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A food allergy is an allergic reaction -- sometimes life threatening -- to certain foodstuffs. The eight most common food allergies in the U.S., known as the "big eight", are cow’s milk, egg, peanut, tree nuts, fish, shellfish, soy, and wheat.
Several woo meisters have claimed that food allergies are responsible for every malady a person can experience, from fatigue to impotence. Although fewer than 10% of the population actually have food allergies, as many as 30% of adults believe they have food allergies, and 50-90% of child "food allergies" reported by their parents aren't food allergies at all. This perception of more food allergy than actually exists feeds the all-too-common suspicion that, if you have any malady at all, it might be caused by a food allergy.
There is a certain amount of relation to gastronomic disorders and intolerances (such as lactose or fructose intolerance), but these conditions are not true 'allergies.' Rather than being autoimmune reactions, they are dysfunctions of digestion, such as lack of appropriate enzymes to break down some substances, or easily irritated GI tracts that respond badly to certain foodstuffs.
One highly dubious claim that's been repeated more than once is that, even if you have no allergic symptoms whatsoever, you might still have "hidden allergies" (usually to certain foods) that are causing all the problems in your life.
How do you tell if you have one of these "hidden allergies"? Why, take the special hidden allergy test provided by the woo peddler, of course! Or, if he doesn't offer testing services, perhaps he'll tell you not to take chances and just assume that all your problems are because you're allergic to corn, soybeans, tuna, peanuts, tree nuts, gluten, shellfish, bananas, household cleaners, bed linens, and air. And whatever it is placebo capsules are made out of.
On one episode of the Dr. Oz Show, he claimed that if you have a hidden allergy to a food item, you might have no symptoms whatsoever immediately after eating something you're secretly allergic to, and then three or four weeks later, pow, you start getting a whole bunch of unpleasant symptoms. He demonstrated this by pouring water on a piece of pink paper and setting off some small delayed-detonation pyrotechnics on his demo table, thereby proving beyond a shadow of a doubt that everything he was saying must be true.
- ELISA/ACT, like cytotoxic testing, looked at the reaction of the subject's lymphocytes in vitro to alleged allergens to find "hidden allergies." It operated under the false assumption that an immune response was synonymous with an allergy. The name is unfortunate, because ELISA is also the name of a legitimate test for certain infectious diseases, and the name of a class of protocols used in the process of discovering new pharmaceuticals by drug companies.
- The Mediator Release Test (MRT) is another test you'll only see promoted by "alternative" medicine vendors, like the LEAP program and some chiropractors. It tests your reaction levels to 250 foods by putting foodstuffs into samples of your blood and looking for immune cell responses. Several sites reference a "blinded peer reviewed scientific study" which showed MRT to have 94.5% sensitivity and 91.8% specificity. The study in question comes from the journal Przeglad Pediatryczny (1997, Supplement 1, pp. 61-65), published by the Polish Pediatric Association; this journal contains both original research and studies originally published elsewhere and is rather difficult for English speakers to track down. Even if the data are from a well-designed experiment with a large sample size, it might only mean that the test has a 90+% sensitivity and specificity to immune cell responses; how such responses correlate with actual food allergies or intolerances might not have been discussed at all.
- Tests for Immunoglobulin-G have become popular, but IgG is more an indicator of exposure to proteins, not of an allergic reaction to them.
- The ALCAT test has started becoming popular, especially among those claiming gluten sensitivity. Its efficacy, like so many other fad tests, isn't supported by research.
- Skin-prick tests are the preferred method used by real allergists to discover allergies. They work pretty well for detecting sensitivity to environmental allergens (e.g. pollen and dust mites), but can be of dubious merit where food allergies are concerned. They, and their cousin-German the CAP RAST blood test, are both very sensitive but not very specific. This means that there is a great danger of a false positive, particularly if the subject has other allergies.
Also known as food intolerance, or non-allergic food hypersensitivity. "Food sensitivity" is a catch-all term for a broad spectrum of reactions brought about by foodsuffs, whose only thing in common is that they're not food allergies.
Among the conditions that qualify as food sensitivities (but not food allergies) are:
- gluten intolerance (but not the Celiac disease that may underlie it)
- lactose intolerance
- fructose malabsorption
- salicylate sensitivity
Frustratingly, the symptoms for food intolerances tend to be very similar to the symptoms for food allergies. Hives, mouth ulcers, nausea, gas, diarrhea, and even (depending on the sensitivity in question) anaphylaxis. The main outward difference is the speed of the reaction: food allergies tend to kick in almost immediately upon exposure, but food intolerances can take anywhere from half an hour to 48 hours to show symptoms.
Because of its slow onset, it can be harder to determine the food that caused your sensitivity reaction. In this sense, and because food intolerance used to be called a "pseudo-allergic" reaction, a food sensitivity can be thought of kinda-sorta maybe as a "hidden food allergy" if you squint at it just right. It's still incorrect to call it a hidden food allergy, though -- there is no immunoglobulin response, and exposure to tiny amounts tends not to trigger a reaction the way it does with real allergies.
Finally, confusing the matter even further, there is a conflicting set of terminology in use for non-IgE reactions (reactions that aren't mediated by the immunoglobulin E antibody). Some sources call a non-IgE mediated reaction a "non-IgE mediated allergic reaction"; other sources don't classify such an immunological response as an allergy at all. Whether a given non-IgE mediated food sensitivity is called a food allergy or a non-allergic food hypersensitivity seems to be a matter of whoever is writing the study.
Hypotheses for the rise in food allergies
Food allergies are more prevalent today than they were a century ago. Some of this is due to greater awareness of food allergies, and to an increased sensitivity (if not specificity) of food allergy diagnosis -- but that's not enough to explain the whole picture. Something else has changed in the developed world that has caused food allergies to become more prevalent.
One hypothesis that has gained a lot of traction is the hygiene hypothesis. Basically, the notion is that modern society lives in much greater conditions of cleanliness than it did at the dawn of the 20th century, and thus we are exposed to fewer bacteria when we are very young. It is early exposure to bacteria, so says the hypothesis, which teaches the body not to treat every Tom-Dick-and-Harry protein it encounters as a foreign invader. And indeed, there are biochemical mechanisms that have been studied which tend to support this hypothesis.
Direct evidence for the hygiene hypothesis is hard to come by, however. All we can really say at this point is that it hasn't been ruled out.
Wider variety of food
Thanks to globalization, most people have access to far more cultivars of far more plants and meats than ever before. Some foods have also been genetically modified to increase production. A person living in a 19th century farming community might not even know what, say, a pistachio is, let alone have the opportunity to consume one. If this person was allergic to pistachios, they would never know. Furthermore, in a 19th century farming community that had regular access only to a few crops, if you did happen to be allergic to one or more of the staple crops, you weren't likely to survive to adulthood. While research is ongoing, the dead do not have allergic reactions.
Genetics and natural selection
There is evidence that many food allergies have a genetic component. However the genetics are complex, and not just a simple case of one gene per allergy. A general tendency to develop allergies appears to be heritable, as well as specific allergies. It might be supposed that in the past people with serious allergies would struggle to reach adulthood, and therefore natural selection would strongly reduce the frequency of genes predisposing people to allergies. But modern medicine means increasing numbers of people with allergies are reproducing and spreading their defective genes, and because of the complex relationship between genes and allergies, even allergies to novel foods will be more common.
Pirates and global warming
Purveyors of health woo never let little things like correlation does not imply causation get in the way of a good rant.
One such case is the notion that the increase in food allergies corresponds with the adoption of serum vaccines, as opposed to the earlier lancet-delivered vaccines. It also corresponds with the increase in global average temperatures, and the decrease in piracy on the high seas. It's one thing to point out, legitimately, that certain ingredients in vaccine serum have caused allergic reactions in the past. (Modern vaccine formulations tend to be a lot more hypoallergenic.) It's quite another to assume that this can spontaneously induce allergies to other substances that aren't even present in the serum. But then, anti-vaxxers tend to prefer appeals to emotion over balanced evidence.
The increase in food allergies also corresponds with the rise in genetically modified food crops. It should be noted, however, that all newly-introduced proteins in any GM crop have to be tested for their digestion time, and if any of them have long digestion times the food will not be deemed fit for human consumption. It is long-digestion-time proteins that carry the greatest potential to be allergens. Thus far, no cases of food allergies have been confirmed to be linked with any GM trait, though rumors abound. Incidentally, the University of Nebraska maintains a database of over 1700 known allergens., and none of them are proteins introduced via genetic engineering.
- The Straight Dope, "What purpose do allergies serve?"
- The Straight Dope, "Are peanut allergies for real?"
- Allergies: Dubious Diagnosis and Treatment, Quackwatch
- Schneider Chafen et al., Diagnosing and Managing Common Food Allergies: A Systematic Review, JAMA vol. 303 no. 18 (12-May-2010), pp. 1848-1856
- Consumer Reports: Food allergies are not rampant, and they can change over time, Washington Post, 23-Jan-2012
- Food Allergies: Facts, Myths, and Pseudoscience, on Science-Based Medicine
- Eggesbø et al., Prevalence of parentally perceived adverse reactions to food in young children, Pediatric Allergy and Immunology vol. 10 no. 2 (May 1999), pp. 122-132
- Stay Away From Cytotoxic Testing
- Statement on cytotoxic testing for food allergy (Bryan's test). Committee of Public Health, Bulletin of the New York Academy of Medicine', vol. 64 no. 1 (Jan-Feb 1988), pp. 117-119
- Such as this guy: http://www.drbralyallergyrelief.com/igg.html
- Science-Based Medicine article on IgG tests
- e.g. in this blog post here: Feeling lousy? Maybe you have food sensitivities
- Food Allergies: Suspect, Test, Avoid from WebMD
- "Allergy blood testing: A practical guide for clinicians" Cleveland Clinic Journal of Medicine
- An article covering just 1997-2008: Food Allergy Among U.S. Children: Trends in Prevalence and Hospitalizations
- "Genetics of Food allergy", Hong X, Tsai H-J, Wang X. Current opinion in pediatrics. 2009;21(6):770-776.
- Allergy – The Genetic Risk, Allergy UK, British Allergy Foundation
- Vaccines and the Peanut Allergy Epidemic, at a site called The Doctor Within.
- Peanut oil was introduced as a new vaccine excipient in the 1960s, but this excipient was never approved in the U.S.; later excipients used in the U.S. may have contained peanut oil, but even so, the peanut oil used in these adjuvants is supposed to be refined to remove any traces of peanut protein.
- There are over a thousand studies on genetically modified foods in biofortified.org's GENERA database. Thus far, none have shown a link between any GM foods and allergies