You mentioned obesity, that was due to a series of skillful lies and a bit of scientific fraud.

The first was Ancel Keys who did a study that showed saturated fats (from meat, eggs) were protective but pretended it said they shortened people lives with heart disease

Then there was "research" from Kelloggs and Sanitarium that said grain was good for you

Then there was Coca Cola "research" that said sugar was good

Then there were three Seventh Day Adventists who got positions of power and said meat was bad, vegetarianism good (because meat causes masturbation)

So people increased their sugar, increased their vegetable oil, increased processed food, reduced meat and got fat, or if naturally thin, just got unhealthy

It turns out our only healthy diet is low carbohydrate. A little bread, some veg, a good amount of meat