Yesterday I covered Patrick’s response to criticism of his comments on the Gladys Block paper. Now, I’ll take a brief look at the reasons for Mr Holford’s continued support for York Test and York Test’s IgG blood testing kits.
Two types of antibodies, called IgE and IgG, are thought to be the main contenders for most allergic reactions. Both can be reliably tested using a technique known as ELISA.
Here’s my first problem with this response: IgE and IgG are said to be the ‘main contenders’ for allergic reactions. The expert view seems to be that the “significance of IgG anti-food antibodies is particularly uncertain since the sera of many children with such antibodies in their serum tolerate the foods in question perfectly well.” (The American Academy of Allergy, Asthma and Immunology, via breathspakids). The breathspakids blog is also the source for this quote from The Australasian Society of Clinical Immunology and Allergy:
IgG antibodies to food are commonly detectable in healthy adult patients and children, independent of the presence of absence of food-related symptoms. There is no credible evidence that measuring IgG antibodies is useful for diagnosing food allergy or intolerance, nor that IgG antibodies cause symptoms. The exception is that gliadin IgG antibodies are sometimes useful in monitoring adherence to a gluten-free diet patients with histologically confirmed coeliac disease. Otherwise, inappropriate use of food allergy testing (or misinterpretation of results) in patients with inhalant allergy, for example, may lead to inappropriate and unnecessary dietary restrictions, with particular nutritional implications in children.
Given that there is no credible evidence that measuring IgG antibodies is useful for diagnosing food allergy or intolerance, I can’t see how it can possibly be relevant that IgG “can be reliably tested using a technique known as ELISA.”
Patrick also provides a reference to back up his claims for effectiveness. This reference is to a survey on whether people felt better after following a diet which eliminated the foods that had been identified as allergens by Yorktest. I had a look on Pubmed to see whether I could find G Hardman, Journal of Nutrition and Food Science (2007), vol 37, pp 16-23. Nothing. Which is a shame really – I had quite fancied reading that. Apparently, the study found consistent evidence that noticeable benefit was gained from removing offending foods from the diet. We just don’t know what kind of evidence – were the respondents simply reporting on how they felt or were there objective measures of benefit? Holford then points out that: the more strictly they followed their allergy-free diet, the better their results. That’s an interesting point. Until recently, I had never heard of the confounding effect of compliance. There is a fascinating piece in the New York Times that deals with the Bias of Compliance.
If you want to learn more about expert opinion on IgG, or the House of Lords or Advertising Standards Authority views on this kind of testing, Holford Watch have a piece here that includes direct quotations from a House of Lords committee and from an ASA adjudication. The breathspakids blog has an entire category on IgG. The Bad Science post about the show is here and you can listen again here. I love Radio 4.