Hi Ange1a66
I had both investigations a couple
of years ago pre being diagnosed T2.
The usual advice they give for non diabetics is “white” food for a couple of days before, such as white bread, milk etc - all the bad stuff we diabetics should avoid.
Assuming you are doing LCHF, my best advice would be to stick to light dishes, such as homemade chicken soup, plain yoghurt etc.
When you can eat will depend on the timings of your appointment, just have lots of clear broth or simply water once you have taken the preparation meds.
To be honest, once you have taken the “cleaning” preparation you really won’t anything other than water ! Look on it as a couple of days of fasting.
Hope all goes well