We were tested by a lab in Texas (see http://www.enterolab.com/) and through a blood test our doctor authorized. Many people are tested by an upper gastrointestinal scope, to find out if the villi are flattened in the small intestine. Initially, we went off of all dairy products, along with gluten. This was extremely difficult, and gratefully after two years we were able to re-introduce dairy products. It took a while to start feeling better, but it is huge blessing in our lives to have better health now.