|Before modern times, I suspect that many babies with severe food allergies simply wouldn't have survived. If a baby is allergic to some staple in the diet, he or she would probably be very sickly in early infancy (from the allergen in breastmilk) and then grow slowly, if at all, and then succumb to a minor illness- if they didn't die from anaphylactic reactions to allergens. I don't know if they were always able to specify what was wrong with "sickly babies" who died young.
I have a story about this. My dh was born/raised in India. He had feeding difficulties starting at a very young age. My MIL had some milk prodoction problems (she has hormone problems) and we are not sure which came first-- dh's refusal to suckle or her milk drying up. But in any case my dh refused to nurse on bottle or breast from 2 to 10 months old. My MIL fed him with a little medicine cup made for babies and that's what he survived on. She had to feed him drop by drop and a lot would be spit out or vomited out. This was baby formula that was available at the time. At 10 months he finally accepted bottles again after lots of trial and error, and he stayed on bottles for four years. Was a very picky eater, very thin kid and not very healthy.
My SIL (dh's sister) was born and MIL lost her milk at 2 weeks posptartum. SIL was a good eater but she just lost her milk. She had to start giving bottles. They brought a cow from the village and milked it and boiled it and that's what SIL was given. She was started on solids very early, with curd rice mixed with some dahl. At 4 years old she was found to have high eosinophils in her blood and she had asthma and food allergies. She is better now as an adult, seems to have mostly outgrown all but shrimp allergy.
My MIL said that traditionally babies in India are weaned no later than a year old, started on solids at around 4-6 months. My SIL just had a baby last July and she also had milk production and nursing problems and the baby ended up on bottles after awhile. They weaned the baby of formula at 6 months and put him on cow's milk and soft foods like those mentioned above. My MIL said that in rural India people nurse a lot longer and wean at around age 2, but that modern women wean earlier. We got into an argument because she doesn't think breast milk has any value after 6 months.
Mothers in India traditionally are put on a bland, iron-rich diet after the birth and for a few months.
As far as allergies go, both my dh and SIL had/have them and my second daughter also has severe food allergies. I feel that dh might have been allergic to things in his mom's milk just as my baby was with mine. As far as traditional values-- most cultures I know of do not restrict infants from trying foods. India may have been influenced by the west in some of its values or perhaps they always fed the babies foods early on. I know that in Hindu tradition there is a "first foods" ceremony that is done at around 4 months old where the baby is given something sweet to eat, usually sweet rice, so that their life will be sweet. After that ceremony they are fed solid foods regularly.