Food Intolerances or Sensitivities
Foods or food components that elicit an adverse reaction but have no established immunologic mechanism are termed food sensitivities (recommended or preferred term in the United States or food intolerance. Among the mechanisms for different forms of food sensitivity are food toxicity, as well as pharmacological, metabolic, physiological and psychological food sensitivities. Those with no established mechanism are "idiosyncratic" food sensitivities.Table 1 summarizes the major categories of food sensitivities.
Food toxicity results from microbial contamination of food causing GI symptoms generally from preformed toxins, such as staphylococcal enterotoxin, or replication of enteric pathogens, such as Shigella, Salmonella, Campylobacter or Escherichia coli. These reactions usually do not recur and have typical presentations.
Pharmacological food sensitivities are reactions to food due to chemical components in foods and food additives, and most cause symptoms outside of the GI tract. Examples include histamine found in Swiss cheese, tuna, and other scombroid fish, causing headaches and diffuse erythema of the skin, and glutamate, which can cause a syndrome of warm sensation, chest tightness, headache, and gastric discomfort.
Among the metabolic food sensitivities, the most common is lactose intolerance. Primary lactose intolerance is most commonly due to declining levels of intestinal lactase activity in later childhood and adulthood, but can rarely manifest as a congenital deficiency. Symptoms are dose dependent and include bloating, flatulence, and diarrhea. Secondary lactase deficiency can also be seen in viral gastroenteritis, radiation enteritis, Crohn's disease, and celiac disease among others.
Physiologic food sensitivities result from physiological reactions to food components or additives. An example is the starch found in legumes, which serves as a substrate for gas production by colonic flora. Psychological food sensitivities include taste aversion, texture aversion, fear of the consequences of eating, conditioned responses, eating disorders, and those secondary to a traumatic experience ( e.g., from abuse), neglect, or food poisoning. Idiosyncratic food sensitivities have no established mechanism and are, in general, controversial. Among the most common food proteins that have been reported to cause idiosyncratic food sensitivities are gluten and cow's milk.