the way that you can tell if they have an intollerance is to take them off all of the food you think is causing the problem for a week. During that time, everytime they are eating, you take their resting pulse so you have a really good idea what is normal for them after the week.
Then you give them a small amount of the offending food, and you start taking their pulse whilst they are eating it at 10 seconds, 30 seconds, 1 minute, 2 mins, 5 mins, 10 mins 15 mins.
You are looking to see if the pulse raises at all. If it does then there is a intolerance- but if it doesn't then there isn't.

Its sounds hard to try and keep a little one quiet, but it is effective and less envasive than intolerance tests.

HTH and good luck