All in one weight in itself doesn't mean much in isolation. That's why you have people with a high BMI that are healthier than people with a "normal" one.
>An athlete at 240 lbs
As a contrived example, somebody this big (athlete or not), is probably at an increased risk of sleep apnea. I know of some competitive athletes (with visible abs, no less) that were surprised to learn they have sleep apnea. After a CPAP they felt better. Alternatively, they could probably have lost weight (but no longer be as competitive in their chosen sport.) Some of the risk factors (gender, neck circumference) aren't the typical proxies we use to subjectively assess health as a layperson.
>That's why you have people with a high BMI that are healthier than people with a "normal" one.
This can be true, but it is not generalizable. Last I heard, something like 1% of people with a high BMI would fall into this camp.
Like, at some point, dying, lower heart rate, loosing hair, being cold, your weins collapsing, body eating own muscles.
https://www.hsph.harvard.edu/nutritionsource/healthy-weight/
I suppose they could lose 10% through caloric restriction, but that wasn't part of this study.
Remember that pounds is a unit of force - not mass.
There's the set of "tech neck" images (example https://www.vital-balance.com/en/tech-neck/ though many more can be found) where it shows what the force on the neck is from the head. At 0°, it's 10-12 lbs of force down. If you've got your head tilted at 45° looking at a phone, the infographic says that its 49 lbs of force on the neck.
Additionally, when you walk or run you don't place only and exactly the force of the weight of your body down. Each foot is loaded with an impact and the forces are distributed up the leg. What your knee experiences is a dynamic and spiky load.
. . . "Our results indicate that each pound of weight lost will result in a 4-fold reduction in the load exerted on the knee per step during daily activities. Accumulated over thousands of steps per day, a reduction of this magnitude would appear to be clinically meaningful. " . . .