Definition. True food allergies occur in people who make allergic antibodies against a protein in food; symptoms include itching in the mouth while eating it, nausea, vomiting, diarrhea, hives, and anaphylaxis in highly sensitive people. Most of the reactions that people call "allergic", such as headaches with msg and nasal congestion after drinking red wine, aren't.
Complicated ans. There does seem to be more recognition and discussion about food allergy. These is probably due to two factors: one we are able to more accurately diagnosis food allergy and two food allergy is perceived to be more prevalent than it actually is. The perception is that 20% of the population is food allergic, good epidemiology suggests that number is much lower around 4-6% or so dep upon pop.