My great-grandfather ate white bread regularly from before 1910 and stayed thin all the way into his 90's. He spent his last ten years or so living with my family starting about when I was in middle school, so I remember it well. AFIK, he'd been eating the same kinds of stuff for 50 years -- cornflakes and whole milk for breakfast, sandwiches for lunch and meat and potatoes with a few veggies for dinner.

Especially when looking at my own ancestors (all of whom were thinner than me 3 generations back), I tend to discount any sort of "oh they were just genetic freaks" kinds of arguments. None of them really dieted or deprived themselves, but they were used to pretty bland monotonous diets. I clearly remember ordering pizza in high school and they tried eating it with forks and knives and said they weren't big on "Italian food". The truth is it's the more recent generations who are the freaks. We're used to access to pretty much any kind of tasty, convenient food whenever we want it.