The incidence of food allergies has increased in the last 15 years. This may have resulted from a variety of factors: increased stresses on the immune system (due to increased pollutants in the air, water and food); earlier weaning and introduction of solid foods to infants; genetic manipulation of plants resulting in foods which have a greater chance of cross reacting with normal tissue.
Food allergies have a well documented genetic predisposition. In households where both parents are allergic, 67%of the offspring are allergic. Where one parent is allergic, 33% are allergic. Food sensitive people have been observed to have unusually low levels of IgA. It has been suggested that a transient IgA deficiency may predispose to the development of food sensitivities in the first few months of life. It is interesting to also note the correlation of stress levels to impaired IgA secretion. This may explain the relationship reported by many sources between food allergies and severe mental stress. Foods may produce allergic reactions by a variety of methods. Immunologically produced food reactions result from the reaction of the food substance with sensitized IgE antibodies located on circulating mast cells. This leads to immediate hypersensitivity, so called because most of the symptoms develop within 30 to 90 minutes of ingesting the offending food. These symptoms include the well known anaphylaxis symptoms of allergy; bronchiole congestion and asthma, hives and eczema, headaches, loss of memory and "spaciness."
The cytoxic or tissue destructive reaction results from the activation of complement. This reaction results in destruction of the cell in which the food allergen is bound. Up to 75% of all allergies are accompanied by a cytoxic reaction.
Immune complex related reactions result from further immune stimulation by the circulating immune complex of antibody and allergen. Normally taken up by the liver, these can enter the general circulation and stimulate tissue injury by immune reaction or deposition of immune complexes in delicate tissues and organs. Improper digestion, a repetitive diet and a lack of integrity of the intestinal membranes all predispose to the development and maintenance of food allergies.
It has been well documented that partially digested dietary protein can cross the intestinal barrier and be absorbed into the bloodstream. This causes allergic reactions at the site of transfer or at other distant sites, or systemically. Factors which influence intestinal absorption of macromolecules include immaturity of the GI system, abnormal intestinal flora, vitamin A deficiency, decreased gastric acid secretion, pancreatic insufficiency, mucosal ulceration or inflammation and diarrhea.
Symptoms and diseases commonly associated with food allergies would include such diverse problems as low back pain, bed wetting, chronic bladder infections, canker sores, middle ear infections, asthma, acne, headache and duodenal ulcers. Some of the common physical signs of allergy are dark circles under the eyes; puffiness under the eyes; horizontal creases in the lower eyelid; chronic swollen glands and chronic noncyclic fluid retention. Hyperactivity in children has been speculated to have its cause in food intolerance.