Scot M. Lewey, DO, FACG, FASGE, AGAF
Clinical Professor of Medicine
Food allergies result from specific immunoglobulin (Ig) known as IgE antibodies. These IgE antibodies are
made as an adaptive defense response by the body. A particular food protein acts as an antigen or foreign
protein that the body mistakenly believes is threatening to invade the body. Food proteins are then allergens.
These food allergens can cause IgE mediated allergic reactions whenever these foods are eaten.
Symptoms of food allergy are caused by food specific IgE antibodies triggering mast cells, basophils and/or
eosinophils residing in the skin, nose, throat, lungs and digestive tract to release histamine and other chemical
mediators that initiate an acute inflammatory reaction in those tissues. The results are the allergic symptoms of
hives, swelling and itching of the skin, nose and mouth, wheezing or difficulty breathing. Less commonly,
problems swallowing, nausea, vomiting, abdominal pain and diarrhea, occur. If the food allergy is severe or the
exposure large, collapse, shock and death can occur if the reaction is not immediately reversed.
Food allergy testing consists of testing for the presence of specific IgE antibodies to foods or histamine release
in the skin in response to a food. RAST or the radioimmunosorbent assay test looks for presence of elevated
food specific IgE antibodies in the blood. Skin testing for food allergy consists of applying extract to pricked skin
or injecting small amounts of the extract under the skin. Histamine is used as a control. The test is considered
positive if a hive occurs as large as or larger than the histamine control. The larger the reaction the more likely
a significant food allergy exists. Questionable reactions on skin prick or scratch test are usually followed by an
intra-dermal skin test. In contrast to pollen allergy, food allergy skin testing may be less reliable.
The most common food allergens are peanut, cow’s milk, wheat, corn, soy, shellfish, eggs, and tree nuts.
Food allergy is treated by avoidance of known food allergens. Those foods are then simply avoided.
Desensitization to foods is not very effective like it is for pollen allergy.
No, though food allergies are an adverse reaction that could be considered a form of food intolerance or
sensitivity these terms are usually reserved to describe other adverse food reactions that are not allergic in
nature. Also, though food intolerance and food sensitivity are often used interchangeably they can distinguish
different types of adverse food reactions.
Food reactions that are not allergic in cause may have a variety of causes. Causes include intolerance due to
inadequate digestion. The most common and well-known food intolerance is lactose intolerance that is due to
lactase enzyme deficiency.
Other sugar enzyme deficiencies can occur less commonly. More commonly, excess sugar load overwhelms the
intestinal enzymes resulting in incomplete digestion of the sugar followed by bacterial fermentation producing
excess gas, bloating and diarrhea. The classic example is fructose maldigestion causing these symptoms in the
“Big Gulp” syndrome.
Other causes include poor food digestion, inadequate digestive enzyme secretion by the pancreas or impaired
enzyme activity from bacterial overgrowth. Some foods contain complex sugars known as oligosaccharides and
polysaccharides for which humans lack digestive enzymes. Examples of foods that may cause adverse
reactions by this mechanism include beans and certain vegetables like broccoli, cabbage and cauliflower.
Food proteins or protein carbohydrate complexes known as lectins can injure the small intestine and trigger
adverse immune reactions. Foods and food additives can also have a direct toxic effect on the gastrointestinal
tract that causes adverse food reactions labeled as sensitivity or intolerance.
Digestive enzymes for proteins, carbohydrates and fats are released by the pancreas and work best when
mixed with bile from the liver. Anything impairing pancreatic or liver function can result in an adverse food
reaction. Abnormal bacteria levels in the gut can impair digestion. Undigested food is fermented resulting in
abdominal pain, bloating, gas, and diarrhea.
Some foods and food additives have a direct toxic effect on the gastrointestinal tract. Additives such as MSG
and sulfites can cause symptoms, including flushing and diarrhea or the “Chinese restaurant” or “salad bar”
All foods contain proteins linked to carbohydrates known as lectins. Some are highly resistant to digestion or
are lethal in humans. Others are highly toxic to the humans unless the food is soaked and then cooked well. An
excellent example is inadequately soaked and cooked kidney beans. Kidney bean lectins will cause a food
poisoning like illness if the beans are not soaked a prolonged period and cooked thoroughly.
There are numerous symptoms commonly associated with food sensitivity. The symptoms can be both
gastrointestinal and outside the gut. They include digestive symptoms such bloating, gas, diarrhea (and
sometimes constipation), abdominal pain, nausea and vomiting. Non-digestive symptoms include severe
fatigue, headaches, joint and muscle pains, skin rashes, weight loss or gain, anemia or nutritional deficiencies,
irritability, depression, mental fogginess, and nerve pain (neuropathy). These symptoms may be misdiagnosed
or mislabeled as irritable bowel syndrome, chronic fatigue syndrome, reflux, ulcer, and fibromyalgia. Food
sensitivity is treated simply by elimination of the offending food.