You can excercise all you want, but you can eat your way through any excercise routine in minutes.
A peanut butter and jelly sandwich is more than an hour of vigorous time on a rowing machine.

A lot of calorie expenditure is determined by hormones, and for a typical person, resting metabolism is a significant percentage of total calorie burn.

Some people respond poorly to dietary interventions because they end up with lower resting metabolic rate. Sometimes it shows up in the form of a person who is always feeling cold or exhausted.

Others have high stress hormones, which throw all sorts of metabolic loops out of wack.

And other hormones affect appetite or satiety after eating, so the biological disadvantage (whether genetic or environmental or both) sometimes comes in the form of greater difficulty with portion control or willpower compared to others. That's not a direct effect on calories in versus calories out, but it does have an indirect effect on overall success with a weight loss program, and it's grounded in an actual physical/physiological/biological difference between individuals.

Our bodies each have an equilibrium of calories consumed/burned that it really wants to be maintained. If you start dieting to reduce calories consumed, then it automatically adjusts so that your body burns fewer calories just for existing, thereby reducing the deficit you created with your diet. So people see the diet not working and give up rather than taking the time to dial in a sustainable dietary calorie deficit that allows for weight loss without leaving you physically and mentally exhausted by your bodies compensatory reaction.

It does seem to be a thing. Just not as common as some people want it to be.