A limited diet where people continually eat the same things over and over will almost always lead to food sensitivities . Coupled with an unhealthy bowel and congested liver and you get out-and-out allergies.
I was sensitive to wheat in any form, gluten, corn, tomatoes, and still do poorly with nitrates . But since I cleaned up my diet and bowels etc., I find I can re-introduce foods and do fine. Tomato sauce still gets me though, I think I'm just the wrong body type for nightshade veggies.