My grandparents lived to 93 & 97, I believe in large part because Grandma cooked from scratch at every meal. A meat. A vegetable. A salad. And usually potatoes. But if a potato is the worst thing in your diet, you're probably doing all right.
Some relatives (well-educated people who should understand science better than most) have embraced a hard-core, plant-only, no-oils, no-fats form of eating based on the work of some cardiologist. I keep getting their 'just watch this...' links about the evils of fats & meat. They boil a lot. And -- having always had slender builds -- they now look emaciated.
The vegan relatives bought me some non-stick pans "so you can cook without oil." Did they think I was deep-frying in Crisco every night?!
Seriously, I keep waiting for their hair to fall out and their skin to flake off...