I'm pretty sure the guidance is no, you should not be on a vlcd when you have surgery. Given that your body has to heal afterwards too, I think you're advised not to be on a vlcd for something like 3 months afterwards. Your body is effectively conserving energy, and not doing anything 'non-essential' - which is why for some people hair starts to fall out etc. After surgery, you need your body to be firing on all cylinders to kick in all the healing that will be needed.
Something like low carb, but where you're still having more calories may be better? I would talk to your doctor about it, or you could contact Exante customer help.