I'm gluten intolerant so presumably would have felt awful on my great granny's diet, as it presumably involved a lot of bread.
Can confirm, was absolutely awful even on a 70s diet, especially with issues with dairy, too. My mother didn't believe the 'stupid doctors' saying cutting out wheat and milk might stop my stomach pain, digestive issues, allergic reactions, inability to breathe through my nose, general weakness and daily headaches, never mind cross contamination and cross intolerances, along with a need to increase sodium intake to reduce fainting for what was eventually termed POTS. But at the same time, she banned me from having fizzy drinks, sweets and anything with artificial colouring in it because I 'went crazy on it'. Probably because I had some energy and didn't feel sick on the E numbers, sugar and citric acid.
Result - breakfast - single slice of homepride toast and margarine or cornflakes, shredded wheat, shreddies, readybrek, weetabix = start the day feeling sick. Easier not to eat at all.
Lunch - sweaty ham and salad cream sandwich, yoghurt, Club biscuit, juice carton. Or school dinners with all of the wheat = headache and feeling sick.
Tea - whatever I'd eat (which wasn't much, as if it didn't make me feel more ill than before, it was unflavoured, unseasoned and pretty miserable). I'd eat every vegetable, potatoes, rice, some fruit, chicken when available once a week, most fruit and nobody ever connected the fact that I felt so much better in summer with big salad plates of lettuce, tomatoes, cucumber, strong cheese, boiled eggs, celery, radishes, pickled beetroot and boiled potatoes - and stone fruits afterwards.
She never could reconcile that her 'faddy eater' would happily eat pulses, beans, anything spicy, vegetables that she'd never seen before (and wouldn't dream of going to buy because it was run by people who didn't look like her), pickles, seafood, fresh herbs, spices, smoked and preserved meat products (they tasted of something, thanks to the salt and smoke), gefiltefisch, sushi, stir fries, olives by the ton and nuts/seeds.