I'm celiac and my symptoms* can best be described as hyper sensitivity to addictive foods. I suspect this is more common than has been studied [1] as my main symptom was daily sinus headaches.
The first thing I cut out was gluten. Gluten has been shown to act like an opiate in people with autism. [2] I believe I was going through a short time-scale withdrawal when consuming it regularly. That was the best I ever felt, but I would still get the occasional sinus headache. Having tasted the good life, I was on a mission to feel 100%.
The next thing I cut out was caffeine. It was tough. On all my attempts to give things up, I've gone back and forth multiple times. I joke that it's to "confirm" the trigger, but really it's because giving up tasty foods is tough. Each time I go through an initial withdrawal. Bad sinus headache, shaking (nerves), vomiting, stomach problems. It took about a month until my energy levels were back to normal after giving up caffeine. I would usually come home and work on side projects, I just didn't have the energy for a solid month. If it didn't get better I was ready to suffer through the headaches to get my energy back, but it did get better.
There is an amazing gluten free restaurant near me, and they have pizza. I was eating pepperoni pizza's pretty regularly (because omg pizza) and still getting headaches. Narrowing it down, only eating their pizza in the day and seeing what happened I was able to identify what it was that was triggering headaches on those days. I brought it up to the owner and he pointed out sodium nitrite as an ingredient in the pepperoni. This is a common ingredient in bacon and BBQ meats, which explained my sinus headaches with those too. Did a few tests and it seemed consistent. There is uncured bacon and pepperoni but it's just a trick. They use celery powder or celery juice to cure it. Celery contains sodium nitrite. This also explains the headaches I get with Old Bay seasoning (contains celery).
I feel there is a perfect phrase to describe this, but I can't think of it, so I'll just say I cut down more of the forest I could more easily identify the trees that were giving me sinus headaches. While I had given up caffeine, I was still a total sugar fiend. Caffeine-free root beer, bowls of vanilla ice cream doused in sprinkles. With my limited diet it was pretty easy to identify the causes. Sugar was really rough to give up. I don't know if it was the quantity I was eating, how long I had been eating it, but it was bad. With sodium nitrites I just get a sinus headache when exposed to them. With sugar I get the full symptoms described above. I went back and forth on sugar a few times but the withdrawal symptoms (after giving it up) are what made me finally say this is horrible and I'm never doing it again.
The final thing was MSG. I eat a lot of chips, since I can eat potato and corn. I was particularly fond of the Ruffles Cheddar and Sour Cream ones. But lo' a headache! Reading over the ingredients, monosodium glutamate. I didn't know that was MSG at first, I had to Google each ingredient, but when I found out, it made a lot of sense.
Giving this stuff up is difficult. I'm actually incredibly thankful for my hyper-sensitive symptoms as it has gotten me to start eating healthily. It has also made me realize how much addictive stuff is put into foods and how scarcely it is researched.
*Celiac symptoms vary wildly, and I can only speak from my own experience.
1. http://www.aaaai.org/ask-the-expert/coeliac-disease-sinusiti...
2. http://www.tandfonline.com/doi/abs/10.1517/14728222.6.2.175