Food intolerances, presenting as abdominal pain, nausea, bloating etc. are less well understood as compared to food allergies.

For food allergies, we do IgE tests, which are useful in diagnosing IgE mediated allergies, like blood tests and skin prick tests. Some ‘Nutritionalists’, are doing IgG tests for food intolerances. There is no evidence for this and the results confuse the parents.

The American Association of Allergies says _ _ _

In the context of food, IgG signifies memory through exposure to a food.  Because a normal immune system should make IgG antibodies to foreign proteins (to include foods), a positive IgG test to a food is a sign of a normal immune system, and suggests tolerance or “memory” of the food rather than food allergy.  Therefore, IgG testing is not recommended for evaluation of food allergies.’

If the patient has previously eaten the food (milks, eggs), he or she would likely have IgG to the food.

http://acaai.org/resources/connect/ask-allergist/can-igg-blood-testing-check-delayed-food-allergies

https://ramnikmathur.com/2017/08/08/tests-for-allergies/