While you're eliminating, start keeping a food and symptom diary. This will give you a place to record both what you ate and how it made you feel. Record any symptoms and cravings you're experiencing, too. Write down what time you ate or drank, and what you ate or drank. Record the time symptoms occur, and watch for trends. Does your mouth itch every time you eat an eggplant? (You might be sensitive to nightshades.) Do you break out in hives whenever you drink chamomile tea? (The herb is in the ragweed family.) This exercise will help you identify your triggers and link them to reactions, and it will give you a baseline to look back on when you reintroduce the food.
Choose the food you want to test and eat it frequently over the course of two days. If you're testing nuts, have peanut butter on rice cakes for breakfast, walnut milk for lunch, a handful of almonds for a snack, and maybe a cashew curry for dinner. Then keep an eye on your responses for the next day or two. Watch head-to-toe for any kind of negative reaction—headaches, allergies or stuffy sinuses, scratchy throat, heartburn, wheezing, GI complaints, diarrhea and/or constipation, skin rashes, fatigue, increased depression, confusion, or anxiety. All of these might be caused by, or exacerbated by, food allergies or sensitivities. Take copious notes.
More: 5 Foods That Make Your Pain Feel Worse
If by the end of the third day you have logged no response, the food is probably okay for you. If you've noticed a small response but you're not sure if it's coincidental, wait a few more days then reintroduce the food. It should be clear whether or not it causes a reaction. Refer to your diary to compare notes.
If you find you are having a reaction, you also have a cure: elimination. The best way to treat a food allergy or sensitivity is with avoidance. This used to be the only way. However, over the past few years, allergists have pioneered a technique called sublingual desensitization, in which the specialist administers minute but ever-increasing doses of the food you're reactive to, and over time, allergies and sensitivities decrease. Talk to your doctor about whether the treatment is an option for you.