A few examples: coffee may cause burning in your stomach, rapid and/or irregular heart rate, and difficulty falling asleep. There adverse reactions are not due to a coffee allergy. They're due to the effects of caffeine, the stimulant drug present in coffee. If you drink too much coffee (or tea or cola or even eat too much chocolate), or if you are unusually sensitive to the effects of caffeine, you may experience these symptoms.
Gas, bloating, and diarrhea after eating milk or dairy is more commonly caused by lactose intolerance rather than a milk protein allergy. A decreased ability to digest lactose, the sugar found in all cow's milk (including low-fat and skim) is the cause of these symptoms.
Foods contaminated with bacteria may cause abdominal pain and vomiting. Food contaminated with hepatitis A virus may cause jaundice.
True food allergies cause problems in four parts of the body: the digestive tract, the skin, the respiratory tract (nose, throat, breathing tubes, and lungs) and the circulatory system (heart and blood vessels). Lagging reactions may involve digestion, breathing or the skin, but not the heart.
An elimination diet may be used to establish a relationship between a food you are eating and a symptom that you are having, regardless of whether that symptom is due to allergic or non-allergic causes.
You must completely eliminate the suspect food from your diet for at least ten days. Sometimes a food needs to be eliminated for a longer period of time - perhaps one to two months. Complete elimination means no cheating - not even a little - so you need to read labels. For example, if you are avoiding peanuts, you'll have to avoid foods that have "made in a plant where peanuts are processed" or there is any other mention of peanuts on the label.
If you are dramatically better after eliminating the food in question, then continue to avoid it. Consult with your physician before eating the food again as sudden re-introduction into the diet can sometimes trigger unexpected severe symptoms. If you experience no change by avoiding the food, you may safely add it back into your diet.