Under a nutritionist's care, my friend did an elimination diet.
After a month, she has lost a lot of weight, and she no longer has her former all-over-body-pain which was almost disabling.
She found out that there are many foods that she shouldn't eat and now, if she does eat even a bite, she can feel the negative result.

I had the same experience. Two years ago I went to a natural alternatives lady who uses the Asyra method to see what is really going on in my body and it turned out that I have been allergic to dairy my entire life. I was always in and out of GI doctors offices without any relief whatsoever, just this drug and that procedure to lead me to just feeling like crap 24/7. After I eliminated dairy I felt like a million bucks and now I can’t even eat a little without vomiting. She also makes me go grain and gluten free for periods of time to give my intestines a chance to heal. GAME CHANGER. Our food supply is so toxic!