Investigate every ethnic cuisine you can and every novel foodstuff you can find.
I’ve suffered from multiple food allergies pretty much all my life (and I’m pushing 50). My alternatives were either a highly restricted, boring diet or seeking what was out there that I could eat.
Also, please tell me he’s under the care of an actual allergist.
Desensitization treatment for anything for which it applies - getting five years of four allergy shots a week wasn’t all sunshine and puppy dogs but it was of immense help and I’d do it again in a heartbeat if there was any more benefit to be had. This should be done ONLY under the strict supervision of a professional allergist.
Anyhow - back to food. Yes, that list is a pain in the butt, but let’s look at broad categories:
Forbidden grains: corn, wheat.
OK - can he eat barley, rye (but check carefully for it being mixed with wheat or corn), oats, rice, millet sorghum, buckwheat/soba, teff, and/or quinoa?
Forbidden nuts/legumes: peanut, tree nut, soy.
OK - can he eat lentils, peas, sunflower seeds, snap (green) beans, kidney beans, red beans, pinto beans, black beans, mung beans, adzuki beans, chickpeas…? There are actually a LOT of beans out there. He may not be allergic to all of them but, again, determining this must be done carefully and please discuss it with his doctor. I know that some docs find it easy to simply say “avoid everything in this category” but when you get into multiple allergies some fine tuning is required.
For myself, peanuts, lentils, and green peas are strictly off limits. So I use almond butter in place of peanut butter, as an example which, of course, won’t work for your nephew since he can’t have either, but it’s an illustration of substitution. If he can’t have pinto beans but he can have black beans then made refried beans with black beans instead of pintos and make your tacos out of teff instead of corn or wheat (teff is an Ethiopian grain often cooked into a tortilla-like flatbread called injera).
You can’t always make such substitutions but it’s worth investigating. And you will be making substitutions!
Forbidden dairy - is it JUST cow’s milk, or ALL forms of milk? If it’s JUST cow then goat’s milk, cheese make from goat or sheep milk, and so on might be viable alternatives. If not - humans do not require milk past weaning. He can live without it. He may be enjoying Italian ice and sorbet in the summer instead of ice cream (and do be careful what’s in those) but elimination of dairy is OK from a nutritional standpoint.
As a note: my niece is highly allergic to all forms of milk. She makes her own sorbet. (she can’t have soy, either, so tofu ice cream substitutes are off limits to her)
Forbidden meats: chicken, pork, egg
OK, what about beef, venison, buffalo, turkey, quail? Can he eat fish? If the answer is yes, then all the varieties of fish and seafood are open to him. If he can’t… sigh. It’s important to determine this for this rather than going by “well, he’s so allergic we just assume he can’t eat fish…” If he CAN eat seafood then you might be able to substitute some types of fish sauce (check the ingredients) for soy for Asian style cooking at home.
If he’s allergic to chicken then it makes sense he’s also allergic to eggs - but are non-chicken eggs OK? Could he eat, for example, duck or quail eggs? These would be harder to obtain, but might be safe for him to eat. Does he live somewhere that his family could keep a couple of egg-laying ducks around for him?
In his case, stay away from the meat substitutes tofu (soybean) and seitan (wheat).
Forbidden fruit: banana, avocado, pineapple.
OK, what about oranges, grapefruit, grapes, kiwi, lychee, plums, peaches, cherries, berries, apples, pears, papaya, dragonfruit, nopoles (prickly pear), mangoes, ugli fruit, persimmons, apricots, figs, dates, melons… there are a LOT of different types of fruit out there.
Avoid plantains - they’re basically a type of cooking banana.
Forbidden vegetables: sweet potato.
Is that all? Really? There’s the broccoli family, the cabbage family, turnips, beets, chard, carrots, spinach, onion/garlic/leeks, the lettuce family, potatoes, tomatoes, the pepper families, the squash family… there are a LOT of vegetables out there.
Forbidden spices and condiments: vanilla, cinnamon, coffee
Alright, that’s a pain in the butt, but you can live without all of those.
More advice:
Get used to cooking from scratch from raw ingredients. The upside is that he’ll probably wind up healthier in the long run from all this.
Teach him how to cook EARLY. Age 4 is early enough for him to start helping, learning about measurements, what things look like, and watch preparation of food. As he grows older teach him to use the microwave and, as appropriate, how to prep and cook food in multiple ways. He’ll also need to learn how to “decontaminate” utensils to remove possible contamination.
Teach how to say NO and make it stick. the world will not reliably provide an allergen free bubble. He WILL encounter people who, through either ignorance or malice, try to get him to eat stuff that, for him, is poison. He needs to be able to say NO to an adult trying to force food on him. His parents and extended family needs to back him up. He may need to fend off siblings, cousins, and other relatives. He will definitely need to be inoculated against peer pressure.
Other random thoughts:
If he can eat olives, GREAT - olive oil can frequently be substituted for butter, especially on vegetables. Microwaving vegetables with some olive oil on top can be a great, easy intro to cooking and healthy eating. It can also be used for pan-frying and as a general cooking oil.
If he can tolerate sesame seeds then tahini can be used as a sauce (but watch the ingredient list, as always).
There are a lot of condiments and spices that don’t require either vanilla or cinnamon.
There are other things to drink besides coffee (tea is my favorite)
Can he eat sea vegetables? That’s kelp and seaweed, which may sound off putting but can be quite tasty. The Japanese use kombu (a type of kelp) to make a traditional broth called dashi that serves a similar purpose to chicken broth in American cooking. While it also frequently incorporates things like bonito (which is fish, which may or may not be on his forbidden list) you can make it with just water and kombu, and it’s about as difficult as brewing tea. Actually, the hardest part for me was finding a source of kombu, what with being 2000 miles from any ocean.
Can he eat mushrooms? Aside from the traditional uses of mushrooms in Western cuisine, *dashi *made with shiitake mushrooms as well as kombu is a bit more tasty than kombu alone.
Sushi! If he can eat fish, great, if he can’t eat fish then strictly vegetarian/vegan maki rolls could work. All you need are sheets of nori, rice, and vegetables. Just be careful what is mixed in with the rice.
Get a food processor, a crock pot, and a rice cooker Very useful, all of them.
The biggest problem I see with his list is finding a reliable source of protein for the kid, but as I’ve noted, that needs to be done with the help of a professional and not some allergic layperson on a message board.
Good luck - I know it’s overwhelming, but try to focus on what he can eat rather than what he can’t.
.Sucks, and most annoying is the unpredictability of an attack and severity.
or the stable goats they kept for company for a couple of the twitchier horses.]