@tsinnc
It does seem to run in some families, but if one looks back to the 70s for instance, or at least photos from that time, it is apparent that there were few overweight people.
The modern rise in obesity tracks the widespread availability of fattening foods, and the decline in what one might term 'proper' cooking, that is to say cooking from scratch. This began a good few years ago, so we now have a generation where their parents never cooked nor ate well, and lacking a good example people have grown up (and outwards) not knowing any better. I was fortunate that this was not the case for me, and my wife has always cooked from scratch, I was and am lucky.
As regards exercise, I'm sure it's harder to exercise when one is carrying more weight. I would never wish to deter anyone from exercising, it's good for the heart and general muscle tone, but its role in weight loss is overstated, perhaps because of a reluctance to point to someone's diet as a cause of their weight.
To burn off the calories of one slice of bread for instance, one has to walk briskly for around 20 minutes or run 12 minutes. How long to burn off a slice of cake or a few biscuits... it's not going to happen.
Exceptions apply, as you say, but for most people the route to weight loss is to eat less and eat better. We should be glad that it is something most people can remedy without medical intervention.
Whether that helps with PN is another matter of course, but it would at least help with the leg weakness that often arises from PN.