The "gluten-free" phenomenon began with the autoimmune genetic disorder Celiac Disease. Someone who has celiac disease can not process or tolerate gliadin (a sub group of gluten, found in wheat, barley, and rye). In an attempt to help out our celiac friends the FDA began regulating "gluten-free foods", which should really be called "gliadin-free foods" or better yet "celiac-friendly foods". If you're still with me, this means that if you have an intolerance or allergy to gluten (not celiac) truly any plant in the grain family may cause a reaction for you. This is important because people who are trying to avoid gluten products tend to be very under educated about their choices; i.e. choosing gluten free bread, pasta, pancake, cake, cookies, etc; gluten-derived foods or gluten contaminated foods like vinegar, modified food starch, oats, grain alcohol, beer, soy sauce... does not mean it's healthy for you! The substitutes for wheat are typically white rice flour, potato starch, tapioca, sorghum, white corn (GMO!!), corn starch, etc. These are not health foods (i will make an exception for sorghum). If you notice a reaction when eating breads, grains, flours, etc you would be better off keeping that entire food group out of your diet than trying to find a net zero nutrient food to replace it. Make sense?
The difference between food allergies and food intolerances is really quite simple. A food intolerance is typically categorized as a lack of enzymes to break down the suspect food and thus this causes a reaction; bloating, gas, diarrhea, upset stomach, etc. Food intolerances are not typically taken seriously, as it's not an "allergy" so you can eat it sometimes right? That is not my understanding nor suggestion. Food intolerances can be just as serious as food allergies, and can even in most cases lead to a true food allergy should you ignore your bodies first signs of an intolerance. This one can be tough to test for. I run a saliva test in my office that tests for high levels of gut antibodies called IgA's. This is a useful tool in beginning to determine mine or my clients intolerances, however food elimination diets probably provide the best information surrounding your food intolerances.
A food allergy will cause an immediate response, i.e. you KNOW when you're allergic to a certain food. If you eat shell fish of any kind and immediately find your throat closing, air pathways restricted, break out in a rash, feel extremely itchy, etc...this is an allergic reaction. You most likely will let this happen twice before you never ever touch that food again. This makes true food allergy testing a waste of your time, unless you are completely oblivious to the obvious signs and symptoms of your own body.
Food allergy tests are typically done via blood, and probably won't tell you anything you don't already know. The other confusing part about allergy testing is (and if you've had one done you know what I'm talking about) you may show a positive response (via high IgG antibodies) in your blood, but it doesn't mean your reacting to it just because your antibodies are high. Yup, that basically means these tests can or can not help you. You could have a lot of positive antibodies for kiwis, but when you eat kiwis...nothing happens! This can be conflicting evidence and extremely confusing, you think "so now what, do I avoid kiwis?" My suggestion would always be to listen to your body! Testing can be a useful tool but it is not the end all answer to what's going on in that complicated body of yours.
My Substitute List:
Wheat = brown rice or millet or sweet potato
Cows Milk = Almond milk
Eggs = small chicken breast, smoked salmon, ground turkey, etc
2 tbsp flaxseed, 1/3 c water (baking substitute)
Soy = just avoid all together
Carbohydrates in general = veggies, veggies, veggies
Your best bet is to eat clean. Eating clean means eating plants, fruit, organic healthy animal protein, eggs, nuts & seeds, and good ol' H2O...that's it. Get your grains out or to a minimum, and make your plates more lively!