Beetle jelly is a source of sugar, moisture, and maybe trace amounts of minerals and vitamins if they were added to the jelly and if they haven't degraded completely. The majority of the protein found in the jellies would probably be the gelatin used.
I've noticed that long-lived, sap-feeding beetles are unable to maintain their mass on a diet of beetle jelly and I'm pretty sure that it's an insignificant source of anything but water and a little bit of sugar.