Nah, what changed is preponderance of highly processed junk food.

When I lived, in my childhood, in communistic Bulgaria/Czechoslovakia, nobody was starving. Yes, we did not have bananas and Argentinian steaks, but there was enough basic food, including the protein-rich one (eggs, cheese, even meat, although the best cuts were 'under the counter'). Still, few people were really obese; those were obviously sick.

Nowadays, there is plenty of junk food. The food is not really cheap (especially with the recent inflation), even the junk one. Still, being obese is (almost) the new normal. You can see that everywhere.

Yes, people spend more time indoors - but even in the old times people tended to spend a lot of time behind TV.

My hypothesis is that the junk food just does not have enough real nutrients, just mostly empty calories. So the body signals 'I need more nutrients', to which the typical response is 'here you have more empty calories'.