I think it's loss of food culture too, which is where anecdotal evidence of someone's grandad or great grandma's diet from over half a century ago can provide useful information. Huge food manufacturers have stepped in to provide cheap, mass produced junk food whereas years ago that option wouldn't have existed. Also the loss of manual work in many deprived areas. I know, because that's where I grew up and is part of my heritage. My parents and grand parents generation had to cook family food from cheap ingredients, pies, hotpot, stews, organ meats like tripe or liver. My mum and her family were from a part of the country where fish, not cod but less desirable fish, and shellfish were a staple food source, probably with a side order of chips also! Obviously though, theres a difference nutritionally between old style handchipped fresh potatoes fried in beef fat or lard and what you have now. There was no iceland, aldi, or suchlike but what there would have is a regional food culture, that has largely disappeared in deprived areas.
My OH is forrin born, and I know if we live off his own food, the ingredients of which we can largely source from ethnic stores, our shopping bill would be very cheap. We would eat some meat, not loads, beans, lots of starchy filling food which stretches well. That's his own food culture, and he has said himself, from the developing country he is from, even the poorest people can eat something, something healthy. That's because they have a strong food culture which is based on eating locally sourced food and meats which are just not desirable over here, utilising the whole of the animal not just a chicken breast or steak or muscle meat. And the poorest will still have that knowledge of what is healthy and good for their bodies. But they wouldn't be fat!