Sugar. Ok, that’s a slight exaggeration. I don’t eat anything with added sweeteners. (Like, if it has sugar, honey, HFCS, corn syrup solids, cane juice, apertame, sucralose, agave nector, dates, maple syrup, etc, that’s just a deal breaker for me.) And I don’t eat anything that has natural sugar any sweeter than a tomato, red bell pepper, or carrot.
I’ve been doing that for the last 15 years at least and made very very infrequent exceptions. (Like, I can literally count the times I remember making exceptions to this rule in the last 15 years on one hand.)
…because any time I do make an exception, I have severe gastrointestinal symptoms.