There are few food allergens that cause antigen/antibody reactions - shellfish and peanuts are perhaps the best known, indeed some food intolerance sufferers have no classical allergies and for this reason may never suspect that their arthritis, migraine or panic attacks are caused by an unusual reaction to common foods. People allergic to the same food may have entirely different symptoms, just as people with the same symptoms may be allergic to quite different foods.
Symptoms of food intolerance can be surprisingly varied. Catarrh, digestive and stomach trouble, backache, swollen glands, depression, anxiety attacks and phobias, palpitations, irritability, headaches, mouth ulcers, aching joints and muscles, childhood hyperactivity are all possible, as well as more serious conditions. Because onset of symptoms are often delayed, they seem to bear no relationship to diet at all, so it is not-surprising that many allergic people have had a variety of tests, diagnoses and treatments, and are often told they are suffering from stress, hypochondria or 'nerves'.
Many food 'allergies' are masked, that is they seem to be more like addictions as the sufferer may have withdrawal symptoms if the food is not eaten, but there are a number of symptoms that commonly point to food intolerance - persistent tiredness, not helped by rest; over- or underweight or fluctuating weight; occasional palpitations after food; occasional excessive sweating, unrelated to exercises; occasional swelling or bloating of hands, face, ankles or abdomen.
One should always suspect foods that one craves as being a problem. How often does one hear "I can't get going in the morning until I've had my orange juice". "I've got to hava a cup of coffee mid-morning to keep me going"