If I were writing your 'eating & drinking' info on the PIP form, I would have been phrasing it along the lines of:
"My [name of the medical condition] means that I am frequently unable to eat. This is because my depression has affected my appetite to the extent that I have little or no appetite.
On a bad day I can only [describe a typical bad day]. On a better day I am only able to [describe what happens].
I need [describe whatever help/support you need/get] in order to be able to eat at all. Without this help I would [describe what happens when you have no assistance/support etc].
My [medical condition] means that I find it very difficult to access food to eat. This is because my depression affects me to such an extent that I find it difficult to motivate myself to get out of bed. Furthermore, my anxiety means that I struggle to leave my bedroom in order to get to the kitchen to prepare food.
On a bad day I [describe your worst days].... On a better day I [describe the difficulties you still encounter]
I need [describe what you need in order to be able to make it out of bed and to the kitchen].
My [medical condition] means that I suffer pain when I try to get out of bed/reach the kitchen/prepare food. This is because [describe the problems] etc
Then repeat with the description of bad days and better days.
The only blank boxes on DS2's form were the ones that definitely didn't apply to him, eg taking medication, and the one about being able to read.