I've done a lot of checking around on-line, and my general impression is that using beetle jelly doesn't really provide any nutritional advantage over banana. In fact, it seems that banana might actually be more nutritious than most jelly formulations. I just wish it wasn't so messy! Maybe if I try to concentrate on only using banana that isn't yet too ripe, it won't be as bad. If I use totally ripe banana, it melts down in just 72 hours into a disgusting, sticky mess that breeds up phorid flies! More solid, less ripe banana holds up noticeably better.
In addition to banana, I also give my beetles brown sugar syrup, so in any case, they should definitely be getting enough calories / nutrients.
Although there are now many different formulations for various kinds of beetles, it seems that jellies were originally developed mainly for stags, which don't care much for fruit, and normally feed on tree sap.