Well, there are 39 grams of carbohydrate in an average banana -- and about 162 calories. You have burned a lot of calories -- so weight-wise/loss you should be okay. However, it could impact your being in ketosis, and may have to do the "slide back into thing". For some people that would mean feeling hunger and headaches.
That was probably way too much exercise for someone on a VLCD.
But, if you HAVE to have something -- make it protein (it shouldn't affect your ketosis as easily).
MM