A lot of this is because people had to do a lot more exercise during the day than we do now. Not that the lard was better for us. This is where a lot of the downvotes come from. Even the rich had to do a lot more walking. If we could return to the amount of exercise we averaged 50+ years ago, you would see a lot of this decline. The next big thing is the amount we eat. We consume significantly more calories now than we used to. In the past 100 years it has increased ~20%. All the while we have been doing less physically. The third big factor is where the shitty food comes in. Having sugar/highly refined carbs added to just about everything promotes over-eating, while also fucking with your insulin production, and other endocrine issues, that promote fat retention, while also increasing addictive eating disorder likelihood.