Study helps explain how xanthan gum is processed in the gut
labblog.uofmhealth.org
labblog.uofmhealth.org
The most basic side-effect is that your gut craves what you eat. So if you stop eating it you'll exhibit addiction-like symptoms of really wanting to eat it again. For this reason to get a clear picture you should perform dietary experiments over a long enough period, like a month.
I've done many of these, including eating nothing but banana for a month. Highly enlightening.
I would expect it to be bad, but the fact that you didn't go into details has me curious.
Following the experiment I've adopted to filling nondescript feelings of "eat something" with banana. It's decently nutritious filler and convenient snack, but doesn't make for a meal foundation.