Things like high oxalate content that, without hydration, can put you at risk of kidney stones.
As a ~vegan I once contracted gout!
What that taught me (via internet knowledge shares, the doctors were completely stumped) was an excess of nutritional yeast.
The daily recommended amount was 3-4 tablespoons per day. I was easily eating 15.
Apparently nutritional yeast has a thing called purines, also found in red meat, and is a cause for gout.
Cut it down to normal consumption levels, and the problem went away.
https://multimedia.efsa.europa.eu/drvs/index.htm
Some of the entries in this public nutrition database have daily maximum values.
That information needs to be more readily available.