There was a comedian, Lewis Black, on HBO who said, to the effect, that on ones knows what a ‘good’ diet is. What you eat might kill the person sitting next to you.
I am inclined to agree with that thinking because it all boils down to genes, both good and bad genes.
My first father-in-law would put beef gravy on his pie. He ate anything and stayed slim until his untimely death at 92. My dear Mother ate anything she wanted, tried every diet known to man, was over weight her whole life and had to just decide she was tired of living, to die at 92.