Food sensitivities can be a problem; they are a problem on two fronts. First, is the problems they create in your body. If one looks up the symptoms that can be attributed to food sensitivities, the symptoms can cover just about every one in the book; everything from nasal allergies, headaches, and blurry vision to frequent urinary tract infections, abdominal pain, and fatigue can, in the right persons, manifest because of what they eat.
The second problem food sensitivities pose is diagnosing them and pinning down what foods are causing a problem. It is a rare occurrence for a single food to be causing all the health problems one might have. It is not as uncommon for multiple foods to be causing one's impaired health. There is a general rule of thumb that the foods you are reacting to are paradoxically the foods you consume most; but even that isn't of much use. The most effective test for food allergies/sensitivities is the elimination-challenge diet. This diet removes the suspicious foods for a period of 2-4 weeks, and then methodically re-introduces one food at a time watching for the reactions to return. It is extremely effective - if you eliminate all the offending foods. The trouble is how do you know just what all to eliminate? Also, eliminating your favorite foods for weeks is an intense challenge when the list was made up largely as a guess - "Well, maybe this is a problem?"