My step mum got to 97 with no diabetes and a maintained an average weight
I think for most of her life she was pretty strict about 3 proper meals a day (mostly meat or fish and 2 or 3 veg), no snacking . She would allow 1 biscuit with a coffee, never cake except birthdays. Fairly little prepared stuff.. cooked most from scratch. it was just continuing habits from her childhood and wartime and she never fell into convenience food habits .Fruit was only when seasonal and cheap. Exotic meant rare and expensive, not peaches or strawberres all year round.
She brought up 3 boys who are all slim and nondiabetic and now in 70s.
When I look back I think those "old fashioned ways" might have been right.
No nuggets or chips in oils, little processed foods, it was OK to be hungry until next meal time etc
Today advertising and marketing sells us food they want us to buy, supermarkets don't provide just what we need and no more, they are continually pushing more into us.
Sorry.. went off on a rant...!