Restricted diet strategies
Everyone seems to have some sort of diet issue these days. Whether you're avoiding gluten, nuts, dairy, or anything else, here's what I've learned from over 20 years as a vegetarian (2 of them vegan).
You can eat very well as long as you cook. This includes entertaining well (unless a guest's food issues are the polar opposite of yours).
Processed foods contain really weird ingredients. Organic products have fewer additives, but never assume. Learn to read ingredient lists, look up anything you don't know, and spot-check even "safe" items periodically since they don't always advertise formula changes.
Reproducing current favorites with alternate ingredients is rarely the best approach. Finding new cuisines and dishes which can become favorites is much easier and usually tastes better.
The internet has a recipe for just about everything. Sometimes when people adapt for one food issue, they get weird in other ways, like ditching chocolate in favor of carob or thinking vegan cheese is a food. More often than not, I find a promising "normal" recipe—or several examples—and make my own substitutions. The other strategy that works really well is to start with a couple ingredients and see what pops up. I did that yesterday with "quinoa yogurt recipe" and "yogurt cilantro recipe," and have a few new recipes to try.
When substituting ingredients, the best fit often varies. For example, cane sugar may be best replaced by honey or rice syrup in an Asian main dish, but for baking you may prefer date sugar. When thickening a soup or sauce, I may reach for cornmeal, wheat flour, potato starch, or corn starch. My most common milk replacement is So Delicious unsweetened coconut milk (dairy case) but I also use soy milk and regular coconut milk at times.
Flavor is easy; chemistry is hard. Casseroles and soups are wonderfully tolerant of substitutions. Baked goods which rise can be incredibly fussy (try flatbreads or cookies instead). Likewise anything which "sets" like a custard can take a lot of experimentation or exotic ingredients.
Find some quick recipes or cook in volume and freeze individual servings. It keeps you from missing prepared foods and is generally better quality. A few on my 5-30 minute list are corn grits (sweet & savory possibilities), tacos with instant refried beans, sushi rice with edamame & nori, miso soup, pakora/falafel variants, etc. I also make my own beans, and freeze in 14oz containers so I can grab one in place of a can. (Holler if you want specific recipes.)
Restaurants are problematic. I'm really diligent about interrogating waiters and know what to ask for most cuisines, and meals still occasionally contain unsanctioned ingredients—by design or contamination. This means it's always a little (or a lot) stressful when I'm not in an all-veggie restaurant, so if you have allergies you may want to avoid them entirely. Likewise eating at a friend's house is difficult, though in this age of food issues you may have some folks who can (and would like to!) accommodate your diet. "Pre-eating" is a valuable strategy, and traveling involves packing lots of snacks and sometimes compromising your diet.
Bulk bins are fabulous for getting grains, legumes, and spices, especially when you just want a taste. Try Whole Foods, co-ops, and other natural or yuppie markets. Bob's Red Mill and Amazon are also useful resources.
Radical diet changes sometimes call for new gear. I love my rice cooker, which does a great job on quinoa and even has a special sushi rice button. If you find yourself making something new a lot, it may be time to shop.