Yes, if they had bad eating habits then even back in the day they died. But "fat" isn't a "natural" state. Even primitive people, if they are on their native diet, they don't usually get fat. It's when they change to a more modern diet they start having obesity problems.
WHO | Pacific islanders pay heavy price for abandoning traditional diet
https://dash.harvard.edu/bitstream/handle/1/11940214/McCoy_2012.pdf?sequence=1&isAllowed=y
Our modern dietary guidelines are what's making people fat. The Standard American Diet, as prescribed by the USDA, is responsible for our upsurge in Diabetes and Heart disease. Cooking with seed oils, like corn oil and soy oil, instead of olive oil, is a big part of the problem, because they are full of omega 6. Soy oil is in almost all bakery products, and almost every processed food.
That USDA food pyramid isn't based on sound science, it was developed by the food industry to sell products.
And Jillian Michaels is totally wrong. weight loss isn't just a matter of "calories in, calories out", and it doesn't matter where those calories come from. It actually matters a great deal. All calories are not "equal". I eat way more than the normal amount of calories; but I eat the right kind of calories.
OK, rant over.