We might know the inner workings of the "machine" but we can control inputs (food) and measure outputs (weight).

Let's say I eat 3 hamburgers per day and gain ~1kg per month.

If I reduce that to 2 hamburgers per day I maintain my weight.

And when I reduce that to 1 hamburger per day I lose ~1kg per month.

That is simple. As for how I feel while eating 1 hamburger that's another question.

I can try to improve the machinery of my body by e.g exercising, eating healthier food, adjusting my macros, taking supplements, etc.

So now I can eat 1.5 hamburgers per day and I feel better and still lose 1kg per month.