I agree, the author made this up, and definitely not describing my grandparents. They bought their food from the supermarket, and boxed goods such as cereals, cake mixes, Hamburger Helper, etc., had preservatives, lots of salt, and artificial dyes. They liked TV dinners and my grandfather who lived well into his 90s, smoked a pack a day! They used real butter and whipped cream, as well as much fattier meat than we use now. (I can remember when the FDA changed the grading of meat, and the lower leaner grades became Grade A. The Grade A meat of my youth is now Kobe type beef.)
All but one of my grandparents all lived to ripe old ages and the grandfather who died young probably succumbed to injuries from exposure WW-I mustard gas.
My grandparents all born in the 1890s!
By the way, one of my aunts, born in the 1920s, did have a lot of food allergies as a child.
It’s like modern old wive’s tales.