Weirdly, the symptoms I get from sugar consumption are incredibly painful abdominal cramps and lower-GI issues. And the last things I’ve eaten to trigger those were granny smith apples and bing cherries.

Regarding grains (including wheat), I gave those up when I was about 20, about the same time I quit sugar. All my symptoms went away when I quit both of those and honestly I’ve never tried enough wheat/grains since to see if it even bothers me. But then again, I don’t really feel like reintroducing wheat would enrich my life to speak of, so I haven’t ever really felt motivated to even test if grains give me symptoms. I just don’t eat it.