Ok, experiment is over for me.
I had my first day at work since starting and I nearly passed out at the table (I work as an OR nurse). When I have to eat and then go scrub up for an operation that takes 4-5 hours, I need protein and fat in my belly to tide me over. I'm sure the spud diet works but not for someone who has to go many hours between meals.
I may well come back to this when I have some days off, or I may look at doing it on weekends instead of weekdays. I certainly can't do it on work days, it just doesn't work with my schedule.