The hypothesis was that IgG tests may pinpoint foods that in some way trigger ADHD symptoms. This was found to be incorrect.

"We recorded no difference in behavioural effects after challenge with high-IgG or low-IgG foods. These results suggest that use of IgG blood tests to identify which foods are triggering ADHD is not advisable. However, IgG blood tests might be useful in other diseases." [1]

To me, this says that any deviation from restricted diet caused a relapse in ADHD symtoms. A less technical explaination about IgG testing here: http://www.tldp.com/issue/174/IgG%20Food%20Allergy.html

[1] http://marrym.web-log.nl/files/adhd-and-elimination-diet-rct...