Food allergies are due to IgE antibodies made for specific foods that an individual has for some reason developed because their body has misinterpreted the food(s) as a foreign invading protein. The presence of IgE antibody to the specific food a person is allergic to results in an immediate immune reaction of the body to the food when it is eaten. The IgE antibody binds its specific food protein and initiates reactions in the body that include the release of chemicals such as histamine that may result in symptoms of itching, swelling, wheezing or difficulty breathing, rash or hives, and if severe, shock resulting in death if not reversed. Vomiting and diarrhea may occur but are less common.
Testing for the presence of allergy to a food or foods can be done by blood test or skin testing or both. One of the most common blood tests is the RAST test that looks for the presence of the specific IgE antibodies to common food allergens and other foods based on a history suggesting that a particular food is suspect Bottled and jarred packaged goods. Skin testing is done by injecting or applying extracts of the common and any suspect food(s) to pricked or scratched skin and looking for diagnostic “hive” like reactions at the site of the suspect food. The most common food allergens are peanut, cow’s milk, wheat, corn, soy, shellfish, eggs, tree nuts, chocolate, pork, tomato, and citrus.
The terms food intolerance and sensitivity are commonly used interchangeably. They refer to a group of food reactions that occur that are not IgE antibody caused. In more general terms they refer to any adverse or unpleasant reaction that occurs after a food is eaten.
Food reactions that are not allergic in cause may have a variety of causes. A particular food may not be tolerated because it is not digested adequately due to an enzyme deficiency. Lactase, the enzyme that digests milk sugar or lactose, is present on the surface of the intestine lining cells. Lactase deficiency can be inherited or acquired. It commonly occurs whenever the intestine lining is damaged. Because the lactase enzymes are on the outer most surface of the intestine they are more vulnerable to injury. For example, after intestinal flu or in untreated Celiac disease, lactose intolerance is common. Other sugar enzymes can be deficient or the intestine can be simply overwhelmed by too large a sugar load at one time. A classic example is “the Big Gulp” syndrome when someone drinks a giant cola beverage then experiences the “gut ache” from the tremendous amount of fructose. Large amounts cannot be handled by the intestine and that results in bloating, urgency and terrible diarrhea.
Deficiency of digestive enzymes released into the intestine can result in poor digestion of foods. For example, when the pancreas gland is damaged (pancreatitis) chronically, usually from chronic alcohol abuse, or is congenitally underdeveloped or malfunctioning (e.g. cystic fibrosis). The pancreatic enzyme deficiency that occurs results in malabsorption, especially for fats, that cause symptoms of diarrhea and weight loss. Abnormal bacteria types and levels in the gut, also known as dysbiosis, and abnormal excess levels of “bad” bacteria or presence of bacteria in upper small intestine where little or no bacteria normally occur (bacterial overgrowth) can interfere with digestion, absorption or cause fermentation of food resulting in symptoms of 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” syndromes.
All foods contain proteins known as lectins. Some of these proteins are highly resistant to digestion and are toxic to the human intestine especially if they are not pre-treated by soaking, cooking well, or removing toxic portions. For example, inadequately soaked and cooked kidney beans will cause a food poisoning like illness. There are several foods that have lectins that are poorly tolerated by many humans and are lethal to insects and pests. One researcher, Loren Cordain PhD., author of the Paleo Diet, has published extensive research on how the human intestine is not “evolved” to tolerate many of the foods we now eat but did not eat in the ancient “hunter-gatherer” times resulting in many of the illness seen in modern societies and the rising epidemic of autoimmune diseases. Several of the “modern” foods that were not part of the ancient diet but constitute much our diet now have well recognized toxic or poorly tolerated proteins known as lectins. Examples include wheat germ agglutinin (WGA), casein (cow’s milk protein), peanut agglutinin (PNA), soyabean agglutinin (SBA) and tomato lectin (TL) that have been shown in animal studies to be toxic to the human gut. There are a few published studies and little active research on the role of dietary lectins in health and disease.