Allergic reactions to ingredients in the foods you eat can range from mild to severe; they can even be life-threatening in some cases. But not every reaction to food is an allergic reaction. Some people just have trouble tolerating certain foods. For instance, my daughter can't tolerate parmesan cheese. If she eats more than a sprinkle, she has nausea and diarrhea.

Of course, if you are sensitive to food in any way, you'll want to avoid eating it. But it is especially important to identify...