Many people associate food allergies with substances that make them feel sick. And because feeling ill can be linked with sugar indulgences or binges, some often claim an allergic reaction to the sweet stuff. But as the American Academy of Family Physicians reports, “a condition is called a food allergy when the immune system (the part of the body that fights infections) thinks a certain protein in a food is a 'foreign' agent and fights against it. This doesn't happen with sugars and fats.” So that uncomfortable feeling you may experience after consuming sugar might be a food sensitivity, but it is not an allergic reaction.