I can also test anything specific that you'd like to bring along , such as a face cream or an unusual food that you think may be causing your symptoms.
Not only does muscle testing pin point which foods/substances your body has an issue with, but also the severity of the problem. So if you think you may have an issue with cow's milk for example, the testing will reveal immediately whether you do or not. I would then go on to see exactly whether it's the lactose (sugar) in milk that is causing the issue or the Casein (protein).
The next test would be to see how severe the issue is, i.e a sensitivity (able to tolerate some) or an intolerance ( unable to cope with the tiniest amount).
The final test would be to see if the problem food is the one that's causing the symptoms you're experiencing.
So if a client present with a rash and proves to be sensitive to casein, I'd be testing to see if the casein is contributing towards the rash or not. If it does test positive, the rash should begin to heal within days of not drinking or eating anything containing casein. If it tests negative, then I go back to the other common problem foods to find the culprit.
Lastly I would be testing the various milk alternatives freely available to see which of them suits the client. If lactose is the issue (and frustratingly, it often isn't) then it's relatively easy just to choose lactose free dairy products. However, to my knowledge there aren't yet any casein free foods available to buy as of yet, so testing nut milks, rice milk, oat milk etc is a sensible approach , as most of my clients have an intolerance or sensitivity to some of these too. For example I saw a 6 month old baby who had been put on a soya based formula after suffering colic and diarrhoea on formula based on cow's milk. She then went on to suffer constipation on the soya, so finding which alternative suits can save a lot of time and suffering (she thrived on the goat's milk formula that tested out fine for her).
If you'd like a brief explanation of muscle testing, please click on the video link from The Association of Systematic Kinesiology.