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No expert here, but I think fasting can sometimes trigger disordered eating in some people. Binge eating, etc. People are just so varied and so is nutrition.

I haven't seen anything for healthy individuals. There are some studies though that have found negative effects for pregnant women and unborn children.

See https://www.sciencedirect.com/science/article/pii/S016762961...

It also depends on what type of fasting you're talking about; Here's a video about "alternate day fasting" that shows it can mostly be good, unless you already have high cholesterol or are diabetic: https://www.youtube.com/watch?v=MKFWvYtm6Ck

(check out the recent videos on that channel as well - he's just done several videos covering scientific studies about all types of fasting!)

There are papers showing negative side effects (bulimia, eating disorders), but a point easily overlooked is that if you are not mentally prepared, it's a though ride.