I once did a water only fast for 6 days then tested foods one at a time. I
found that chocolate made my knee get really sore, soreness that I usually
attributed to an old injury. Beef made me hungry. Non-organic potatoes made
me have symptoms of influenza. I had been having upper respiratory
"flu" for years until I gave up potatoes. I was off all potatoes for 10
years only to discover that I could eat organic potatoes. I think it was the
chemical that they spray them with to prevent eyes of the potato from
growing on the grocery store shelf that was causing my "flu" symptoms.

I think that even paleo foods, like beef, that are adulterated with various
chemicals or hormones can cause problems.

Any food or additive chemical can cause any problem.

Michael